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12.13: Amphibian Reproduction and Development - Biology


What changes must occur for these tadpoles to move onto land?

These are tadpoles of the Yellow-Bellied Toad. Of course these tadpoles are born in the water. You can see the beginning of the formation of the hind limbs.

Amphibian Reproduction and Development

Amphibians reproduce sexually with either external or internal fertilization. They attract mates in a variety of ways. For example, the loud croaking of frogs is their mating call. Each frog species has its own distinctive call that other members of the species recognize as their own. Most salamanders use their sense of smell to find a mate. The males produce a chemical odor that attracts females of the species.

Amphibian Eggs

Unlike other tetrapod vertebrates (reptiles, birds, and mammals), amphibians do not produce amniotic eggs. Therefore, they must lay their eggs in water so they won’t dry out. Their eggs are usually covered in a jelly-like substance, like the frog eggs shown in Figure below. The “jelly” helps keep the eggs moist and offers some protection from predators.

Frog Eggs. Frog eggs are surrounded by “jelly.” What is its function?

Amphibians generally lay large number of eggs. Often, many adults lay eggs in the same place at the same time. This helps to ensure that eggs will be fertilized and at least some of the embryos will survive. Once eggs have been laid, most amphibians are done with their parenting.

Amphibian Larvae

The majority of amphibian species go through a larval stage that is very different from the adult form, as you can see from the frog in Figure below. The early larval, or tadpole, stage resembles a fish. It lacks legs and has a long tail, which it uses to swim. The tadpole also has gills to absorb oxygen from water. As the larva undergoes metamorphosis, it grows legs, loses its tail, and develops lungs. These changes prepare it for life on land as an adult frog.

Frog Development: From Tadpole to Adult. A frog larva (tadpole) goes through many changes by adulthood. Notice the visible changes that occur at each stage. How do these changes prepare it for life as an adult frog?

Summary

  • Amphibians reproduce sexually with either external or internal fertilization.
  • Amphibians may attract mates with calls or scents.
  • Amphibians do not produce amniotic eggs, so they must reproduce in water.
  • Amphibian larvae go through metamorphosis to change into the adult form.

Review

  1. Describe the life cycle of frogs.
  2. Describe the parental involvement of most amphibians.
  3. Define metamorphosis.

Amphibians Evolution

Class Amphibia includes frogs. roads, salamanders and caecilians. Class name shows that amphibians move between water and land. They spend one stage or their life in water and another on land. Amphibians are tetrapods. Term tetrapod is a non-taxonomic It is used for vertebrates other than fishes. Most tetrapods are adapted on land.

PHYLOGENETIC RELATIONSHIPS

Evolution of land vertebrates: Many adaptive radiations produced in vertebrates during first 250 million years of vertebrate history. Thus the vertebrates filled most aquatic habitats Prehistoric waters contained many active, powerful predators however vertebrates sere absent on land. Only some arthropods lived there as predators. Therefore, there was no vertebrate predator on land to capture animals that moved near the edge. Some vertebrates developed lungs for breathing and muscular fins for moving. These animals found ample food on land in the form of arthropods. The arthropods are the major component of the diet of most modern amphibians. Thus evolution of amphibians took place. Then adaptive radiations were produced in amphibians. It produced greater variety of amphibians than exists today. Later convergent and parallel evolution took place in amphibians. Then widespread extinction took place.

First amphibian: No one knows what the first amphibian was. The structure of limbs, skulls and teeth of lchthyostega are similar to the earliest amphibians. Two lineages of amphibians are formed in the late Devonian and early Carboniferous periods. These lineage can be differentiated by the structure of roof and the attachment of posterior portion of the skull to each other.

1. Amniotic lineage: One lineage of amphibians became extinct in the late Carboniferous period. An amniotic egg evolved in this group. It resisted dryness. This lineage is called the amniotic lineage. This lineage formed reptiles, birds and mammals.

2. Nonamniote lineage: A second lineage flourished in the Jurassic period. Most of animals of lineage have become extinct. But some of them gave rise to the three orders of living amphibians. This lineage is called the nonamniote lineage.


The Herpetological Society of Ireland

Credit: Trish Hartmann

The typical life cycle of an amphibian is often exemplified by that employed by Ireland’s native Common Frog (Rana temporaria). A large number of eggs are laid in a lentic water body and externally fertilized. The young undergo an aquatic larval stage before emerging on land as froglets. Once the eggs have been laid, the parents afford no further care to the young (McDiarmid, 1978).

This, somewhat hands-off approach to parenthood is, however, but one of the many reproductive strategies employed by amphibians, and in particular frogs: for some species go to extraordinary lengths to ensure their offspring get the best possible start to life.

To better understand the significance of these reproductive strategies and why they make such interesting subject matter, it may help to discuss these strategies in the context of the r/K selection theory.

r/k Selection:
The concept of r and K selection was first presented by ecologists MacArthur and Wilson (Pianka, 1970). The basic premise is that animals adopt one of two techniques for reproduction. Animals that are r-selected have a large number of small young in which they invest no parental care following birth. K-selected animals have a small number of relatively large young in which they invest a huge amount of energy. In reality, the r/K division is more of a continuum than two separate strategies.

Which technique is used is often a reflection of the stability of the environment in which the animal lives. According to r/K selection, unstable conditions should favour r-selected species because they have the ability to produce large numbers of young quickly, allowing the population to rapidly recover from a crash. Invertebrate pests are a commonly cited example of r-selected species. Insecticides can kill the vast majority of a population of pests, but the remaining individuals can restore the population to its former strength in a relatively short period of time.

K-selected species thrive in stable conditions and produce small numbers of highly developed young. These young have much higher survival rates due to parental investment, but these species have a poor ability to recover from population crashes. Whales are an example of a K selected species. While the young receive a great deal of maternal investment and are often too large to be considered prey, it may take decades to restore the population to its former levels if the population suffers a crash (from excessive whaling for example).

The difference in clutch/offspring size is essentially a consequence of metabolic budgeting. The animals devote a fixed amount of energy to reproduction, so if they invest less energy in zygote production then they can afford to offer further energetic investment afterwards.

While the “typical” amphibian reproduction strategy would fall under the r end of the continuum, those that fall closer to the K end are some of the most remarkable and unbelievable adaptations that the animal kingdom has ever produced.

Spotted salamander larva Credit: Brian Gratwicke

Urodella:
Parental investment among the urodella is not particularly common, but there are some very interesting exceptions.
The Alpine salamander (Salamandra atra) retains the eggs in its oviduct for between 2 and 5 years (Blackburn, 1999). They give birth to 2 fully developed young (one from each oviduct). For the first year of gestation the young feed on unfertilized ova and ova that were fertilized later than the first ovum. After the first year, this resource is exhausted. At this point, a small section of the mother’s oviductal epithelium, the zona trophica, becomes highly secretory. The young feed on these secretions for the duration of their gestation (Pough, 2007, Wake, 1993).

A more common form of parental investment in salamanders is egg attendance. Female Mountain Dusky Salamanders (Desmognathus ochrophaeus) stay with the eggs until such time as they hatch. The level of aggression utilized in defence of the eggs increases as time progresses. This is in essence an insurance policy. Should she lose the clutch early on, she may still be able to produce another clutch that season. If she loses the clutch late on, she will have suffered too great a loss in condition to produce a new clutch (Forester, 1983).

Silverstoneia flotator male carrying tadpoles. Credit: Brian Gratwicke

Caecilians:
Caecilians are perhaps the least well documented amphibian group, which is unfortunate because they display some very unique behaviours, particularly when it comes to reproduction.

The caecilian Boulengerula taitana lays eggs that develop directly to miniature adults. Both mother and offspring possess unusual adaptations. The mother produces a lipid rich monolayer of skin periodically. The young have specialised dentition that they use to feed on this nutritious layer of skin. As the offspring develop, their dentition changes to suit their adult lifestyle (Kupfer et al., 2006, Muller et al., 2009).

Geotrypetes seraphini Credit: Wagon16

Caecilians of the genus Typhlonectes retain larval young in the oviduct. The young have a pair of large sac like gills which function as a pseudo-placenta, absorbing nutrients from the mother (Wake, 1993).

The Mexican Caecilian (Dermophis mexicanus) also retains the young in its oviduct. Once the egg yolk has been exhausted, the young feed on a nutritious secretion of the oviductal epithelium. The young have special foetal dentition that they use to scrape the oviductal lining. After the birth the young shed their foetal dentition and acquire their adult dentition quickly (Muller et al., 2009).

Leptodactylus savagei tadpoles in a foam nest. Credit: Rob Gandola

Anurans:
The greatest diversity of reproductive strategies can be seen in the frogs and toads.

The Western Nimba Toad (Nimbaphrynoides occidentalis) is a viviparous species that feeds the young on oviductal secretions for the final 2 months of gestation. The gestation lasts 9 months. For the first seven, the female resides in an underground nest to escape the dry season (Wake, 1993).

The Creole Frog (Leptodactylus ocetlatus) lays a foam nest which floats on the surface of the water body. In this way the young are protected from aquatic predators for the early stages of their development. Once the eggs hatch, the young form a school that moves around the pond feeding. The mother follows the school around and attacks potential predators attempting to feed on the larvae (McDiarmid, 1978).

The Surinam Toad (Pipa pipa) has quite a unique method of brooding its young. During amplexus the female turns herself upside down so that the eggs are rolled up on to her back with some assistance from the male. The females back will become swollen and puffy. The eggs sink into the modified skin and become almost completely enveloped by it. The young undergo metamorphosis in these pockets and emerge 3-5 months later as fully developed froglets (Rabb & Snedigar, 1960, Rabb & Raab, 1960, 1963).

Engystomops pustulosus mating. Credit: Rob Gandola

Those frogs having pouches (Amphignathodon, Flectonus, and Gastrotheca) are termed marsupial frogs (Duellman & Maness, 1980). Of these, some retain the young until metamorphosis is complete, while others retain them until an advanced stage of metamorphosis. All of these frogs brood their young in dermal pouches. The shape, position and capacity of the pouches vary between species. The sex of the brooding parent also varies between species. In Flectonotus pygmaeus, eggs are laid one at a time at one minute intervals. As the male fertilizes each egg he assists in its insertion into the pouch. When the eggs hatch, the female moves to a small water body, such as a bromeliad, allowing the advanced tadpoles to swim out of the pouch. The young then complete metamorphosis in approximately two weeks (Elinson et al., 1990).

The now extinct Gastric Brooding Frog (Rheobatrachus silus) as its name suggests, maintained their young in the female’s stomach. Once the eggs had been fertilised she would swallow them. The eggs would secrete Prostoglandin E2, which caused gastro-intestinal stasis and prevented the mother from producing gastric acid (De La Lande et al., 1984). During the brooding period, the stomach becomes highly distended and expanded to the point of inhibiting normal function of the mother’s lungs. Eight weeks later, the young were regurgitated as fully developed froglets. Eight days after the birth, the gastrointestinal tract of the mother returned to normal functionality (Gibbins & Tyler, 1983, Wake, 1993).

Darwin’s Frog (Rhinoderma darwinii) maintains their young in the vocal sac of the father. For the first 20 days after fertilisation development of the eggs occurs in moist ground. At this stage, they begin to exhibit muscular activity and it is this cue that prompts the male to pick them up one by one and guide them into his vocal sac. The average clutch size is 11. The young develop fully inside the father’s vocal sac and emerge about 52 days later (Busse, 1970). There is some evidence to suggest that the father may supply the young with nutrition during the brooding period (Goicoechea et al., 1986).

Some species exhibit direct development of the eggs. Large eggs allow the young to forego the vulnerable aquatic

Isthmoyla lancasteri breeding. Credit: Rob Gandola

larval stage. The Jamaican Frog (Eleutherodactylus cundalli) goes one step further. They deposit their eggs deep inside caves where they are less vulnerable to predation and the environment is stable. The female attends the clutch until they hatch. The froglets then climb on her back and she transports them outside the cave where food is more plentiful (Diesel et al., 1995).

When it comes to parental care, it is the Dart frogs that are the most renowned. Frogs of the genus Dendrobates exhibit complex parental care. In species such as Dendrobates auratas, Dendrobates tinctorius azureus and Dendrobates tinctorious a small clutch is laid in leaf litter. The male then attends the clutch until they hatch, at which point he transports them to phytotelma (water bodies held by plants such as pitcher plants) where they complete their development (Summers et al., 1999).

A similar strategy is utilized by frogs in the genus Oophaga. The Strawberry Dart-Frog (Oophaga pumilio) is perhaps the best known. In this species, the male attends the clutch until they hatch, but it is the female that transports the young to phytotelma (Limerick, 1980). She returns to the pools periodically and deposits unfertilized ova for the young to feed on (Brust, 1993, Summers et al., 1999).

Analysis:
While the assemblage of reproductive strategies utilized is diverse, they seldom deviate far from basic ideals. To understand why a particular strategy may work for a species one must weigh up its benefits against its costs.

Hyalinobatrachium fleischmanni attending a clutch. Credit: Rob Gandola

Egg attendance:
So what advantages does clutch attendance offer? It reduces predation during early life stages as parents can defend the clutch by attacking would-be predators. One particularly interesting case of attendance is that of Centroienella valerioi, a species of Glass Frog. The male has a reticulated appearance that makes him look very similar to his clutch. In this way, if egg-feeding predators mistake the male for the clutch and are attacked, they may be dissuaded from attacking the clutch in future. This form of camouflage also serves to protect the male from predators who are uninterested in amphibian eggs (McDiarmid, 1978).

Another major advantage of egg attendance is the ability to monitor the eggs condition and prevent developmental problems. Parents can help prevent desiccation of the eggs and can remove eggs that show signs of fungal infection. Large eggs are more susceptible to developmental anomalies, which the parents can counteract through frequent manipulation of the eggs (McDiarmid, 1978).

This strategy is not without its costs. Egg attendance reduces the parent’s ability to feed and mate, though in many species the male will continue to call for mates and may attend clutches from multiple partners (Beck, 1998, Burrowes, 2000).

Phytotelm Breeding:
This strategy is particularly helpful for species who continue to care for their young during the aquatic larval stage because the small enclosed bodies of water make the young easy to locate. By leaving the young in a small pool, such as those formed by a bromeliad axil, the parents ensure the young are safe from aquatic predators. The downside is that food is limited, so species that exhibit phytotelm breeding are often capable of completing metamorphosis without feeding or are provisioned with food from their mother in the form of infertile ova (Alves-Silva & da Silva, 2009, Brust, 1993).

Viviparity/Internal brooding:
Viviparity is commonly utilized by species in colder environments. By retaining the young until they’re fully developed, the mother protects them from extreme weather, and helps ensure that the temperature of the eggs is sufficient for development. The downside is that a lengthy gestation will prevent females from mating again and large developing young may impede the female’s efforts to feed and move. In species where the young feed on oviductal secretions, there is also the added energetic cost of nourishing the young.

Internal brooding in modified structures (stomach, vocal sac etc.) and dermal brooding provide the young with a moist, stable environment in which to develop. The young also gain extra protection from predation, because they are only ever as vulnerable as the brooding parent. There is a cost to the parent. As with viviparity, the young may impede the parent’s movement, and may even interfere with proper organ function (Gibbins & Tyler, 1983).

While parental care would appear to be more complex than the “traditional” amphibian life cycle, the complexity does not necessarily imply that parental care is a better strategy. The traditional strategy has its own pros and cons. The parents expend all their reproductive energy in a short time, allowing them more time to recover for the next season. The young have the benefit of numbers to reduce each individual’s risk from predation. Larger clutches will have a higher diversity of mutations, some of which may prove beneficial. The cons are quite obvious. The eggs are susceptible to predation and the young can do little to avoid it, the aquatic larvae are also highly vulnerable to predation. If fungal infections develop on the eggs, there are no parents present to reduce its spread etc.

These tadpoles were found in a pool formed in a tree hollow. Credit: Rob Gandola

Regardless of the strategy employed, amphibians are always at the mercy of their aquatic origins. The young must be kept moist at all costs. By evolving complex parental strategies that allow them to brood young successfully in terrestrial environments, amphibians can exploit a more diverse range of niches and reduce their dependence on fixed water bodies.

About the Author: Rob is a zoologist specialising in invasive freshwater bivalves. He is the PR Officer for The Herpetological Society of Ireland. Find him on Twitter here.

This article was originally produced for the HSI’s publication Lacerta. Reproduced here with minor additions.


Amphibians: Structure, Respiration and Sense Organs

In this article we will discuss about Amphibians:- 1. Origin of Amphibia 2. Factors that Caused Amphibian Evolution 3. Probable Ancestry 4. Structure of Amphibians 5. Digestive System of Amphibians 6. Respiratory System and Sound Production 7. Circulatory System 8. Nervous System 9. Urinogenital System 10. Reproduction and Development 11. 11. Reasons for Extinction.

  1. Origin of Amphibia
  2. Factors that Caused Amphibian Evolution
  3. Probable Ancestry
  4. Structure of Amphibians
  5. Digestive System of Amphibians
  6. Respiratory System and Sound Production in Amphibians
  7. Circulatory System of Amphibians
  8. Nervous System of Amphibians
  9. Urinogenital System of Amphibians
  10. Reproduction and Development of Amphibians
  11. Reasons for Extinction of Amphibians

1. Origin of Amphibia:

During the middle of Devonian time, the bony fishes had differentiated into the actinopterygians on one hand and into the dipnoans and crossopterygians on the other. The climax of evolution was reached when the descendants of some crossopterygians left water and invaded land. This event of transi­tion from water to land ushered a new phase in vertebrate evolution, the beginning of the land vertebrates.

The amphibians started the beginning of tetrapod history. By invading a new environment on land, the amphibians opened broad avenues for further evolution over a wide range of structural and functional adaptations. Before going into the discussion on the ancestry of the amphibians, the steps the first amphibians have taken to meet the basic requirements for life on land are described below.

The problem of terrestrial locomotion with additional gravitational complications was solved by profound changes in all the parts of the tetrapod body.

(a) The amphibian head attained power­ful musculature with corresponding changes of the articular processes of the skull and its adjacent endoskeleton.

(b) The lower jaw apparatus developed elaborate musculature for its operation and support.

(c) The vertebral column loses flexibility and gained strength and rigidity by ossification.

(d) The pectoral and pelvic girdles sup­port the limbs and also protect the important visceral organs from injury which may result from new upward thrusts. Walking on land resulted upward pressure. This upward thrust caused the diminution of dermal skeleton of the girdles. Powerful scapula and triradiate pelvic girdle with elaborate ilium are some of the important modifications in the girdles. These modifications are supplemented by the development of endo-skeletal processes for firm attachment of associated muscles.

(e) The amphibians have developed two pairs of limbs. These are well-equipped with adequate muscles and strong girdles to lift the body away from the frictional contact of the ground. The carrying of the weight of body on the four limbs has caused great change in the vertebral column.

(f) The problems of breathing in air are solved by developing well-formed lungs for gaseous exchange in air. The moist skin in modern amphibians also acts as an accessory respiratory organ.

(g) All amphibians possess well-developed vascular system, a new scheme for the development of lungs, i.e., introduction of pul­monary circuit. This has caused tremendous change in the structure of the heart and the circulatory system as a whole.

(h) Development of a middle ear cavity with a bone to transmit the vibrations from tympanum to inner ear helps in the intensifi­cation of the sound waves of air.

(i) The skin becomes suited for terrestrial life to resist desiccation.

The modern teleosts have reached the peak of evolutionary success amongst the primary water-living vertebrates. They have undergone extensive adaptive radia­tion. The air-breathing fishes, the dipnoans and the crossopterygians exhibit a close relationship with the amphibians and it is an apparent bio­logical truth that a group of such lung-fishes gave rise to the new terrestrial population—the amphibians.

So the chance for dipnoans and crossopterygians to hold the significant position in amphibian ancestry needs consideration. How did the early amphibians meet the new requirements imposed upon them as a result of change from an aquatic to terrestrial life is to be solved first.

The early amphibians must have fulfilled the basic requirements for living on land by making the following modifications:

(a) Partial loss of armours although present in some earliest amphibia, e.g., Stegocephalians.

(c) Development of terrestrial appendages by transforming the paired fins into limbs.

(d) Loss of internal gills and acquisition of lungs.

Dipnoi—foreshadowed amphibian organisa­tion:

It was a general belief that the dipnoans stand in the direct line of tetrapod descend, because the dipnoans show many structural and functional resemblances with the amphib­ians. Although the pectoral and pelvic girdles in dipnoans cannot support the weight of the body on land, these girdles foreshadowed some amphibian features in several ways.

(a) The internal skeleton of the paired appendages is well-developed in dip­noans.

(b) Paired appendages articulate with the respective girdles by a single proximal bony piece, which can be compared with the humerus or femur.

(c) Outward extension of myomeric muscles into the paired fins is quite suggestive of the arrangement of muscu­lature of the paired appendages of Amphibia.

(d) Ability to breathe air by lungs (modified swim-bladder).

(e) Pectoral girdle of Necturus resembles closely that of dipnoans.

Although the dipnoans present some specializations towards a method of living out of water, the total evidences direct quite clearly to the fact that they are not on the direct line of emergence of amphibia from fishes. The dipnoans exhibit too many specialised features and such a specialised group cannot possibly hold the ancestry of another group of animals.

Striking similari­ties, especially in circulatory and respiratory systems, are possibly due to the physiological convergence for living in similar condition of life. The dipnoans, today, give an idea of the form that probably linked the fishes with the amphibians. The dipnoans are usually regarded as the collateral uncle of the amphibia but not the father of first tetrapod.

Recently considering the morphological and anatomical point of views, D. Rosen et al., (1981), and Duellman and Trueb (1986) opine that the nearest living relatives of recent amphibians are lung-fishes than the crossopterygians but this has been criticised by Jarvik (1980) and other scientists.

Crossopterygians — direct the channel of amphibian evolution:

To trace the direct line of amphibian origin from the fishes, the importance of the crossopterygians in holding the probable starting point needs consideration. The early crossopterygians, as exemplified by the Devonian genera, Osteolepis and Eusthenopteron furnish the strongest support. Because they possess many features which are cer­tainly amphibian or lead towards amphibia.

(a) Bony pattern of jaws and skull are comparable to that observed in early amphibians.

(b) Two large bones on the top of a skull can be homologized as the amphibian parietal bones.

The posterior skull table of Osteolepis and Eusthenopteron is more similar to that of early amphibians (e.g., Ichthyostega and Eryops) than that of dipnoans (Fig. 7.49).

(c) The jaws of Eusthenopteron possessed labyrinthodont teeth characterized by in-folding of a tooth wall around a central pulp cavity (Fig. 7.50).

(d) Pectoral girdle presents certain features which are prerequisites for amphibian fore- limbs.

(e) Skull of Eusthenopteron contains almost all the elements observed in the early amphibians.

(f) Pectoral fin of Eusthenop­teron can be compared to the forelimbs of amphibia. The single proximal piece of bone can be homologized with the humerus and the next two pieces can be compared to radius and ulna.

(f) Various wrist and ankle bones, the bony elements of hand and foot have evolved from the distal bony complex of the crosspterygian fins.

Thus, in many respects, the crossoptery­gians show close similarities with the amphi­bian and it is expected that these fishes are the direct progenitors of the early amphibians.

Cladistic analysis in favour of osteolepiforms as the ancestor of early tetrapods does not support fully.

At present, a late Devonian crossoptery­gians, Panderichthyidae (e.g., Elpistostege and Panderichthys) seem to be in the line of direct ancestor of amphibians. The members of Panderichthyidae were crocodile-like fishes with fins instead of limbs.

Their hands, bodies and the skull roof were flattened and they had elongated snout. Their eyes were on the top of head and they had no dorsal and anal fins. Those features suggest a closer link with the first tetrapods.

The frontal bones were present in both Panderichthys and tetrapods but were absent in Osteolepiforms. The ribs of Panderichthys project ventrally from the vertebral column whereas in osteolepiforms the ribs of the vertebral column project dorsally.

The most dramatic and widely accepted event to note in amphibian evolution is the transformation of the crossopterygian paddles into amphibian limbs. The sequences indica­ting how amphibian limbs arose from a fish fin is a controversial issue. It is probable that the lobed fins of crossopterygians specially seen in Eusthenopteron have become transformed into the tetrapod limbs.

As the fish came on the land, the paired appendages perhaps first carried only the weight of the body and the muscles of the appendages became capable of only forward and backward movements.

With the evolution of the tetrapods on land, the limbs become elongated and shifted under the body to raise the body further away from the ground. While on land the muscles became modified and arranged around the shoulder and hip joints for balanced movement on land.

For the attachment of the muscles the girdle became expanded into plates consisting of dif­ferent characteristic pieces. The shoulder girdle of an earliest amphibia, Eogyrius, inherited a shoulder girdle closely similar to the Osteolepis.

Fig. 7.51 gives an idea of the possible stages of transformation of the crossopterygian girdles and fins into the tetrapod girdles and limbs respectively. The actual and documentary tran­sitional limb is still unknown. But the most ancient footprint of Thin-opus throws much light on the process of transformation.

2. Factors that Caused Amphibian Evolution:

What were the factors that led Crossop­terygians to leave their primal aquatic home and to come on land? There are different views. A few of them are given below.

Barrell (1916) emphasised that the Devonian was a dry period whence many streams and ponds tended to dry up seasonal­ly. Certain crossopterygians were capable of movement from drying pools to places where water was available. The periodic escapes from drying pools possibly caused the deve­lopment of tetrapod limbs.

(ii) Desire for excessive water:

Romer (1958) rejected the view of droughtness in Devonian period. He sugges­ted that amphibians and early reptiles were inhabitants of water until the Pennsylvanian period. He also suggested that it was the desire for more water that caused the first excursion of crossopterygians from one place to other.

Berrill (1955) is inclined, to think that the enemies in water forced crossopterygians to leave for land. Other factors were the abundance of food in land, lure for atmospheric oxygen and recurrence of unfavorable environment.

It seems that the real cause is neither safety nor food nor the desire to breathe atmospheric air, but an adaptation which has been imposed repeatedly upon the crossopterygians by recurrence of hostile environment.

Most pro­bably, during late Devonian period, due to excessive periodic drought, crossopterygians were forced to search for new fresh-water streams and lakes, where they can live and thus escape the risk of survival. By this way they had to cross dry land to find suitable water. From such a start the amphibians evolved in the geological age and became adapted to the new terrestrial environment.

During the Devonian time, some of the crossopterygians came to land from aquatic home. This group who was successful to come to land from water was probably the rhizodonts being represented by Osteolepis and Eusthenopteron. It was a very significant step to come into a completely new environment.

On coming to land these advanced air-breathing fishes became trans­formed into primitive amphibians. Fig. 7.52 shows the evolution of amphibian vertebral structures from the crosspterygian fishes. The most primitive amphibians, known the Ichthyostegid whose components of vertebrae have the similarity to the crossopterygians.

Due to the similarity of the components of ver­tebrae, between Ichthyostega and crossoptery­gians, it is supposed that amphibians have evolved from crossopterygians and from this basic type a radiation of several types of verte­brae among other amphibians and also in other groups of vertebrates may have evolved.

Figure 7.53 shows the phylogenetic tree of the amphibians. Ichthyostega exhibited a transitional phase by possessing an admixture of piscine and amphibian characters. Ichthyo­stega, although retained many distinct piscine characters, has paved the path of amphibian evolution.

4. Structure of Amphibians:

The living amphibians exhibit diverse structural adaptation. The caecilians have a degenerated structural organisation and they furnish all the basic modifications for fossorial life. They are the most primitive forms amongst the living amphibians.

The modern urodeles include a large number of families and genera. Although built on a common fun­damental plan, each family is characterised by having peculiar anatomical structures.

The urodeles include many giant forms. The largest amphibia is the Megalobatrachus of Japan and China which may even reach a length of about 1.60 m. Most of the urodeles are aquatic. The terrestrial forms have limbs and are plantigrade.

Anatomically, the urode­les occupy an intermediate position between the caecilians and the anurans. The anurans constitute the highly specialised forms and show wide range of adaptive radiation. Hyla shows an adaptation for arboreal life and pos­sesses adhesive discs at the tip of the digits.

The plate-like adhesive discs are not suctorial in action, but have a moist, corrugated anti­skid surface which helps in adhesion to the tree. During climbing, a sticky secretion is expelled from the adhesive discs by the action of collagenous fibres which operate the glands.

The adjustment of the adhesive discs is facilitated by the development of inter­calary cartilage between the terminal and penultimate joints. Another tree-frog, Chiromantis, has opposable digits.

In most of the tree-frogs, the webs between the toes are absent or reduced, excepting in Rhacophorus of East Africa where the elongated digits are webbed. It has been recorded that Rhacophorus malabaricus can glide from a height of more than 9 m and Hyla venulosa can glide from a height of 42 m quite effec­tively. In Hyla venulosa, the digits are not webbed.

The skin of amphibians consists of epider­mis and dermis. The epidermis consists of sev­eral layers and is renewed by ecdysis. This process of renewal is controlled by the pitu­itary and thyroid glands. Localised thickening in epidermis is observed in the larvae, special­ly in the formation of the horny larval jaws and teeth. The warts of toad are also the instances of such thickenings.

The skin of modern amphibians is naked and remains moist due to the secretion of integumentary glands. The moist skin is necessary for respiration and also possibly for temperature regulation. There are two types of skin glands in amphibians. These are: mucous glands and poison glands. The mucus secreted by the mucous glands keeps the skin moist.

The poison glands are well- developed in toad and salamanders. The parotoid glands of toad are the best examples of the poison glands. Most of the warts on the dorsal surface of the toad open to the exterior by a minute opening which leads into poison gland.

The gland produces active toxins. The secretion is venomous and causes nausea, respiratory and cardiac dysfunctions. The tox­ins are isolated as the bufogin and bufotalin. The poison of Dendrobates acts on the ner­vous system. The secretion of the dorsal glands of a warty Newt (Triturus cristatus) is ven­omous. The poison glands are defensive organs.

The skin of the larval amphibians is ciliated. The colour of the skin of amphibia may vary from dull to brilliant. The urodela usually shows brilliant colouration which has a protective value. The green colouration of tree-frogs is a protective device, because it harmonizes with the surrounding green fliage.

The spotted salamander and some frogs exhibit warning colouration. In some tree- frogs, the brightness of the body colouration may vary with the change of intensity of light.

The colour change is caused by the physio­logical adjustment of the deep-seated melanophores, guanophores and overlying lipophores. The skin of Gymnophiona is thick and contains groups of granular dermal scales enclosed in sacs and large multicellular poison glands (Fig. 7.44).

Skeletal Structures:

The exoskeleton was present in fossil amphibians. But in modern forms it is restricted to majority of the caecilians and some anurans. In caecilians, clusters of small dermal scales lie in the skin in most of the cases (Fig. 7.44) In a few toads, bony plates remain embedded in the skin of the back and these are dermal in origin.

In Brachycephalus of Brazil, the dermal plates on the back become fused with the neural spines. Small and horny claws are present in the larval stage of an Asiatic urodele, Onychodactylus and in an African toad, Xenopus. In Xenopus, claws are present at the tips of first three digits of his hind limb. Claws have been recorded in some fossil amphibians too.

The claws present in these amphibians, although fore-shadowed the emergence of claws in higher classes of vertebrate, are not true claws. In Pelobates, the highly cornified areas on the feet can be com­pared with the epidermal scales.

The skull in the living amphibians varies greatly. There is a general tendency towards reduction in the thickness and number of dermal elements in the skull. The inter-pterygoid vacuities and the orbits are greatly enlarged. The rami of the lower jaw are short and the skull becomes much flattened. The skull of the anurans is highly specialised among the amphibians.

The inter-parietal foramen (present in fossil amphibians) is totally absent in modern amphibians. The skull of toads is devoid of teeth, but in Amphignathodon true teeth are present on the lower jaw. In frogs, teeth are present on the lower jaw. The skull of urode­les has certain peculiar features of its own. It is less specialised than that of anurans and differs in many important respects.

The chondrocranium is lower in organisation with many degenerative or paedomorphic features. The parietals and frontals are separate and in some forms both lacrimals and pre-frontals are persistent. The skull of urodeles differs from that of anurans by having a large prevomer.

In caecilians, the skull is peculiar. It has large investing bones and a small but complete orbit is present there. The skull is a rigid struc­ture. The compactness is correlated with the burrowing habit. The lower as well as the upper jaws bear teeth. Like that of urodeles, a tooth-bearing coronoid is present in the mandible.

The vertebral column in amphibia is large­ly bony and the vertebrae are articulated together. The flexibility of the vertebral col­umn is lost to give more strength. This modifi­cation is due to the lifting of the body on the limbs. In urodeles which spend much of the time in water, the vertebrae lack ossification and notochord persists to help in swimming.

The transition from aquatic to terrestrial life causes the shortening of the vertebral column. In anurans, the vertebral column is composed of nine vertebrae and an un-segmented urostyle behind. The vertebral column is com­posed of nine vertebrae and an un-segmented urostyle behind.

The vertebral column is differentiated into:

(a) The cervical region represented by the atlas,

(b) The thoracolumbar region with variable number of vertebrae,

(c) A sacral region containing a large vertebra and

(d) A caudal region comprised of the tail verte­brae. The urostyle represents the caudal region in anurans. The transverse processes and zygapophyses are well-developed for the attachment of muscles.

The number of verte­brae is variable. It may extend up to 250 in urodeles and caecilians. In anurans, the verte­brae are procoelous except the ninth vertebra of Rana which is peculiar. The anterior surface of centrum is convex while the posterior sur­face bears a double convexity. But in urodeles, two types of vertebrae are encountered.

The primitive urodele as exemplified by Ambystoma has amphicoelous vertebrae and the higher urodeles possess opisthocoelous vertebrae. Some primitive frogs exemplified by Ascaphus and Liopelma possess free ribs. The skeletal features of the girdles and limbs have changed considerably in amphibians but the basic plan of the limbs and girdles remains same throughout the group.

In caecilians, these are secondarily lost due to fossorial adaptation. In fishes, the girdles and paired fins are small and are largely carti­laginous, but in amphibians the girdles have become greatly enlarged and modified due to their weight-bearing function. The appendicular skeleton in urodeles is greatly simplified, but in anurans these are highly developed and are quite suitable for terrestrial mode of life.

5. Digestive System of Amphibians:

Adult amphibians feed mostly on the arthropods, but the larval forms are usually omnivorous. They may be cannibals. As a result of similar food habits, the digestive sys­tem shows little variation. In most amphibia excepting toads, the teeth are present. The teeth are borne on the premaxillae, maxillae and vomer.

The teeth are very small and poin­ted and are used only to catch the prey. Biting teeth are present in adult Ceratophrys ornata. Amphignathodon, a South American tree-frog, possesses teeth on the lower as well as on the upper jaws. The salivary glands are absent but some oral glands are present which produce mucus.

In terrestrial amphibians, cilia are pre­sent in the oral cavity which keep the oral fluid in movement. In case of many urodeles, tongue is immovably fixed. It may be movable as seen in most anurans but it is free behind and fixed anteriorly.

The tongue is used to cap­ture the prey. The adhesive power of the tongue is enhanced, particularly in the frogs, by the secretion from the lingual and inters- nasal glands. The tongue is altogether absent in Xenopus and Pipa.

The oesophagus is a simple tube and is not sharply distinguishable from the stomach. The stomach is simple with folded mucous layer. Simple tubular gastric glands open in the folds. These glands are composed only of one type of cells. The glands produce pepsin and hydrochloric acid.

The intestine is short in adult amphibians and is marked off from the stomach by having a well-developed pyloric sphincter. But the intestine in omnivorous lar­val forms is much coiled like the spring of a clock. Caecum is absent in amphibian alimen­tary canal. But in some anurans, especially in Hyla arborea the large intestine has a conspi­cuous anterior caecum.

The liver and the pancreas have typical histological picture and produce bile and pan­creatic juices respectively. The liver is basically a single massive gland with right and left lobes. The gall-bladder lies just right of the midline of the notch between the lobes.

The liver is attached to the duodenum and stomach by gastro-hepatic ligament. The pancreas is a thin and elongated structure along the duodenum on the side away from stomach. The amphibians can live for a considerable period of time without taking any food. Proteus, Typhlomolge are the typical examples of cave-swelling animals (troglodytes). Axolotl larva may remain alive for about 650 days in starvation.

6. Respiratory System and Sound Production in Amphibians:

Adult amphibians are lung-breathers. The skin acts as an accessory respiratory organ both in water and on land. The skin is highly vascular and specially so in the buccopharyn­geal cavity. The larval amphibians respire in water by the gills. Such gills are retained in many adult urodeles. Few urodeles retain external gills as the respiratory organs in adults.

Both external and internal gills are pre­sent in anuran larvae. Ascaphus, living in the mountain stream of U.S.A., has reduced lungs which help the animal to live in water. In per-ennibranchiate urodeles, the lungs are simple saccular organs and the hydrostatic function is predominant. In Salamandra atra and Desmognathus, the lungs are absent.

In Astylosternus, an African frog, the lungs are vestigial. In caecilians, the tracheal lung may be present but the left one is always rudi­mentary. In aquatic urodeles, the lungs act secondarily as hydrostatic organ. In all these above cases, respiration is exclusively pharyn­geal and/or cutaneous.

In almost all amphi­bians cutaneous respiration is a remarkable supplementary respiratory adaptation. In Cryptobranchus, there are vascular folds in the epidermis into which blood capillaries pene­trate. The amphibians are virtually the pioneers where true voice is produced by the vocal organ.

The production of sound is a protective response for fear and the males call the females during breeding season. The noise is produced by the vibration of the vocal cords in the laryn­gotracheal chamber. The vocal sacs in the males of some anurans, developed as the buc­cal outgrowths, serve as resonator.

7. Circulatory System of Amphibians:

The heart of amphibia consists of a sinus venosus, two auricles, an undivided ventricle and a conus arteriosus. The conus arteriosus is made up of two regions: pylangium and synangium. The portion of the conus next to ventricle is called pylangium while the distal part is designated as synangium. The pylangium is more muscular than synangium.

The distal end of truncus arteriosus becomes expanded as bulbus arteriosus in some urodeles. The left auricle is absent in the plethodontid urodeles where the lungs and the pulmonary veins are missing. The auricles are completely separated by a complete inter-auricular septum. It is per­forated in Salamandra or may be fenestrated with intervening spaces in lung less urodeles.

The venous blood returns to the right auricle while the left auricle receives oxygenated blood. The spiral valve is present in anuran heart but it may be reduced in most urodeles or may be absent as in Necturus, Cryptobranchus and the caecilians. In all the amphibians where the conus arteriosus is present there are two sets of valves which prevent the back flow of blood.

The trabeculae carni (strands of muscle making up the muscular walls of heart) are observed in amphibians. These trabeculae are best deve­loped in the walls of auricles. In the urodeles where gills are retained in adults, the pattern of circulatory system is essentially fish-like. The venous system of the urodeles represents a tran­sitional stage between the fish and the anurans.

The RBC in amphibia are nucleated and oval. One of the notable features to record is the presence of largest RBC amongst the verte­brates. The RBC of Proteus measures about 58 pm in diameter. There are three types of leucocytes in amphibians.

These are lymphocytes, monocytes and polymorphs. The red blood cells are produced mainly in kidneys and are destroyed in the liver and spleen. The bone- marrow also serves as an important centre for formation of red blood cells in adults particu­larly in males during breeding season. The spleen is a source of lymphocytes.

8. Nervous System of Amphibians:

The brain of amphibia is basically built on the same fundamental plan in all forms. The prosencephalon is represented by two large evaginated cerebral hemispheres. The pineal organ is a simple sac in most cases, but in a few amphibians this forms a retina-like struc­ture. The optic lobes are well-developed. As the amphibians are sluggish animals, the cere­bellum is simple.

Sense Organs in Amphibians:

The sense organs are well-developed. Many aquatic adult amphibians and the larvae possess simple lateral line organs in the form of clusters of cells in an open pit. The skin contains tactile sense organs and chemoreceptors.

The olfactory organ Works both in water and on land. Organ of Jacobson is present in most amphibians. It is a special sensory sac developed as a diverticulum from the olfacto­ry chamber. It serves to test the scent of the food taken inside the mouth. It is absent in Proteus and Necturus.

The eyes of amphibia exhibit certain modifications due to transition from water to land. In water, the eyes were adapted for short­sighted vision but on land long-sighted vision becomes necessary. The eyes are extremely degenerated in caecilians and also in cave- dwelling urodeles. The eye ball is more or less spherical with a rounded cornea.

The lens is flattened in terrestrial amphibians, but in aquatic forms it is rounded. The eyelids are usually present in terrestrial forms excepting some primitive members. In tree-frogs, the eyelids may be transparent. The lacrimal glands are present in all the terrestrial amphi­bians. In aquatic amphibians, the lacrimal glands are absent but the lacrimal ducts are still retained in many cases.

In some caeci­lians, a single lacrimal gland occupies a posi­tion in the sightless eye-socket to lubricate the sensory tentacle. In all amphibians, the skin is also sensitive to light. This is highly developed in cave-dwelling urodeles.

The membranous labyrinth is com­posed of an utriculus with three semicircular canals, a sacculus with an outgrowth, called lagena. The middle ear consists of a funnel like cavity which communicates with the pharyngeal cavity by Eustachian tube. In this cavity, a rod (columella) is present which transmits the sound waves to the internal ear.

The columella fits into the fenestra ovalis by a broad foot (otostapes). The fenestra ovalis is partly occupied by a plate (operculum). So the transmitting rod is divided into an inner part, named as otostapes and operculum, a medium part called mediostapes and an outer part, designated as extra-columella.

In urodeles, caecilians and some anurans, the tympanic cavity and extra-columella may be absent. Cryptobranchus lacks the operculum. This is also absent in Xenopus and Pipa. In a terres­trial anuran, Bombinator, the tympanum and columella are greatly reduced.

9. Urinogenital System of Amphibians:

The kidneys in amphibia are of opisthonephric type and retain the characte­ristics of fishes. The shape of the kidneys cor­responds to the shape of the body. In urodeles and in a primitive frog, Ascaphus the kidneys are elongated.

Each kidney is divided into an anterior narrow non-renal part and a broad posterior renal part. In caecilians, the kidneys are extremely elongated and occupy the whole length of the body cavity. In case of anurans, the kidneys become condensed and divided into lobes. In amphibians, the genital organs develop from the genital ridges. Each such ridge is situated on the ventromedian aspect of the developing mesonephros.

The genital ridge is divided into three sectors:

(a) Anterior part (progonalis),

(b) Middle part (gonalis) and

The gonads proper develop from the gonalis. In anurans, the fat bodies develop from the progonalis while in the urodeles and caecilians, the fat bodies develop from the entire genital ridge. The testes in different amphibia assume various shapes.

The testes are smoothly rounded mass in anurans but in urodeles these may be elon­gated and lobed structures. In Desmognathus, each elongated testis is separated into a series of testicules which are budded off towards the anterior end, one for every year.

In caecilians, each testis is an elongated body and looks like a string of beads. The internal construction of testes is simple and consists of short seminiferous tubules. Each seminiferous tubule has a wide lumen and ends blindly.

The efferent ducts vary in number and extend up to the marginal canal of the kidney. Each marginal canal is developed from outgrowth of the cap­sule of primary mesonephric tubule of anterior portion of mesonephric kidney.

The meso­nephric tubules usually extend to epididymal duct. The kidney tubules serving as the carriers of sperms may retain their glomeruli in caeci­lians and a Salamander, Spelerpes, but in most amphibians the glomeruli are lost.

The testes discharge through the kidneys by the vasa efferentia. So the Wolffian or mesonephric duct serves as a urinogenital duct in males and as a ureter in females. In toads, a special Bidder’s organ is present. This organ is better developed in males.

The function of this organ is not known. It is assumed to be an endocrine organ, because it undergoes a cycle of size change. This organ is capable of developing into an ovary after castration in either sex. The Bidder’s organs develop from the gonalis sector just anterior to the gonad proper.

In females, the ovary is an irregular mass. The eggs are discharged into the body cavity. The Mullerian duct becomes swollen and con­voluted to become the gonoduct. It extends through the entire length of the body cavity. The eggs, after being discharged into the body cavi­ty, enter the ostium (opening of gonoduct) and traverse the duct.

In oviparous forms, the eggs get their jelly coating within the tube. In viviparous forms (Salamandra, Spelerpes fuscus, Typlonectes compressicauda, Dermophis thomensis), the eggs develop in the tube. The tube is divided into different parts in different amphibians.

(b) Infundibulum (wide lumen, thin wall and no glands),

(c) Tube (beset with glands in oviparous forms or without glands but mucous cells in viviparous forms),

(d) Uterus (wide lumen and much folded epithelium and

(e) Vagina (short section between uterus and cloaca).

The different parts of female gonoduct become modified in accor­dance with the modes of reproduction. In anu­rans, the uteri exhibit great modification. Bhaduri (1953) has classified the uterus of anu­rans into three broad categories (Fig. 7.45):

In Rana and Xenopus two uteri remain separate along their course and open into the cloaca by independent openings. This condition is called the uterus separatus. In Bufo and Rhino-derma a septum runs antero­posterior between two uteri, but posteriorly forms a common uterus by fusion at the terminal ends.

This condition is called uterus septatus. The two uteri have a common opening into the cloaca. The degree of fusion varies greatly and finally in Dendrobates, two uteri become con­fluent into an unpaired common uterus. The median partition wall between the uteri is absent.

This type of uterine condition is called the uterus communis. The uterus separatus is comparable with the duplex type, the uterus septatus with the uterus bipartite and uterus bicornis types and the uterus communis with the uterus simplex of the mammals.

Hermaphrodism, though occasional, is observed in adult amphibians. Hermaphro­dism occurs in adults as the consequence of failure of sex-directing mechanism to convert indifferent gonad into the specific sex. Because of dis-balance the anterior portion of the gonad remains as female while the posterior part becomes male. These two parts are usually separated by non-gonadal tissue bridge.

10. Reproduction and Development of Amphibians:

In majority of the amphibians, external fertilization is the rule. They are oviparous. But several instances of ovoviviparous condition are encountered. In Spelerpes fuscus, Typhlo­nectes compressicauda, Dermophis thomensis and Salamandra atra, the eggs are retained inside the oviduct where intra-uterine develop­ment occurs.

In most urodeles, the spermatozoa are transferred to the body of the female in the form of spermatophores. In almost all amphi­bians, the ontogenic development is indirect, i.e., accompanied by well-marked metamor­phosis.

Most of the amphibians undergo com­plete metamorphosis but some urodeles retain the larval features and become neotenic. The most remarkable instance of neotenous form is the Axolotl which breeds in larval state.

11. Reasons for Extinction of Amphians:

Amphibians are undoubtedly a neglected group as humans have a general tendency to dislike these creatures. They certainly deserve their share of attention as they perform a vital role in ecological balance and form an impor­tant link in the food chain. They also called “bio-indicator of pollution”.

The amphibian population throughout the world is decreasing alarmingly day by day. ‘The exact reasons for the declines are not known, though some local reasons are considered by her­petologists. We do not know the status of the Indian species as very little work has been carried out.

Habitat loss and alteration are the main threats to the amphibians. Breeding grounds are being altered at a fast rate, owing to the fill­ing up of the aquatic habitats for the construc­tion of modern complexes in the suburb areas of the cities and towns. Aquatic habitats are also being destroyed mainly by siltation and sewage contamination.

The forests are being rapidly converted to agricultural and cattle grazing purposes. Extensive use of insecticides and herbicides for agricultural purposes may be the reasons for amphibian declines.

The acid precipitation, and increased ultraviolet radiation are being linked to global declines. The reasons for amphibian vanishing are different in different countries. A brief discus­sion of the reasons of the declination in different countries is given here.

In Great Britain, the disappearance of some frog species with thermal pollution results from the hot effluents of nuclear power plant cooling systems. More frequently it is the chemical contamination that contributes to amphibian declines and disappearances. Progressive acidification of ponds has been responsible for the disappearance of numerous colonies of Bufo calamita in Great Britain.

General absence of amphibians of some regions of France and Belgium are extreme pollution by waste products, pesticides in agricultural zones, and heavy metals, etc. In Denmark Bombina bombina, Hyla arborea, Pelobates fuscus, Bufo viridis are declining fast than the previous years.

Holm Anderson (1995) described that a team of pro­fessional biologists resurveyed 1300 localities from 1977-1986. This survey revealed that 19% of the breeding ponds had disappeared but a further 40% had been altered to some extent. However, amphibians disappeared to a much greater extent than did the ponds about 50% of populations disappeared from 1945 to 1980.

In Hungary, Miklos Puky (1995) has stud­ied urban amphibian populations around Budapest since 1988, and has come to conclu­sion that marked declines in several species are due to both human impact and drought.

The annual meetings of Societas Europaea Herpetologica that held in Bonn, Germany in 1995 included a symposium on declining amphibian populations. T. Hayes of Berkeley, U.S.A. reported work on the role of oestrogen mimics as possible endocrine disruptors.

In Russia, Vladmir Ischenko of Ekatermburg (1995) suggested on the basis of skeleto- chronological studies of a number of species that short lived species may be more vulnera­ble to local extinction than long lived species.

The third Latin American Congress of Herpetology was held at the University of Campinas, Sao Paolo, Brazil, in December in 1993 and the researchers analysed the decline of Latin American amphibian species. They reported that Atelopus, Melanophryniscus, Dendrobates, Hylodes, Telmatobius, Batrachophrynus and Centrolene are extremely depen­dent on water bodies.

One of the reasons for local declines is overexploitation. Human con­sumption of Telmatobius arequipensis, T. marmoratus and Batrachophrynus macrostomum in Peru and Caudiverbera caudiverbera in Chile is depleting fast as compared with former large populations. Other reason is extraction and exportation as reported for Chile. In 1985, 236 anurans were reported, while in 1992, there was an exportation of 1,00,000.

Another reason given for declines is the introduction of non-native fauna. Xenopus lae­vis, Rana catesbeiana and Triturus sp. in many places over the Brazil, Peru and Chile and rain­bow trout (Oncorhynchus mykiss) along the Andes are seen as non-native faunas.

Less than 40 years ago, thousands of Amargosa toad (Bufo nelsoni), inhabited the Oasis valley in Southern Nevada, U.S.A. In 1994, this species consists of fewer than 100 individuals. Some of the factors believed to adversely affect the toad and its habitat include grazing, off road vehicle use, grading for flood control and modification by heavy equipment for the development of commercial enterprises.

The introduction and existence of non-native predators such as cat-fish and crayfish pollu­tion, and diversion of spring water have also directly affected toad populations. Three species of U.S.A. are in most danger and need of listing.

They are the Amargosa toad, the Western boreal toad (Bufo boreas boreas (Southern Rocky mountains popula­tions), and the great basin population of the spotted frog (Rana pretiosa). In addition the Wyoming toad (Bufo hemiophrys baxteri) could become extinct in the next few years.

Boreal toads (Bufo boreas boreas) experi­enced a massive die off in the Rocky Mountains of Colorado in the late 1970’s and early 1980’s. Red leg syndrome, caused by a variety of bacteria or fungi, has been identified as the proximal cause of death. Chytrid fungi are killing amphi­bians in the wild.

Recently the deaths of endangered boreal toads in the southern Rocky Mountains have been linked to a chytrid fungus, as also being responsible for amphibian die offs in Central America and Australia. Chytrid fungus in amphibians was first identified in 1998 by Green and other researchers from the U.S., Great Britain and Australia.

The Post Metamorphic Death Syndrome (PDS) is considered for the mortality of all or post metamorphic individuals in a short period of time. This disease agent may be the primary cause of certain amphibian declines in Northern West America. The proximal causes of death are usually widespread pathogens such as Aero monas (Red leg disease pathogen).

In Canada, factors related to human over­population, environmental contamination and habitat destruction have clearly been shown to be detrimental to amphibians, though the severity of the effect varies from species to species. In the North Eastern Greenland region, UV-B is linked to the amphibian declines.

It is considered a global phenomenon. The increased amount of ultra­violet radiation has reached the earth’s surface, as a result of destruction of ozone layer in stratosphere by the chemical pollutants, such as CFC and greenhouse effect.

The effects were confined at the poles at first, gradually are spreading into lower lati­tudes in both hemispheres. Ultraviolet light, in between 290-320 nanometer UV-B band, kills amphibian eggs and embryos.

In India, no sufficient work has done on the decline of amphibians. Maximum work has emphasised on survey.

K. Vasudevan (1998) reported the reasons of declines in Kalakad Mundanthurai Tiger Reserve, Southern India that the possible threat to amphibian species may be removal of top soil in large quantity by brick industries, and use of chemical fertilisers and pesticides, and human interference in the reserve forest which ultimately results in habi­tat loss.

From Bangladesh 13 species have been reported of which the population of Microhyla ornata, Microhyla rubra, Rana cyanophlictis, Rana hexadactyla and Rana tigrina are declin­ing fast for habitat destruction and use of insec­ticides.

In Vietnam 112 amphibian species have been recorded of which many species are valu­able economically and scientifically, have become rare.

Some are in danger of extinction or serious decrease such as Ichthyophis glutinosus, Paramesotriton deloustali, Bombina maxima, Rana chaepensis, Rana fansipani, Rana cancrivora, Rana kokchange, Rana tomanoffi, Rhacophorus appendiculatus and Rhacophorus nigropalmatus. The main reasons of declines are habitat destruction, overhunting and inappropriate exploitation.

Since the late 1970s, at least 14 frog species have declined or disappeared from rainforest areas of Queensland, Australia. The causes of the declines in Queensland’s upland rain-forest are still unclear. Recent work by Berger et al., (1998), however, indicates the possible involvement of a fungal pathogen in the declines.

No definite reason is considered for the decline of amphibian population, though different local reasons are forwarded in diffe­rent countries for the declines of population. A few years ago, acid rain, UV-B and parasites were the focusing points. The evidence now suggests that chemical contaminants should now be considered the most likely than the UV-B and parasites.

The US National Science Foundation (NSF) organised a workshop on amphibian declines in Washington DC, 28th and 29th May, 1998. Several speakers reviewed the latest informa­tion on the geography of amphibian declines.

It is clear from the reports that amphibians are continuing to decline worldwide, for a variety of reasons. The potential causes for declines are UV-B radiation, deformities, toxins, viruses, chytrid fungi, diseases in salamanders, climate changes arid immunology.

Lastly we can say that herpetofauna rep­resent a major part of our natural heritage. If these animals are in trouble, we are also in trouble. Amphibians and reptiles are the bio-indicators of the environmental pollution. If they decline and ultimately disappear, we need to make amends. What happens to her­petofauna is a sign of happening to other wild life and may be even to us.

FROGLOG, the bimonthly newsletter of the Declining Amphibian populations at the Department of Biology of The Open University. This news-letter helps to receive any news on amphibian declines at free cost.

In 1995 the Declining Amphibian Populations Task Force established an amphibian conservation forum, Amphibian Decline, on the internet. Subscribers of the forum may receive all e-mail sent to Amphibian Decline and may also send infor­mation that will be automatically distributed to other subscribers.

In 1989, the First World Congress of Herpetology was held in England and in a week-long discussion, it was known that amphibian populations that were once abun­dant, has become rare. The events that were isolated instances, gradually spread as a global pattern. In February, 1990, the scientists those were concerned about the vanishing amphibians, met at the West Coast Centre of the National Academy of Sciences.

In this conference it was known that amphibian populations were disappearing in different countries and often there was no apparent rea­son. Following that meeting an international effort was initiated to find out the causes of declines of amphibian populations by the Declining Amphibian Populations Task Force (DAPTF) of the Species Survival Commission (SSC) under the World Conservation Union (IUCN).

Now this effort is being conducted by the voluntary efforts of concerned herpetolo­gists. Regional Working Groups of the Task Force are monitoring the status of the amphi­bian populations in their areas.

At first different methods were adopted to monitor the declining amphibian populations, so a book — Measuring and Monitoring Biological Diversity : Standard Methods for Amphibians, published by Smithsonian University Press, Washington D. C. which contained standard methods for surveying declining populations.

In India several organisations are doing a good job in creating awareness among biolo­gists and common people for conservation of amphibians.

Froglog — the Newsletter of the Declining Amphibian populations Task Force — South Asia, the regional network of the Declining Amphibian populations Task Force, SSC, IUCN, is being edited by Sanjay Molur and Sushil Dutta, and published by Zoo Outreach Organisation and Conservation Breeding Specialist Group, India from PB 1683, 79 Bharathi Colony, Peelamedu, Coimbatore, Tamil Nadu, India.


Toad: Habitat, Structure and Life-History | Amphibians

In this article we will discuss about Toad:- 1. Introduction to Toad 2. Habit and Habitat of Toad 3. External Structures 4. Locomotion 5. Skeletal Structures 6. Coelom 7. Sense Organs 8. Vocalization 9. Life History 10. Enemy.

  1. Introduction to Toad
  2. Habit and Habitat of Toad
  3. External Structures of Toad
  4. Locomotion in Toad
  5. Skeletal Structures of Toad
  6. Coelom in Toad
  7. Sense Organs of Toad
  8. Vocalization of Toad
  9. Life History of Toad
  10. Enemy of Toad

Bufo melanostictus is a familiar example of toad. It is found in damp places all over this country. Toad represents a typical example of the class Amphibia. Despite the fact that toad is a highly specialised form amongst the living amphibians, it is studied extensively to gain an elementary knowledge on the anatomy of vertebrates in general and an amphibian in particular.

According to Duellman and Trueb (1986)

Subphylum – Vertebrata (Craniata)

Scientific Name Bufo melanostictus Schneider, 1799.

English Name Common Indian Toad:

Oriya – Katkatia Benga, Luni Benga, Kuji Benga

2. Habit and Habitat of Toad:

Toad is a cold-blooded or poikilothermous or Exothermic i.e., the temperature of the body depends on the temperature of the external environment) vertebrate. During col­der months of the year toads undergo through a phase, called hibernation or winter sleep. An adult toad generally lives on land, but if necessary it can live in water for some time.

It is truly an amphibian both in biological as well as well as literal sense (amphi= both bios = life). Toad is quite at home in water as well as on land. On land it is obligatory for the toad to remain in dark and moist places, preferably near water. Skin of toad is an accessory respi­ratory organ and so it is kept moist. It tries to keep itself away from bright light.

Toad is a carnivorous animal and catches insects by its sticky tongue. Toads are noctur­nal and usually come out of their hides at dusk. The males can produce croaking sound by the help of the vocal sac, specially during breeding season.

Toad lives on land but breeds in water. All the organ systems of toad are adjusted to land life except the reproductive system. For the purpose of reproduction it had to go back to the primal aquatic abode.

3. External Structures of Toad:

Toad has a short bilaterally symmetrical body (Fig. 7.2). There is no exoskeleton over the skin, i.e., the skin is naked. The skin is rough is texture. The dorsal side of the body is blackish-grey while the ventral side is yel­lowish grey.

Toad can change the colour of the body to match with the hues of its sur­roundings. Ordinarily, its body colour is same as that of the earth. The body is divisible into head and trunk. Distinct neck is absent. A postanal tail is absent in adult stage. The tail is present and well-developed in the larval condition. The head is semicircular in out­line. It is broad, depressed and has a blunt snout.

The mouth is a wide opening located at the terminal end of the head. At the anteri­or dorsal side of the head there is a pair of rounded openings, known as nostrils or external nares. The eyes are very large and prominent. These are protruding and are situ­ated one on either side of the head. Each eye is provided with a thick upper eyelid and an ill-developed lower eyelid.

A transparent nictitating membrane (or third eyelid) is pre­sent and it is stretched to cover the eye ball. Behind each eye, a circular area, known as eardrum (or tympanum), is present. Just behind each tympanum there is an elongated elevation, called Parotoid gland. These paired glands secrete a whitish, pungent and sticky juice.

It is a poisonous secretion and causes nausea and affects the heart in man, if swallowed. When the secretion falls in the eyes and nose, it causes irritation, but rarely affects the skin. These glands act as the organs of offense and defence. The skin on the floor of the buccal cavity becomes inflat­ed to form vocal sac in males.

The trunk is broad, short and flattened. Numerous small elevations, known as warts, are present on the dorsal side of the body. The cloacal aper­ture or vent is located on the dorsal side of the posterior end of the body between the two hind limbs. There are two pairs of limbs. These are of unequal size. The forelimbs are smaller than the hind limbs.

Each forelimb consists of brachium (upper arm), and ante- brachium (forearm), a wrist and a manus (hand). The hand is followed by four digits. In male individual, a cushion like thumb pad (or nuptial pad) develops during breeding season at the basal part of inner finger.

These pads facilitate the male’s grip during amplexus. The hind limbs are strongly built and are much longer than the forelimbs. These two limbs are modified for jumping and swimming.

Each hind limb is composed of a proximal sector, called femur (thigh), which is followed by crus (shank). Distal to the shank lies the pes (foot). The foot consists of a long tarsal region and five elongated slender digits. The digits are united by webs which help in swimming.

The skin of toad is kept moist and fre­quently slimy. Besides its protective function, the skin of toad serves as an additional respi­ratory organ. During hibernation, toad respires entirely by the skin. The skin is composed of an outer epider­mis and an inner dermis (Fig. 7.3).

These two layers are separated by a basement membrane and a fibrous layer containing the chromatophores or pigment cells. The epidermis is a compound structure and is made up of several layers. The outermost layer is called stratum corneum. It is a thin, scaly and corn­field layer.

This layer is dead and is shed peri­odically. This phenomenon of periodic shed­ding of the stratum corneum is called ecdysis (or moulting). In other amphibians, the stratum corneum is thin and delicate, while in toad it is thicker and heavily cornfield. The innermost layer of the epidermis is composed of colum­nar cells with prominent nuclei.

This layer is called stratum germinativum (or Malpighian layer) which sits on the basement membrane. The cells lying between the stratum germina­tivum and stratum corneum constitute the transitional layer. These cells form several lay­ers and decrease in size from below upwards.

The dermis is thicker than the epidermis and is divisible into two layers. The outer layer accommodating most of the glands is called stratum spongiosum. This is composed of loose network of connective tissue matrix with blood vessels and lymphatic spaces. The superficial part of this layer contains the pigment cells.

The innermost layer is called stratum compactum which is composed of dense connective tissue, smooth muscle fibers, nerves and blood vessels. Beneath the stratum compactum lies a loose subcutaneous connective-tissue layer containing fatty tissue.

The skin of toad is marked by the presence of numerous bumps (or warts) all over the dor­sal body surface. These warts may be either due to underlying poison glands or sensory papillae. There are two types of skin glands in toad.

(a) Mucous glands secreting mucus and

(b) Poison glands producing poison.

The mucous glands are smaller than the poison glands. The poison glands are composed of granular secretary cells. The skin glands usually lie in the stratum spongiosum of the dermis, but the poison glands may be more deeply located. These glands are unsheathed by connective and muscular tissues, which help in squeezing the secretory products. The products of the gland come out through duct to the outside.

The colour of toad depends upon the pre­sence of pigment cells or chromatophores in the dermis. Some chromatophores also invade the epidermis. Depending on the types of con­tained pigment granules, the chromatophores may be melanphores (containing black pig­ment), guanophores (containing colourless crystals of guanine) and lipophores (contai­ning yellow pigment).

The melanophores are situated in the deepest layer, the guanophores are intermediate in position while the lipophores are present in the upper layer. The melanophores are responsible for the produc­tion of blackish colour and the lipophores cause yellowish effect. The guanine crystals in the guanophores produce diffraction effect.

The colour change in toad is rather a slow pro­cess and is controlled under the action of melanophore stimulating hormone (MSH) of the pituitary gland. The colour change in toad is not under nervous control. In fishes, instanta­neous colour change is caused through the nervous system while the slower change is under hormonal control.

4. Locomotion in Toad:

In toad, the entire muscular and skeletal systems have become specialised for jumping and swimming. The movements are caused by the thrust of both the hind limbs. The move­ments are caused by the thrust of both the hind limbs. Besides jumping and swimming, toad is able to walk on land. This is caused by bringing into play a set of proprioceptor reflexes.

In resting state, the anterior part of the body is supported by the hind limbs. The hind limbs are folded in the manner of ‘Z’. From such a sitting or squatting posture, toad jumps by a sudden extension of the hind limbs.

The forelimbs manipulate and adjust the direc­tion before each jump. Swimming is done by the activity of the limbs which act as the pro­pellers. The hind limbs are long and the digits are webbed. These limbs act like oars and enable the animal to swim.

5. Skeletal Structures of Toad:

There is no exoskeleton in toad. The skele­ton that supports the soft parts lies internally and is designated as endoskeleton. It is chiefly made up of bones and cartilages. These two structures are associated with one another to form the internal framework.

The endoskele­ton is described under two broad heads:

(b) The appendicular skeleton.

The axial skeleton comprises of the skull and the vertebral column.

The skull of toad is flat and broad. It contains a tubular cranium and is pierced pos­teriorly by a large aperture, called foramen magnum. Through this aperture the spinal cord passes. On each side of this foramen there is an exoccipital bone which bears a convex occipi­tal condyle. So there are two occipital condyles which fit into the two concavities of the first vertebra.

The occipital condyles are developed from the exoccipitals. The roof of the cranium is made up of two flat bones, called the front parietals. Each frontoparietal is formed by the fusion of two bones, the frontal and pari­etal (Fig. 7.5A).

The floor of the skull is formed of a dagger-like Para sphenoid. A ring-like sphenethmoid bone is present at the anterior end of the cranium. This bone is completely covered by front parietals on the dorsal side. The nose is covered dorsally by a triangular nasal bone and the floor is provided with the vomer (Fig. 7.5B).

The cartilaginous otic cap­sules are loosely attached with the cranium. The auditory capsules are situated in front of the exoccipitals. The floor of the auditory cap­sule is supported by the lateral extension of the Para sphenoid and the dorsal side is covered by prootic bone. A small hammer-like squamosal connects the posterior part of the upper jaw with the otic capsule.

Each half of the upper jaw is made up of small premaxilla, long slen­der maxilla and quadratojugal. Behind the quadratojugal there is a very small Y-shaped supporting bone, called the quadrate. The other two supporting bones are the pterygoid and the palatine. The palatine is rod-like and connects the maxilla with the sphenethmoid bone.

The lower jaw is composed of two halves and the halves are united anteriorly by ligament (Fig. 7.6A). Each half is developed from a Meckel’s cartilage and consists of three bones, the dentary, angulosplenial and mentomeckelian. The posterior part of the angulos­plenial articulates with the upper jaw. Both the upper and lower jaws are toothless in toad. In frogs the upper jaw besets small conical teeth.

The hyoid apparatus is essentially a cartilaginous structure which sup­ports the floor of the buccal cavity (Fig. 7.6B). It also forms the supporting frame-work for the attachment of the tongue. The body of the hyoid constitutes the main bulk of the appara­tus.

There are two pairs of prolongations (or horns) from the body of hyoid apparatus. The anterior pair are longer and extend up to the auditory capsules. These are called anterior cornua.

Similar pair on the posterior side are known as posterior cornua which enclose the laryngotracheal chamber.

The vertebral column (Fig. 7.7A) is composed of nine vertebrae and a terminal rod-like structure, called urostyle (oura=tail and style=rod).

A typical vertebra has a solid cylindrical part, known as centrum. The centrum is procoelous, i.e., the centrum is concave anteriorly and convex posteriorly (Figs. 7.7 C1, C2). On the dorsal side, the cen­trum bears a ring-like neural arch which encloses the neural canal. The roof of the neu­ral arch possesses a median elevation known as neural spine. In the lateral side the neural arch carries transverse processes. The articula­ting processes are present on the neural arch.

The anterior pair of processes are known as prezygapophyses and the posterior pair are called postzygapophyses (singular—postzygapophysis). All the vertebrae excepting the first and the last one have typical structural construction. But in frog, the eighth vertebra is provided with amphicoelous central, i.e., both the ends of a centrum are concave.

First vertebra or atlas:

It articulates with the occipital condyles of the skull. It is ring-like in appearance (Fig. 7.7B). The transverse pro­cesses and the prezygapophyses are absent. Anteriorly it possesses two concave facets which fit with the paired occipital condyles of the skull. The centrum is greatly reduced.

This vertebra is peculiar and has two-rounded condyles on the poste­rior side of the centrum for articulation with the anterior paired concavities of the urostyle. The transverse processes are stout, fan-shaped (Fig. 7.7 D1, D2) and articulate with the pelvic girdle. The postzygapophyses are absent. The ninth vertebra is also known as sacral verte­bra. In frog, the transverse processes are not fan shaped but are cylindrical.

The urostyle is a long slender rod-like structure (Fig. 7.7 E1, E2) and is formed by the fusion of a number of vertebrae.

It has a pair of concave cavities at its anterior end for articulating with the paired posterior convexi­ties of the ninth vertebra. It has a mid-dorsal neural crest. A very narrow hole is present throughout the urostyle which represents the reduced neural canal. Through this canal passes the filum terminale of the spinal cord.

Appendicular skeleton:

The skeletal frame of the paired limbs and the girdles constitute the appendicular skele­ton (Fig. 7.8).

The pectoral girdle consists of two symmetrical halves. These halves are united at the mid-ventral line but are free dorsally (Fig. 7.8B). This girdle forms a bony framework for encircling the anterior part of the trunk. Each half of the pectoral girdle is made up of a broad dorsally placed and partly cartilaginous plate like structure, known as suprascapula.

Attached to it, there is a strong bone, called scapula. Two rod-like bones are connected with the scapula. The anterior one is called clavicle, while the posterior one is known as coracoid. The clavicle encloses the precoracoid cartilage which is hardly visible. The clavicle and the coracoid are joined with partly overlapping pieces, the epicoracoids.

The space present between these three bones is designated as coracoid fontanella. Just at the junction of the clavicle, coracoid and sca­pula there is a cup shaped depression, called glenoid cavity, into which the head of hume­rus fits. Projecting posteriorly from the united posterior end of the epicoracoid there lies a sternum which has a terminal flattened carti­laginous xiphisternum.

The pelvic girdle is a V- shaped bony structure having a disc-like pos­terior end. The disc is formed by the union of three bony units on each side, the ilium, ischi­um and pubis (Fig. 7.8D). A cavity known as acetabulum is present on each side of the disc. The head of femur fits into this cavity.

The ilia are elongated curved rod-like struc­tures which are attached with the transverse processes of ninth vertebra. They form the anterior and dorsal sectors of the disc. Two pubes (Singular—pubis) are represented by a triangular cartilage on the ventral side of the disc. The posterior sectors of the disc are formed by the ischium.

There are two forelimbs and each forelimb is composed of several long bones arranged end to end (Fig. 7.8A). The first one in the series is called humerus whose mid­dle region is slightly curved. The proximal end is termed as the head of the humerus which fits with the glenoid cavity of the pectoral girdle. The distal end carries a pulley-like trochlea.

A prominent crest, called deltoid ridge, is exten­ded from the head to the middle region of the humerus. The second in the series is the radio- ulna formed by the fusion of two separate bones, radius and ulna, the anterior end of the radio-ulna is concave and fits with the trochlea of the humerus. The proximal end is drawn out into an olecranon process.

The distal end is flattened to give attachment of six carpal bones which are arranged in two rows. Four slender rod-like bones, called meta­carpals, are connected with the digits. There are four digits. The third and fourth digits have three phalanges and the first and second have two phalanges.

The hind limbs, like the fore­limbs, are also paired structures. Each is made up of series of long bones (Fig. 7.8C), The proximal one is the femur which is gently curved. The anterior end of the femur is round­ed to form the head of the femur and the pos­terior end is slightly flattened to form the condyle. The next part is known as tibiofibula formed by the fusion of two bones, the tibia and fibula.

Both the ends of the tibiofibula are expanded to give articulation with the condyle of the femur anteriorly and with the tarsal bones distally. The tarsal bones are arranged in two rows. The proximal tarsals are the astra­galus and calcaneum. These are elongated structures and are slightly curved outward. Both the astraglaus and calcaneum are joined with one another at both ends.

The distal tarsals are composed of two or three small bones. The foot is constituted of five metatarsals. There are five digits having vari­able number of phalanges.

The first and sec­ond digits have two phalanges, the third and fourth have four phalanges and in the fifth there are three phalanges. A bony projection made up usually of two small bony nodules is present on the outer side of the hallux. This structure is known as the pre-hallux or calcar.

The coelom is a large and undivided cav­ity. The internal organs or viscera are lodged in the coelom. The coelom is lined by the coelomic epithelium, called peritoneum. The peritoneum also encircles the alimentary canal and other organs.

These visceral organs are suspended to the body wall by fan-shaped folds, called mesenteries. The pericardial cavity housing the heart is a coelomic deri­vative which becomes cut off from the main coelom and exists as a separate cavity to house the heart.

The sense organs are the receptors for external stimuli. These are the avenues through which the central nervous system is kept informed of the outside world. Each receptor organ can respond to a particular type of stimulus and produces its own specific sensation.

Receptors for cold, heat, pain and touch are present beneath the epidermis of the skin. These are microscopic in structure and are usually regarded as cutaneous receptors.

These receptors are scattered in the nasal passage. The mucous membrane lining the nasal passage contains peculiar olfactory cells and slender supporting cells. The olfactory cells are connected with nerve fibres from the olfactory nerve and are the actual receptors for smell.

The taste buds present in the tongue and mouth cavity are the recep­tors for taste. Each taste bud is made up of two types of cells, the taste cells and the support­ing cells. The taste buds are located in the tongue in association with minute elevations called papillae.

The eyes are the two very compact photosensitive organs. These organs are lodged in the orbits. Each eye has a spherical body and is usually called eye ball. The eye ball can be rotated inside the orbit within its limit by six extrinsic muscles.

The eye can be protruded by the levator bulbi and can be withdrawn by the retractor bulbi to a certain limit.

The eye ball is composed of three layers arranged in a regular sequence (Fig. 7.21 A).

This is the outer­most layer of the eye ball. It is very tough and thick. It consists of two parts: An anterior trans­parent circular portion, called cornea and an opaque posterior portion, called white of the eye ball. The cornea permits the entry of light rays inside the eye.

The outer surface of the cornea is covered by a thin transparent mem­brane, called conjunctiva. The sclera is com­posed of cartilage and fibrous tissue and gives protection to the delicate parts of the eye.

(b) Uvea or middle layer:

This layer is divided into three parts:

The choroid part is a highly vascular pigmented layer. At the ante­rior end and just behind the cornea, the choroid is modified to form a circular pigmen­ted disc, called iris. The iris contains an aperture at the centre which is known as pupil.

The iris acts as a diaphragm and contains circular and radial muscle fibres which help the pupil to contract or dilate. Excepting the pupil, the eye ball is totally light-proof. The iris regulates the entry of light into the eye ball. Just behind the iris, there are suspensory ligaments which keep the lens in position.

The retinal layer forms the innermost and the light sensitive screen of the eye. It contains two types of photosensitive cells, called rods and cones. The cones are primarily concerned with the colour vision in bright light and the rods are chiefly useful in colourless vision at low light intensities. The photosensitive cells are connected with the nerve fibres of the optic nerve.

A crystalline lens is situated just behind the pupil and is kept in position by suspen­sory ligament. The lens divides the cavity of the eye into two chambers. The anterior cham­ber between the lens and the cornea is filled up with a watery fluid, the aqueous humor and the posterior one behind the lens is filled up with a transparent jelly-like substance, the vitreous humor.

Just at the point of entry of the optic nerve into the retinal layer there is a depression, known as blind spot, where no image is formed. Two muscles, one dorsal and the other ventral, are connected with the sus­pensory ligament of the lens and with the cornea.

These muscles are known as protrac­tor lentis. Contraction of the protractor lentis draws the lens closer to the cornea and when relaxed the lens is pushed away from the cornea.

Light rays, on the way through cornea, pupil and the lens, are con­verged to the retinal layer. In the retinal layer an inverted and reduced image is formed which is transmitted to the brain via the optic nerves. This inverted image is translated into a corrected one by the brain. Adjustment of the image (accommodation) on the retinal layer is done by the forward and backward move­ments of the lens by the protractor lentis.

The photochemical basis of image for motion relates that the vision depends upon the photosensitive pigments present in the photosensitive cells. Visual purple (rhodopsin) is abundant in the rods and visual violet (iodopsin) is present in the cones.

The synthe­sis of both these pigments depends upon the presence of vitamin A. The pigments are decomposed by the light and various products are produced which can create impulses in the photoreceptor cells of the retina.

Two types of vision are encountered in animals one is the binocular vision which means that the two eyes can be focused on the same object and the other is the monocu­lar vision when each eye has a different visual field. In toad, the vision is monocular, because eyes laterally placed and cover different visual areas.

Receptors for hearing and balancing:

The ears sub-serve dual functions, hearing and balancing. The ear of toad consists of three parts: the external ear, the middle ear and the internal ear. The external ear is represented by a tightly stretched membrane, called tympa­num. The middle ear is a tube like cavity. The cavity of the middle ear is in communication with the buccal cavity by Eustachian tube.

Presence of the eustachian tube equalised the atmospheric pressure on the two sides of the tympanum. A bony rod, the columella con­nects the tympanum with the membranous par­tition separating the middle and the internal ear. The internal ear is represented by the membranous partition separating the middle and the internal ear.

The internal ear is repre­sented by the membranous labyrinth which is enclosed by the auditory capsule (Fig. 7.21 B). The membranous labyrinth floats in a fluid, known as perilymph and the cavity of the labyrinth is filled with another fluid, known as endolymph. The auditory capsule is sealed from all sides by a membranous partition. Membranous labyrinth is made up of two chambers. The upper chamber is called utriculus and the lower one is the sacculus.

The utriculus gives out narrow tubular semicircular canals (Fig. 7.21C). There are three semicircu­lar canals, one is horizontal in position and the other two are vertically disposed. All the three semicircular canals are arranged at right angles with one another. Both the ends of the semicir­cular canals open into the utriculus. Each canal bears an ampulla at its one end only.

The sac­culus produces a short projection, called lagena. Patches of sensory receptors are present in the inner wall of the membranous labyrinth. Each patch is composed of sensory cells and supporting cells. Receptor cells are connected with the nerve fibres from the auditory nerve.

Sound waves direct­ly impinge upon the tympanum and the vibra­tions are conveyed by the columella to the perilymph. From the perilymph, the vibrations are carried to the endolymph and thus stimu­late the sensory cells of the sacculus and lagena. The impulses are transmitted to the brain through the auditory nerves and are per­ceived as sound in the brain.

Mechanism of balancing:

The semicircular canals maintain the equilibrium of the body. Calcareous particles (otoliths) present inside the semicircular canals strike upon the bristles of receptor as the animals lose the balance. Besides, the semicircular canals are arranged in such a fashion, that these can easily detect changes of the centre of gravity during move­ment.

According to Noble (1931), the voice of toads and frogs is to attract mates. Wellman (1917) observes that in case of American Toad, the voice of male has a strong influences in attracting of the females. The vocalization of male Bufo melanostictus can be classified into 2 types.

a. Advertisement call:

Before amplexus, one of the males begins to croak with low-pitch which is quickly followed by some other males in the breeding site area. This call con­tinues until the females approach closely. The call is made up of a series of identical notes.

During amplexus, males often produce a guttural croak with high pitch whose duration is very short.

Territorial calls func­tion as spacing mechanisms among males and are most common among species that have prolonged breeding seasons. In B. melanostictus (Fig. 7.24), one of the males begins a single note call, is followed quickly by other males in the same breeding ground area, to form a chorus.

If one of the croakers stops, others will gradually stop their croaking. This call is used as advertise­ment to attract the females for mating.

Common toads (B. melanostictus) when escape from their enemies, rarely croak or chirp. But when their predators like snakes try to swallow by seizing their hind legs or mid­dle part of body, they produce a screaming sound.

9. Life History of Toad:

Many amphibians maintain a typical biphasic life-history pattern. Adults visit to breeding ponds, deposit eggs, and return to terrestrial habitats. The life-history of toad is very much complicated and may be discussed in follow­ing points.

Breeding habits:

Breeding of Bufo melanostictus takes place from December to September coinci­ding with the pre-monsoons, monsoons and post-monsoons. Heyer (1973) mentioned that the highest reproductive activity takes place at the beginning of the rainy season.

After a heavy shower of rainfall, the males call can be heard at the bank of ponds, ditch­es and near a stagnant rain water pool of the land. Mating call could be defined as a short peep.

On hearing the mating call, the female approaches, several males scramble around her and begin to ride on the back of the female. But most of them become unsuccessful due to their joint struggling to ride. Lastly, one of them becomes successful and holds-firmly by his fore and hind limbs (Fig. 7.25).

When axillary amplexus begins, the female moves in the water for egg laying. During the breeding season sexual dimorphism is prevalent. Males possess black vocal sac and nuptial thumb-pad at each ironer most finger of the hand. McCann (1928) reported one instance of amplexus in captivity which was continued for 21 days. Daniel (1963) observes that the species is a prolific breeder.

A single female may lay over a thousand eggs in any convenient patch of water. Several workers have reported that amphi­bian breeding season in India and other tropical countries is normally between May and August (during the monsoon period). But the author of 6th edition has observed that the breeding of Bufo melano­stictus takes place in winter months (December-January) in Southern Bengal if rain happens.

Structure of germ cells:

The eggs are sphe­rical cells. Each egg has a blackish animal pole and a whitish vegetal pole. The animal pole is full of protoplasm and the vegetal pole is full of yolk. Such a type of egg is called telolecithal type. Each egg is surrounded by vitelline membrane.

The egg gets a coating of jelly-like albumen while passing through the convoluted part of the oviduct. The spermato­zoa are highly specialised cells with an oval head containing nucleus, a short neck having centrosome and a long wavy protoplasmic tail.

Union of male and female gametes takes place externally, i.e., ferti­lization is external. The female toads lay their pigmented eggs in quiet water inside the weeds or around the stem, leaves within a translucent slimy tube, and the male discharge their spermatozoa or milt over the eggs as they are expelled.

Daniel (1963) reported that in the absence of plants the eggs are laid in long strings at the bottom of the pond or stream.

The outer membrane of the egg gives an impasse to one sperm after which the outer membrane becomes impervious to other sperms. Only the head portion of the spermatozoa enters into the cell-body of ovum and the tail is left out.

The sperm nucleus is called male pro-nucleus, and the egg nucleus is known as female pro-nucleus. During fertilization, the male and female pronuclear fuse to form a single nucleus. The egg, thus fertilized, is known as Zygote.

Embryonic development:

The zygote undergoes rapid divisions known as cleavage (or segmentation) and results in the production of a large number of blastomeres (Fig. 7.26). The cells now arrange to form a cellular ball, known as blastula.

Now the blastula enters into a complicated stage, known as gastrula and the process is known as gastrulation. The gastrulation is essentially a process of cell movement when the different cells take up their respective position for future differen­tiation.

During this process three primary germinal layers:

(c) Endoderm are differentiated.

All the structures of the adult are developed out of these three primary germinal layers. After about two weeks a small embryo is seen moving and wriggling. The developing embryo gets nourishment from the yolk and eventually hatches as the tadpole larva.

The larvae spend in aquatic medium for various amounts of time depending on hydro period, thermal range, predation, competition and other related factors. Fig. 7.27 illus­trates the larval development and metamor­phosis of toad.

Their main enemies are birds, and the snakes – the greatest enemies in India are striped keelback (Amphiesma stolata), check­ered keelback water snake (Xenochropis piscator), rat snake (Ptyas mucosus), Indian spectacled cobra (Naja naja naja), saw-scaled viper (Echis carinatus), Indian monoceled cobra (Naja naja kaouthia) and flying snake (Chrysopelea ornata).

The wheels of bicycles, rickshaws and automobiles may be considered a great enemy of the toads. The recent but most dangerous – the effluents of industries are destroying their breeding grounds, their larvae and the abodes of their adults.

The population is gradually declining, though not alarmingly in the country. Due to heavy use of insecticides, filling up of the breeding grounds for human habitation, sewage pollutants, conversion of low land plots and small water bodies for housing deve­lopments, their breeding sites are on the way of destruction.

Another major factor is the use of B. melanostictus in the school and college laboratories for dissection purposes. In this connection, thousands and thousands of toads are killed every year in India.

These causal factors are also responsible for the decline of population in Rana tigerina and R. hexadactyla. It was estimated that in 1979 India earned 4.7 million dollar from the export of frog’s legs (Rana tigerina and R. hexadactyla), despite the ban on the export of frog’s legs in 1977 by the Indian Government.

As an adult frog and toad con­sume mostly insects, approximately its own weight every day, it can be estimated that 5,000 tonnes of toads and frogs would eat about 4,50,000 tonnes of food, mainly insects in over 90 days period.

So it can be conclu­ded safely that the killing of vast number of toads and frogs must lead to an innumerable increase in- the pest population. The insecti­cides are then used to the insect infected crops, which in turn pollute environment and upset the ecological balance.


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We acknowledge the Traditional Owners of the land, sea and waters, of the areas that we live and work on across Australia. We acknowledge their continuing connection to their culture, their contribution to our shared knowledge, and pay our respects to their Elders past and present.


Biology Chapter 11, 12, 13, 14

Mutations by themselves are rarely the cause of evolution in populations of plants and animals because:

Large antlers in male elk, which are used for battles between males, are a good example of

Genetic differences between populations tend to be reduced by

Mate-attracting features such as the bright plumage of a male peacock result from

A change in the relative frequencies of alleles in the gene pool of a population is called

A random change in an organism’s DNA

Certain whale species were hunted to near extinction. With a moratorium on hunting them, their population sizes have expanded. Which of the following is true?

The populations may still be endangered because they may have little remaining genetic variation

What is the result of natural selection?

a change in the gene pool of a population due to differential reproductive success

Which of the following provides evidence that vertebrates evolved from a common ancestor?

All of the choices are correct: similarities in protein structure, common development of pharyngeal pouches, homologous structures, the presence of similar genes

Which one of the following is false? Natural selection

Results from an organism’s needs

Which one of the following is false?

All variation in a population is heritable

Natural selection is often described as "survival of the fittest" The best measure of an organism’s fitness is

How many offspring it produces

Which of the following promote(s) genetic variation in a population?

All of the choices promote genetic variation in a population: balancing selection, heterozygote advantage, frequency-dependent selection

Analogous structures found in two species are structures that have

Similar overall shape due to common function

Which one of the following was not a main idea that Darwin advanced in his works?

New species can form by inheritance of acquired characteristics

The term macroevolution refers to which one of the following

Grand scale of evolution over many geological time

The unifying theme of biology is

Tay-Sachs is inherited as an autosomal recessive allele. Homozygous individuals die within the first few years of life. However, there is some evidence that heterozygous individuals are more resistant to tuberculosis. Which of the following statements is true?

This situation is an example of heterozygote advantage

Which one of the following represents two structures that are homologous?

The wing of a bat and the flipper of a whale

Long-legged cheetahs are well adapted to catching prey. The ancestor of the cheetah is believed to have had relatively short legs. According to Darwinian views, the evolution of long-legged cheetahs is best explained by

A plant breeder has been trying to develop a strain of snap dragons with blue flowers from a population of snapdragons some of which have white flowers and some of which have blue flowers. He finds that no matter how careful he is to only select blue flowered snap dragons, when he plants them out side roughly 10% of the snapdragons have white flower and some plants have both blue and white flowers on the same plant. The most likely explanation is:

Selection can only act on heritable variation and the white flower is due to environment

Mutations by themselves are rarely the cause of evolution in populations of plants and animals because:

Which of the following assumptions was not part of Darwin’s theory of natural selection?

Traits are inherited as discrete particles

Fitness increases when an organism

passes on a greater proportion of its genes to the next generation

The disease phenylketonuria (PKU. is caused by a recessive allele, and one child in 10,000 is born with the disease. Let q represent the frequency of the PKU allele. What is the value of q2? (Fetuses with PKU are no likelier than other fetuses to die before birth..

A population of 1,000 birds exists on a small Pacific island. Some of the birds are yellow, a characteristic determined by a recessive allele. The others are green, a characteristic determined by a dominant allele. A hurricane on the island kills most of the birds from this population. Only ten remain, and those birds all have yellow feathers. Which of the following statements is true?

The hurricane has caused a population bottleneck

What term is used to refer to structures that have a similar origin or ancestry even though they may be very different in appearance?

In a cell in which 2n = 6, the independent assortment of chromosomes during meiosis can by itself give rise to __________ genetically different gametes

the smallest unit that can evolve

The core theme of biology is

Species are fixed (permanent) and perfect

More than they resembled animals on ecologically similar but distant islands

Darwin found that some of the species on the Galapagos islands resembled species of the South American mainland

Descent with modification occurs through inheritance of acquired characteristics

Which of the following statements would Darwin have disagreed with?

Earth’s surface is shaped by natural forces that act gradually and are still acting

Lyell’s book Principles of Geology, which Darwin read on board the H.M.S Beagle, argued in favor of which of the following concepts?

The tendency to bark is not a heritable trait

A dog breeder wishes to develop a breed that does not bark. She starts with a diverse mixture of dogs. Generation after generation, she allows only the quietest dogs to breed. After 30 years of work she has a new breed of dog with interesting traits, but on average, the dogs still bark at about the same rate as other dog breeds. Which of the following would be a logical explanation for her failure?

Whether an organism survives and reproduces is almost entirely a matter of random chance

Which of the following assumptions or observations contradicts Darwin’s idea of natural selection?

Differential reproductive success based on inherited characteristics

Which of the following best expresses the concept of natural selection?

Who developed a theory of evolution almost identical to Darwin’s?

Natural selection starts with the creation of new alleles that are directed toward improving an organism’s fitness

Which of the following statements regarding natural selection is false?

It is fully decomposed by bacteria and fungi

Which of the following statements regarding the currently available fossil record is false?

The currently available fossil record shows that the first life forms were eukaryotes

Which of the following statements regarding the currently available fossil record is false?

Which of the following disciplines has found evidence for evolution based on the native distributions (locations) of living species?

Humans share several features with salamanders. Certain genes and proteins are nearly identical between the two species both species have four limbs with a similar skeletal structure the species’ early embryos are very similar and where the salamander has a functional tail, humans have a vestigial tailbone. In evolutionary terms, these are examples of

Relatively ancient common ancestors…relatively recent common ancestors

Deep branch points near the base, or truck, of an evolutionary tree represent ______, while branch points near the tips of the branches represent ______

A change in allele frequencies within the gene pool of a population

Which of the following would a biologist describe as microevolution?

Have the potential to interbreed in nature and produce fertile offspring

A biological species is defined as a group of organisms that

Organisms that possess more than two complete sets of chromosomes are said to be

10 to 20 billion years ago

The "big bang" that produced the universe is though to have occurred

The earliest discovered fossils are of ______ dating back to ______ years ago.

The atmosphere was rich in gases released in volcanic eruptions volcanic activity, lightning, and ultraviolet radiation were all much more intense than on today’s Earth

When the Earth first solidified, what were conditions like?

A group of individuals of the same species living in the same place at the same time

A population’s allele frequencies change over a span of generations

Microevolution, or evolution at its smallest scale, occurs when

Mutation in parent cells (asexual organisms) or in cells that produce gametes (sexual organisms)

The ultimate source of all new alleles is

Heritable traits that promote reproduction become more frequent in a population from one generation to the next

Which sentence best describes the true nature of natural selection?

She should continue taking the drug until her immune system can completely eliminate the infection. Otherwise the remaining bacteria in her system may recover, and they will probably be resistant

A woman struggling with a bacterial illness is prescribed a month’s supply of a potent antibiotic. She takes the antibiotic for about two weeks and feels much better. Should she save the remaining two-week supply, or should she continue taking the drug?

A harmful allele in an asexual, haploid population

Which of the following would most quickly be eliminated by natural selection?

A northern landmass called Laurasia and a southern landmass called Gondwana

When the continent of Pangaea first split apart, it formed

Classify species in groups that reflect evolutionary relationships

Ever since Darwin, systematics has tried to

Only within the domain Eukarya

In the three-domain system, the eukaryotes are represented

Subdivides the prokaryotes into two different domains

Organisms have evolved over time…beginning with the formation of molecules…then the molecules formed organisms…and those organisms formed more complex organisms

There are numerous theories of evolution with the common thought

God is the creator of all

There are numerous theories of creation with the common thought

There is a higher, intelligent being that made all that we see today (Irreducible Complexity)

Another way of explaining our origin is intelligent design with the common thought

A base substitution mutation in a gene does not always result in a different protein. Which of the following factors could account for this?

e. the fact that some amino acids are specified from more than one codon

Darwin found that some of the species on the Galápagos islands resembled species of the South American mainland

B) more than they resembled animals on ecologically similar but distant islands.

Who developed a theory of evolution almost identical to Darwin’s?

During the 1950s, a scientist named Lysenko tried to solve the food shortages in the Soviet Union by breeding wheat that could grow in Siberia. He theorized that if individual wheat plants were exposed to cold, they would develop additional cold tolerance and pass it to their offspring. Based on the ideas of artificial and natural selection, do you think this project worked as planned?

C) No, because there was no process of selection based on inherited traits. Lysenko assumed that exposure could induce a plant to develop additional cold tolerance and that this tolerance would be passed to the plant’s offspring.

Broccoli, cabbages, and brussels sprouts all descend from the same wild mustard and can still interbreed. These varieties were produced by

Which of the following best expresses the concept of natural selection?

A) differential reproductive success based on inherited characteristics

A dog breeder wishes to develop a breed that does not bark. She starts with a diverse mixture of dogs. Generation after generation, she allows only the quietest dogs to breed. After 30 years of work she has a new breed of dog with interesting traits, but on average, the dogs still bark at about the same rate as other dog breeds. Which of the following would be a logical explanation for her failure?

B) The tendency to bark is not a heritable trait

Which of the following statements regarding natural selection is false?

C) Natural selection starts with the creation of new alleles that are directed toward improving an organism’s fitness.

Which of the following disciplines has found evidence for evolution based on the native distributions (locations) of living species?

Which of the following represents a pair of homologous structures?

B) the wing of a bat and the flipper of a whale

A) a group of individuals of the same species living in the same place at the same time.

Microevolution, or evolution at its smallest scale, occurs when

E) a population’s allele frequencies change over a span of generations.

The ultimate source of all new alleles is

A) mutation in parent cells (asexual organisms) or in cells that produce gametes (sexual organisms).

Imagine that you are studying a very large population of moths that is isolated from gene flow. A single gene controls wing color. Half of the moths have white-spotted wings (genotype WW or Ww) and half of the moths have plain brown wings (ww). There are no new mutations, individuals mate randomly, and there is no natural selection on wing color. How will p, the frequency of the dominant allele, change over time?

B) p will neither increase nor decrease it will remain more or less constant under the conditions described.

Genetic drift resulting from a disaster that drastically reduces population size is called

Thirty people are selected for a long-term mission to colonize a planet many light years away from Earth. The mission is successful and the population rapidly grows to several hundred individuals. However, certain genetic diseases are unusually common in this group, and their gene pool is quite different from that of the Earth population they have left behind. Which of the following phenomena has left its mark on this population?

Genetic differences between populations tend to be reduced by

Which of the following will tend to produce adaptive changes in populations?

A rabbit population consists of animals that are either very dark on top or very light on top. The color pattern is not related to sex. No rabbit shows intermediate coloration (medium darkness). This pattern might result from

Mate-attracting features such as the bright plumage of a male peacock result from

A woman struggling with a bacterial illness is prescribed a month’s supply of a potent antibiotic. She takes the antibiotic for about two weeks and feels much better. Should she save the remaining two-week supply, or should she continue taking the drug?

e. She should continue taking the drug until her immune system can completely eliminate the infection. Otherwise the remaining bacteria in her system may recover, and they will probably be resistant.

Which of the following would a biologist describe as microevolution?

E) a change in allele frequencies within the gene pool of a population

A biological species is defined as a group of organisms that

E) have the potential to interbreed in nature and produce fertile offspring.

The biological species concept is

D) difficult to put into practice even for present sexual organisms, and useless for asexual organisms and fossils.

Which provides the most general and correct description of the idea of a reproductive barrier?

B) a biological difference between two species that prevents them from successfully interbreeding

Which of the following types of reproductive barriers separates two species of sea cucumbers, whose sperm and eggs often bump into each other but do not cross-fertilize because of incompatible proteins on their surfaces?

Which of the following types of reproductive barriers separates a pair of species that could interbreed except that one mates at dusk and the other at dawn?

Which of the following types of reproductive barriers separates two flowering plant species that could interbreed except that one has a deep flower tube and is pollinated by bumblebees, whereas the other has a short, narrow flower tube and is pollinated by honeybees?

Which of the following types of reproductive barriers separates a pair of moth species that could interbreed except that the females’ mating pheromones are not attractive to the males of the other species?

Which of the following types of reproductive barriers separates a pair of insect species that could interbreed except that one mates on goldenrod flowers and the other on autumn daisies that both blossom at the same time?

Two species that sometimes mate and produce vigorous but sterile offspring are separated by

C) reduced hybrid fertility

The likelihood of allopatric speciation increases when a splinter population is ________ and ________ the broader range of the species.

Speciation without geographic isolation is called ________ speciation.

Organisms that possess more than two complete sets of chromosomes are said to be

Sympatric speciation commonly occurs through ________ in plants, but is more likely to occur through ________ in animals.

A) polyploidy . . . habitat differentiation and sexual selection

In a hybrid zone, ________ can occur if the reproductive barrier between two species is weak, as seen among cichlids in the murky waters of modern Lake Victoria.

A carrier of a genetic disorder who does not show symptoms is most likely to be __________ to transmit it to offspring.

heterozygous for the trait and able

a breeding experiment in which the parental varieties differ in only one trait.

A population of 1,000 birds exists on a small Pacific island. Some of the birds are yellow, a characteristic determined by a recessive allele. The others are green, a characteristic determined by a dominant allele. A hurricane on the island kills most of the birds from this population. Only ten remain, and those birds all have yellow feathers. Which of the following statements is true?

The hurricane has caused a population bottleneck.

A rabbit population consists of animals that are either very dark on top or very light on top. When examining them closely, biologists were surprised to find no rabbit with a medium darkness, intermediate to the two extremes. This is an example of

Alleles of a gene are found at __________ chromosomes.

the same locus on homologous

Amniocentesis and chorionic villus sampling allow for __________ and __________ of the fetus so that it can be tested for abnormalities.

karyotyping . . . biochemical testing

An elk herd is observed over many generations. Most of the full-grown bull elk have antlers of nearly the same size, although a few have antlers that are significantly larger or smaller than this average size. The average antler size remains constant over the generations. Which of the following effects probably accounts for this situation?

Any gene located on a sex chromosome

is called a sex-linked gene.

Assuming that the probability of having a female child is 50% and the probability of having a male child is also 50%, what is the probability that a couple’s first-born child is female and second-born child is male?

Certain whale species were hunted to near extinction. With a moratorium on hunting them, their population sizes have expanded. Which of the following is true?

The populations may still be endangered because they may have little remaining genetic variation.

Dr. Smith’s parents have normal hearing. However, Dr. Smith has an inherited form of deafness. Deafness is a recessive trait that is associated with the abnormal allele d. The normal allele at this locus, associated with normal hearing, is D. Dr. Smith’s parents could have which of the following genotypes?

Given the sex determination system in bees, we can expect that

female bees produce eggs by meiosis, while male bees produce sperm by mitosis

Large antlers in male elk, which are used for battles between males, are a good example of

Many genetic disorders of humans are caused by

Mendel’s law of independent assortment states that

each pair of alleles segregates independently of the other pairs of alleles during gamete formation.

Natural selection and the ability to generate perfection are limited by all of the following except that

organisms with the greatest fitness often don’t reproduce.

Research since Mendel’s time has established that the law of the segregation of genes during gamete formation

applies to all sexually reproducing organisms.

Tay-Sachs is inherited as an autosomal recessive allele. Homozygous individuals die within the first few years of life. However, there is some evidence that heterozygous individuals are more resistant to tuberculosis. Which of the following statements is true?

This situation is an example of heterozygote advantage.

The degree of adaptation that can occur in a population is limited by

the amount and kind of genetic variation in a population.

The fossil record shows all of following except that

the first life forms were eukaryotes.

The genetic variation among individuals in a sexually reproducing population of a plant that does not self-pollinate is the result of

A) gene mutation. B) crossing over during meiosis. C) independent assortment of chromosomes during meiosis. D) random fertilization.

The modern evolutionary synthesis

A) was first formed in the 1940s. B) focuses on populations as the units of evolution. C) includes the central role of natural selection. D) incorporates population genetics and ideas from paleontology, taxonomy, and biogeography

The vast majority of people afflicted with recessive disorders are born to parents who were

not affected at all by the disease.

Varieties of plants in which self-fertilization produces offspring that are identical to the parents are referred to as

What is meant by the statement that "male bees are fatherless"?

Male bees develop from unfertilized eggs.

Which of the following best explains why dominant alleles that cause lethal disorders are less common than recessive alleles that cause lethal disorders?

Most individuals carrying a lethal dominant allele have the disorder and die before they reproduce, whereas individuals carrying a lethal recessive allele are more likely to be healthy and reproduce.

Which of the following conditions would tend to make the Hardy-Weinberg equation more accurate for predicting the gene frequencies of future generations in a population of a sexually reproducing species?

little gene flow with surrounding populations

Which of the following is/are recessive sex-linked human conditions?

A) red-green color blindness B) muscular dystrophy C) hemophilia

Which of the following promote(s) genetic variation in a population?

A) heterozygote advantage B) frequency-dependent selection C) balancing selection

Which of the following provides evidence that vertebrates evolved from a common ancestor?

A) homologous structures B) the common development of pharyngeal pouches in an embryonic stage C) the presence of similar genes D) similarities in protein structure

Which one of the following is an example of incomplete dominance in humans?

Darwin found that some of the species on the Galapagos islands resembled species of the South American mainland

More than they resembled animals on ecologically similar but distant islands

Which of the following statements would Darwin have disagreed with?

Descent with modification occurs through inheritance of acquired characteristics

Lyell’s book Principles of Geology, which Darwin read on board the H.M.S Beagle, argued in favor of which of the following concepts?

Earth’s surface is shaped by natural forces that act gradually and are still acting

Which of the following assumptions or observations contradicts Darwin’s idea of natural selection?

Whether an organism survives and reproduces is almost entirely a matter of random chance

Which of the following statements regarding the currently available fossil record is false?

It is fully decomposed by bacteria and fungi

Which of the following statements regarding the currently available fossil record is false?

The currently available fossil record shows that the first life forms were eukaryotes

Humans share several features with salamanders. Certain genes and proteins are nearly identical between the two species both species have four limbs with a similar skeletal structure the species’ early embryos are very similar and where the salamander has a functional tail, humans have a vestigial tailbone. In evolutionary terms, these are examples of

Deep branch points near the base, or truck, of an evolutionary tree represent ______, while branch points near the tips of the branches represent ______

Relatively ancient common ancestors…relatively recent common ancestors

Which sentence best describes the true nature of natural selection?

Heritable traits that promote reproduction become more frequent in a population from one generation to the next

Which of the following would most quickly be eliminated by natural selection?

A harmful allele in an asexual, haploid population

Describe the adaptations of the blue-footed boobie

big webbed feet, streamlined shape, large tail, and specialized salt secreting glands

Describe the main ideas that Darwin advanced in his works

species change over time b. living species have arisen from earlier life forms

Describe the assumptions that were part of Darwin ‘s theory of natural selection.

1. individuals whose inherited traits give them a higher probability of surviving and reproduceing in a given environment tend to leave more offspring than other individuals. 2. this unequal production of offspring will cause favorable traits to accumulate in a population over time

The first life forms were prokaryotic or eukaryotic

How do fossils provide support for evolution?

Fossils show that life forms have changed over time, and radioactive dating shows the times at which the earlier forms lived

List the different types of evidence that modern species have evolved from prior species

a. molecular biology b. comparative anatomy c. comparative embryology d. biogeography

Be able to identify homologous structures (like the examples in your text)

arms, forelegs, flippers, and wings

What factors promote genetic variation in a population

migration of new individuals into the population mutation of alleles in the population genetic drift in the population due to random events

In a particular environment, there are no obvious fitness differences among individuals with dark hair and individuals with light hair. The term that best describes this situation is

Fitness increases when an organism

passes on a greater proportion of it’s genes to the next generation

Organisms that possess more than two complete sets of chromosomes are said to be
A) haploid
B) polyploid
C) diploid
D) hybrids

Under the biological species concept, a species is a group of organisms that
A) are physically similar
B) share a recent common ancestor
C) have the potential to interbreed in nature and produce fertile offspring
D) live together in a location and carry out identical ecological roles

C) have the potential to interbreed in nature and produce fertile offspring

Which branch of biology is concerned with the naming and classifying of organisms?
a. informatics
b. schematic biology
c. taxonomy
d. genomics

Mutations by themselves are rarely the cause of evolution in populations of plants and animals because:

Large antlers in male elk, which are used for battles between males, are a good example of

Genetic differences between populations tend to be reduced by

Mate-attracting features such as the bright plumage of a male peacock result from

A change in the relative frequencies of alleles in the gene pool of a population is called

A random change in an organism’s DNA

Certain whale species were hunted to near extinction. With a moratorium on hunting them, their population sizes have expanded. Which of the following is true?

The populations may still be endangered because they may have little remaining genetic variation

What is the result of natural selection?

a change in the gene pool of a population due to differential reproductive success

Which of the following provides evidence that vertebrates evolved from a common ancestor?

All of the choices are correct: similarities in protein structure, common development of pharyngeal pouches, homologous structures, the presence of similar genes

Which one of the following is false? Natural selection

Results from an organism’s needs

Which one of the following is false?

All variation in a population is heritable

Natural selection is often described as "survival of the fittest" The best measure of an organism’s fitness is

How many offspring it produces

Which of the following promote(s) genetic variation in a population?

All of the choices promote genetic variation in a population: balancing selection, heterozygote advantage, frequency-dependent selection

Analogous structures found in two species are structures that have

Similar overall shape due to common function

Which one of the following was not a main idea that Darwin advanced in his works?

New species can form by inheritance of acquired characteristics

The term macroevolution refers to which one of the following

Grand scale of evolution over many geological time

The unifying theme of biology is

Tay-Sachs is inherited as an autosomal recessive allele. Homozygous individuals die within the first few years of life. However, there is some evidence that heterozygous individuals are more resistant to tuberculosis. Which of the following statements is true?

This situation is an example of heterozygote advantage

Which one of the following represents two structures that are homologous?

The wing of a bat and the flipper of a whale

Long-legged cheetahs are well adapted to catching prey. The ancestor of the cheetah is believed to have had relatively short legs. According to Darwinian views, the evolution of long-legged cheetahs is best explained by

A plant breeder has been trying to develop a strain of snap dragons with blue flowers from a population of snapdragons some of which have white flowers and some of which have blue flowers. He finds that no matter how careful he is to only select blue flowered snap dragons, when he plants them out side roughly 10% of the snapdragons have white flower and some plants have both blue and white flowers on the same plant. The most likely explanation is:

Selection can only act on heritable variation and the white flower is due to environment

Mutations by themselves are rarely the cause of evolution in populations of plants and animals because:

Which of the following assumptions was not part of Darwin’s theory of natural selection?

Traits are inherited as discrete particles

Fitness increases when an organism

passes on a greater proportion of its genes to the next generation

The disease phenylketonuria (PKU. is caused by a recessive allele, and one child in 10,000 is born with the disease. Let q represent the frequency of the PKU allele. What is the value of q2? (Fetuses with PKU are no likelier than other fetuses to die before birth..

A population of 1,000 birds exists on a small Pacific island. Some of the birds are yellow, a characteristic determined by a recessive allele. The others are green, a characteristic determined by a dominant allele. A hurricane on the island kills most of the birds from this population. Only ten remain, and those birds all have yellow feathers. Which of the following statements is true?

The hurricane has caused a population bottleneck

What term is used to refer to structures that have a similar origin or ancestry even though they may be very different in appearance?

In a cell in which 2n = 6, the independent assortment of chromosomes during meiosis can by itself give rise to __________ genetically different gametes

the smallest unit that can evolve

The core theme of biology is

Species are fixed (permanent) and perfect

More than they resembled animals on ecologically similar but distant islands

Darwin found that some of the species on the Galapagos islands resembled species of the South American mainland

Descent with modification occurs through inheritance of acquired characteristics

Which of the following statements would Darwin have disagreed with?

Earth’s surface is shaped by natural forces that act gradually and are still acting

Lyell’s book Principles of Geology, which Darwin read on board the H.M.S Beagle, argued in favor of which of the following concepts?

The tendency to bark is not a heritable trait

A dog breeder wishes to develop a breed that does not bark. She starts with a diverse mixture of dogs. Generation after generation, she allows only the quietest dogs to breed. After 30 years of work she has a new breed of dog with interesting traits, but on average, the dogs still bark at about the same rate as other dog breeds. Which of the following would be a logical explanation for her failure?

Whether an organism survives and reproduces is almost entirely a matter of random chance

Which of the following assumptions or observations contradicts Darwin’s idea of natural selection?

Differential reproductive success based on inherited characteristics

Which of the following best expresses the concept of natural selection?

Who developed a theory of evolution almost identical to Darwin’s?

Natural selection starts with the creation of new alleles that are directed toward improving an organism’s fitness

Which of the following statements regarding natural selection is false?

It is fully decomposed by bacteria and fungi

Which of the following statements regarding the currently available fossil record is false?

The currently available fossil record shows that the first life forms were eukaryotes

Which of the following statements regarding the currently available fossil record is false?

Which of the following disciplines has found evidence for evolution based on the native distributions (locations) of living species?

Humans share several features with salamanders. Certain genes and proteins are nearly identical between the two species both species have four limbs with a similar skeletal structure the species’ early embryos are very similar and where the salamander has a functional tail, humans have a vestigial tailbone. In evolutionary terms, these are examples of

Relatively ancient common ancestors…relatively recent common ancestors

Deep branch points near the base, or truck, of an evolutionary tree represent ______, while branch points near the tips of the branches represent ______

A change in allele frequencies within the gene pool of a population

Which of the following would a biologist describe as microevolution?

Have the potential to interbreed in nature and produce fertile offspring

A biological species is defined as a group of organisms that

Organisms that possess more than two complete sets of chromosomes are said to be

10 to 20 billion years ago

The "big bang" that produced the universe is though to have occurred

The earliest discovered fossils are of ______ dating back to ______ years ago.

The atmosphere was rich in gases released in volcanic eruptions volcanic activity, lightning, and ultraviolet radiation were all much more intense than on today’s Earth

When the Earth first solidified, what were conditions like?

A group of individuals of the same species living in the same place at the same time

A population’s allele frequencies change over a span of generations

Microevolution, or evolution at its smallest scale, occurs when

Mutation in parent cells (asexual organisms) or in cells that produce gametes (sexual organisms)

The ultimate source of all new alleles is

Heritable traits that promote reproduction become more frequent in a population from one generation to the next

Which sentence best describes the true nature of natural selection?

She should continue taking the drug until her immune system can completely eliminate the infection. Otherwise the remaining bacteria in her system may recover, and they will probably be resistant

A woman struggling with a bacterial illness is prescribed a month’s supply of a potent antibiotic. She takes the antibiotic for about two weeks and feels much better. Should she save the remaining two-week supply, or should she continue taking the drug?

A harmful allele in an asexual, haploid population

Which of the following would most quickly be eliminated by natural selection?

A northern landmass called Laurasia and a southern landmass called Gondwana

When the continent of Pangaea first split apart, it formed

Classify species in groups that reflect evolutionary relationships

Ever since Darwin, systematics has tried to

Only within the domain Eukarya

In the three-domain system, the eukaryotes are represented

Subdivides the prokaryotes into two different domains

Organisms have evolved over time…beginning with the formation of molecules…then the molecules formed organisms…and those organisms formed more complex organisms

There are numerous theories of evolution with the common thought

God is the creator of all

There are numerous theories of creation with the common thought

There is a higher, intelligent being that made all that we see today (Irreducible Complexity)

Another way of explaining our origin is intelligent design with the common thought

Mutations by themselves are rarely the cause of evolution in populations of plants and animals because:

Large antlers in male elk, which are used for battles between males, are a good example of

Genetic differences between populations tend to be reduced by

Mate-attracting features such as the bright plumage of a male peacock result from

A change in the relative frequencies of alleles in the gene pool of a population is called

A random change in an organism’s DNA

Certain whale species were hunted to near extinction. With a moratorium on hunting them, their population sizes have expanded. Which of the following is true?

The populations may still be endangered because they may have little remaining genetic variation

What is the result of natural selection?

a change in the gene pool of a population due to differential reproductive success

Which of the following provides evidence that vertebrates evolved from a common ancestor?

All of the choices are correct: similarities in protein structure, common development of pharyngeal pouches, homologous structures, the presence of similar genes

Which one of the following is false? Natural selection

Results from an organism’s needs

Which one of the following is false?

All variation in a population is heritable

Natural selection is often described as "survival of the fittest" The best measure of an organism’s fitness is

How many offspring it produces

Which of the following promote(s) genetic variation in a population?

All of the choices promote genetic variation in a population: balancing selection, heterozygote advantage, frequency-dependent selection

Analogous structures found in two species are structures that have

Similar overall shape due to common function

Which one of the following was not a main idea that Darwin advanced in his works?

New species can form by inheritance of acquired characteristics

The term macroevolution refers to which one of the following

Grand scale of evolution over many geological time

The unifying theme of biology is

Tay-Sachs is inherited as an autosomal recessive allele. Homozygous individuals die within the first few years of life. However, there is some evidence that heterozygous individuals are more resistant to tuberculosis. Which of the following statements is true?

This situation is an example of heterozygote advantage

Which one of the following represents two structures that are homologous?

The wing of a bat and the flipper of a whale

Long-legged cheetahs are well adapted to catching prey. The ancestor of the cheetah is believed to have had relatively short legs. According to Darwinian views, the evolution of long-legged cheetahs is best explained by

A plant breeder has been trying to develop a strain of snap dragons with blue flowers from a population of snapdragons some of which have white flowers and some of which have blue flowers. He finds that no matter how careful he is to only select blue flowered snap dragons, when he plants them out side roughly 10% of the snapdragons have white flower and some plants have both blue and white flowers on the same plant. The most likely explanation is:

Selection can only act on heritable variation and the white flower is due to environment

Mutations by themselves are rarely the cause of evolution in populations of plants and animals because:

Which of the following assumptions was not part of Darwin’s theory of natural selection?

Traits are inherited as discrete particles

Fitness increases when an organism

passes on a greater proportion of its genes to the next generation

The disease phenylketonuria (PKU. is caused by a recessive allele, and one child in 10,000 is born with the disease. Let q represent the frequency of the PKU allele. What is the value of q2? (Fetuses with PKU are no likelier than other fetuses to die before birth..

A population of 1,000 birds exists on a small Pacific island. Some of the birds are yellow, a characteristic determined by a recessive allele. The others are green, a characteristic determined by a dominant allele. A hurricane on the island kills most of the birds from this population. Only ten remain, and those birds all have yellow feathers. Which of the following statements is true?

The hurricane has caused a population bottleneck

What term is used to refer to structures that have a similar origin or ancestry even though they may be very different in appearance?

In a cell in which 2n = 6, the independent assortment of chromosomes during meiosis can by itself give rise to __________ genetically different gametes

the smallest unit that can evolve

1) The term "gene expression" refers to the

D) process by which genetic information flows from genes to proteins.

2) A gene operon consists of

D) transcribed genes, an operator, and a promoter.

3) In a prokaryote, a group of genes with related functions, along with their associated control sequences, defines

4) The lac operon in E. coli

C) prevents lactose-utilizing enzymes from being expressed when lactose is absent from the environment.

5) Proteins that bind to DNA and turn on operons by making it easier for RNA polymerase to bind to a promoter are called

6) The lac operon of E. coli is ________ when the repressor is bound to lactose.

7) The expression of the tryptophan operon is controlled by

D) a repressor that is active when it binds to tryptophan.

8) Which of the following is likely to occur in E. coli cells that are grown in skim milk?

D) The trp repressor is activated and the cells will produce lactose-utilizing enzymes.

9) A single cell, the zygote, can develop into an entirely new organism with many different specialized cells. Which of the following statements about this process is false?

B) Additional genetic information for the formation of specialized cells is passed on to the developing embryo via the placenta.

10) The basis of cellular differentiation is

A) selective gene expression.

11) The genes for the enzymes of glycolysis

A) are active in all metabolizing cells, but the genes for specialized proteins are expressed only in particular cell types.

12) Which of the following statements regarding DNA packing is false?

C) DNA packing tends to promote gene expression.

13) The relationship between DNA and chromosomes is most like

B) thread wrapped around a spool.

14) In female mammals, the inactive X chromosome in each cell

15) The tortoiseshell pattern on a cat

B) results from X chromosome inactivation.

16) Both prokaryotic and eukaryotic cells use ________ to turn certain genes on or off.

A) DNA sequences to which activator proteins bind.

C) bind to DNA sequences and inhibit the start of transcription.

19) RNA splicing involves the

A) removal of introns from the molecule.

20) The coding regions of a gene (the portions that are expressed as polypeptide sequences) are called

21) Which of the following permits a single gene to code for more than one polypeptide?

C) alternative RNA splicing

22) Small pieces of RNA that can regulate translation of mRNA are called

B) cells to prevent infections from double-stranded RNA viruses.

24) All of the following mechanisms are used to regulate protein production except

25) Which of the following mechanisms of controlling gene expression occurs outside of the nucleus?

26) Which of the following statements about fruit fly development is false?

D) The location of the head and tail ends of the egg is primarily determined by the location of sperm entry during fertilization.

A) serves as a master control gene that functions during embryonic development by controlling the developmental fate of groups of cells.

28) Which of the following statements about microarrays is false?

A) Microarrays use tiny portions of double-stranded RNA fragments from a large number of genes.

29) In multicellular organisms, the coordination of cellular activities relies on

A) cell-to-cell signaling and signal transduction pathways.

30) To initiate a signal transduction pathway, a signal binds to a receptor protein usually located in the

31) Transcription factors attach to

32) A signal outside a cell triggers changes in the transcription and translation inside the cell through

B) signal transduction pathways.

33) Yeast are able to communicate with each other

B) through chemical signaling.

34) Signal transduction pathways

A) are mechanisms of communication that probably evolved in ancient prokaryotes.

35) In plants, most differentiated cells retain

C) a complete set of their genes, and retain the ability to express those genes under certain circumstances.

36) Why can some plants be cloned from a single cell?

D) Plant cells can dedifferentiate and give rise to all of the specialized cells required to produce an entire plant.

37) Which of the following processes occurs when a salamander regenerates a lost limb?

A) Certain cells in the limb dedifferentiate, divide, and then redifferentiate to form a new limb.

38) The cloning of Dolly the sheep

D) demonstrated that the nuclei from differentiated mammalian cells can retain their full genetic potential.

39) The use of cloning to produce special embryonic stem cells is called

40) Which of the following mammals has not yet been cloned and brought through the complete gestation cycle?

41) Which of the following possible uses of reproductive cloning is still considered by most to be an unresolved ethical issue?

A) the reproductive cloning of humans

42) Which of the following statements regarding stem cells is false?

B) Adult, but not embryonic, stem cells can be grown in laboratory culture.

43) Adult stem cells have limited therapeutic potential

B) because their developmental potential is limited to certain tissues.

44) A gene that can cause cancer when present in a single copy in a cell is called a(n)

45) Which of the following statements about proto-oncogenes is false?

B) A mutation in a tumor-suppressor gene can stop cell division immediately.

46) Which of the following is not a factor that contributes to normal cells becoming cancerous?

D) one or more of the cell’s genes being removed by a virus

47) Cancer of the colon is caused by

D) several somatic cell mutations.

48) The development of colon cancer occurs slowly, and colon cancer is more frequently seen in the elderly than the young. This is most likely because

C) four or more somatic mutations must occur to give rise to the cancer, which takes time.

49) Mutations in the proto-oncogene ras and the tumor suppressor gene p53

B) disrupt normal regulation of the cell cycle.

50) Mutations in the p53 gene can lead to cancer by

A) causing the production of a faulty protein that is no longer able to inhibit cell division.

51) The carcinogen known to cause the most cases and types of cancer is

52) Which of the following statements regarding cancer risk factors is false?

D) Mutagens are usually not carcinogens.

53) In this drawing of the lac operon, which molecule is an inactive repressor?

54) Which structure in this figure shows one complete nucleosome?

55) Why don’t the grafted hybrids produce apples with a blend of traits from the scion and the rootstock?

D) The rootstock regulates gene expression in the scion, but contributes no genetic information for fruit production.

56) Half the trees in an orchard were derived from rootstock "A" and half from rootstock "B," but all the
trees had the same scion. If the trees grafted onto rootstock "A" were infected by a parasite that
causes blossom rot, the trees grafted onto rootstock B

A) would be very likely to become infected, because the remaining scions are genetically identical to those that are already infected.

Cells to prevent infections from double-stranded RNA viruses.

The type of recombinant bacteria most often used to mass-produce genes is

When DNA from two sources is combined into one single piece of DNA, it is known as

Approximately what percentage of the human genome is identical to that of a chimpanzee?

The feature of "sticky ends" that makes them especially useful in DNA recombination is their ability to

form hydrogen-bonded base pairs with complementary single-stranded stretches of DNA

What is the preferred name of the technique used to determine if DNA comes from a particular individual?

Approximately what percentage of human DNA is noncoding?

has been around since the dawn of civilization

In the process of human gene cloning using recombinant plasmids, the bacterial plasmid

During the process of electrophoresis, the _______ functions like a thick filter, separating the samples according to their size.

cut DNA at specific sites

When DNA fingerprinting was first used,

the two semen samples did not match the person who initially confessed

Restriction enzymes specifically recognize and cut short sequences of DNA called

The production of multiple identical copies of gene-sized pieces of DNA defines

Which of the following statements regarding DNA is false?

Scientists think that the typical human gene probably specifies just one polypeptide.

A collection of DNA fragments obtained from the genome of one organism, inserted by recombinant DNA techniques into the genome of a host organism (one fragment per host genome), and maintained there is called a

Which step in this process requires use of restriction enzymes?

In order to match the pilot’s remains to the correct family using DNA profiling,

each of the 13 STR bands must match

Based on analysis of the STR sites shown, does the missing pilot belong to any of these three families?

Gel electrophoresis sorts DNA molecules on the basis of their

In order for gene therapy to be permanent,

the normal gene must be transferred to somatic cells that can continuously multiply

If you commit a crime, you need to make sure that you do not leave even the smallest speck of blood, hair or other organic matter from your body. If you do, the DNA in this material can be amplified by ______, subjected to genetic analysis, and used to identify you as the perpetrator of the crime.

a piece of radioactively labeled DNA that is used to locate a specific gene.

_________ are a major source of restriction enzymes.

DNA fragments that have matching sticky ends are joined by covalent bonds formed by the action of

When plasmids are used to produce a desired protein,

the desired gene is inserted into the plasmid and the plasmid is returned to the bacterium by transformation.

The advantage of being able to clone the gene for human insulin is that

human insulin is less likely to provoke an allergic reaction than cow, pig or horse insulin.

stimulating the immune system.

Which of the following pieces of evidence would be considered the best for establishing biological relatedness?

a very close match in the DNA profile

The number of proteins in humans

is much greater than the number of genes

Decisions regarding the human genome are the responsibility of

society as a whole (individuals, doctors, scientists, government)

The electrical current in the electrophoresis chamber always runs

Remove the bacterial plasmid/cut using a restriction enzyme

Harvest/purify the insulin protein to be injected into patients

Put the bacterial plasmid back into the bacterial cell where it can reproduce and synthesize the insulin protein

Isolate in insulin gene in human DNA using the same restriction enzyme

Insert the insulin gene into the bacterial plasmid/Seal with ligase

Separate the fragments using electrophoresis

Cut the DNA using a restriction enzyme

Analyze/Interpret the results

Why is the whole-genome shotgun method currently the tool of choice for analyzing genomes?

It is fast and inexpensive

which of the following genetically modified organisms has not been developed by genetic engineers

Transgenic corn with the gene for human insulin

Which of the following has NOT been a significant issue in the creation of genetically modified organisms?

The fact that GM organisms cannot be modified to prevent them from reproducing once they pass beyond the experimental stage.

golden rice is golden in color because it is rich in

which of the following statements regarding proteomics is correct?

Proteomics is the systemic study of the full set of proteins encoded by a genome.

the only recombinant cells that can correctly attach sugars on proteins to form glycoprotein products are

which of the following statements about dna technology is false

DNA technology is now used to create cells that can identify and kill cancer cells

genomic libraries can be constructed using either bacterial plasmids or what other vector

An animal containing a gene from another organism, typically of another species.

which of the following statements regarding repetitive dna is false?

Repetitive DNA is identical in all humans

after dna fragments with matching sticky ends are temporarily joined by complementary base-pairing, the union can be made permanent by the "pasting" enzyme

genome sequence analysis suggest that neanderthals

Atleast sometimes had pale skin and red hair

Segments of eukaryotic DNA that can move or be copied from one site to another in the genome are called

The ________ approach to gene cloning employs a mixture of fragments from the entire genome of an organism.

Blue-footed boobies have webbed feet and are comically clumsy when they walk on land. Evolutionary scientists view these feet as

the outcome of a tradeoff: webbed feet perform poorly on land, but are very helpful in diving for food.

Which of the following statements would Darwin have disagreed with?

Descent with modification occurs through inheritance of acquired characteristics

Broccoli, cabbages, and Brussels sprouts all descend from the same wild mustard and can still interbreed. These varieties were produced by.

Humans share several features with salamanders. Certain genes and proteins are nearly identical between the two species: both species have four limbs with a similar skeletal structure the species vestigial tailbone. In evolutionary terms, these are examples of

Darwin was the first person to draw an evolutionary tree, a diagram that represents

evidence- based hypotheses regarding our understanding of patterns of evolutionary descent.

Which sentence best describes the true nature of natural selection?

Heritable traits that promote reproduction become more frequent in a population from one generation to the next.

An elk herd is observed over many generations. Most of the full-grown bull elk have antlers of nearly the same size. The average antler size remains constant over the generations. Which of the following effects probably accounts for the situation?

A women struggling with bacterial illness is prescribed a months supply of a potent antibiotic. She takes the antibiotic for about 2 weeks and feels much better. Should she save the remaining two week supply or should she continue taking the drug?

She should continue taking the drug until her immune system can completely eliminate the infection. Otherwise the remaining bacteria in her system may recover, and they will probably be resistant

The sickle-cell allele produces a serious blood disease in homozygotes. Why doesn’t natural selection eliminate this allele from all human populations?

In populations were endemic malaria is present, heterozygotes have an important advantage: They are resistant to malaria and therefore are more likely to survive and produce offspring that carry the allele.

Frequency-dependent selection, as seen in the case of the scale-eating fish in lake Tanganyika, tends to

maintain two phenotypes in a dynamic equilibrium in a population

During which of the following stages of food processing is undigested material removed from the digestive tract

An alimentary canal is best defined as

a tube-shaped compartment for the transport, digestion, and absorption of food

Which of the following correctly lists the order of the parts of the human digestive system, from first to last contact with food matter?

oral cavity, pharynx, esophagus, stomach, small intestine, large intestine

The mucous-producing cells that line the stomach

lubricate and protect the stomach lining

In the digestive system, most nutrient absorption occurs in the

organisms suffering from malnutrition may have a diet deficient in

one or more essential nutrients

which of the following is a hormone produced by adipose cells that help to control appetite?

Animals that maintain internal body temperature using heat generated by their own metabolism are called

To enhance heat loss, humans sweat, an adaption known as

sweating commonly results in dehydration. Of the choices listed, which would be the best option for rehydration after intense exercise?

mammals have evolved a sophisticated mechanism for eliminating nitrogenous wastes that involves

forming urea and storing it in concentrated solution

whats is the name of the functional unit of the kidneys

during production of urine, a major function of the kidney is

what is the function of antidiurectic hormone?

to increase water reabsorption

when a salmon moves from the ocean to a freshwater environment, you would expect its urine volume to _______ and its rate of salt absorption to ______.

In a dialysis machine, wastes are removed from blood plasma by process of

through which of the following structures does urine leave the bladder?

increased brain size had many benefits for early humans. one example is

complex social structure with the ability to adapt to changing environments

when comparing the differences between human and chimpanzee DNA

the differences are generally found in the gene switches that determine when and how genes are expressed.

walking upright has both pros and cons. some of the pros of walking upright include

looking large to predators, the ability to harvest more food, the ability to carry young.

homo erectus was the first early human to spend most of its time walking upright

tool use is uniquely human

chimpanzees are humans closest living relatives

lower back pain can be attributed to walking upright, which formed the curvature at the base of the spine

Humans and chimpanzees have 90% identical genome sequences

Darwins ideas about evolution were formed after observing marine iguanas on the galapagos islands

____ genes are responsible for coding for self-proteins.

A molecule that can elicit an adaptive immune response is called

Medullary breathing centers directly sense and respond to

blood pH and CO2 concentration

which part of the diagram shows the alveoli?

Air leaving human lung during exhalation contains

carbon dioxide and unused oxygen

during gas exchange, body cells

release CO2 and take in O2

As blood moves away from the heart towards the tissues, the relative size of blood vessels _____, the blood pressure ______, and the velocity of blood flow _______.

which of the following is a function of the nasal cavities in humans?

arteries are distinguished from veins based on all of the following features except

the amount of oxygen present in the blood

The main function of the AV node is to

relay a signal for the ventricles to contract

The maximum amount of air that a human can inhale and exhale is called the

Which of the following cell types is responsible for the cell-mediated immune response?

attack virus-infected cells by releasing chemicals that lead to the death of the cell

Oxygen moves from blood into the interstitial fluid and then to body cells because

it diffuses from a region of higher partial pressure to a region of lower partial pressure

which of the following distingueshes the secondary immune response from the primary?

The secondary response is faster and stronger

which of the following choices best describes a plasma cell?

It is a differentiated B cell

Oxygen-poor blood is carried from the heart of a mammal to the lungs via the

What type of blood vessel is solely responsible for exchange between the blood and the interstitial fluid?

which of the following helps activate our nonspecific (innate) defense system?

A primary immune response is

the immune response elicited by the first exposure of lymphocytes to a particular antigen

cardiac output is defined as the volume of blood pumped by an ____ each time it contracts

Which of the following types of cells does HIV preferentially infect?

The reason animals need continuous supply of oxygen is

obtain energy from their food

after binding to an infected cell, the cytotoxic T cell

releases a protein called perforin

what part of the human brain contains the primary breathing control center?

multipotent stem cells found in the red marrow inside bones

can differentiate into all blood cells and platelets

An adult humans red blood cells are formed in the

which blood vessels have the thinnest walls

labored breathing, coughing, lung infections, and respiratory failure are characteristics defining

chronic obstructive pulmonary diseases

which of the following contributes to gas exchange in the human fetus

the stronger attraction that fetal hemoglobin has for oxygen when compared to adult hemoglobin

blood clots are formed by platelets and the plasma protein

which of the following statements about mammalian circulatory systems is false?

The left side of a mammals heart sends blood to the lungs

The liquid part of blood is called

what prompts a newborn baby to start to breather?

an increase in the concentration of oxygen in the baby’s blood

which of the following options correctly lists the direction of carbon dioxide travel as it leaves the body?

alveoli, bronchioles, bronchi, trachea, larynx, pharynx

which of the following is a function of the circulatory system?

transporting nutrients to body cells

The oxygen-carrying component in red blood cells is

which of the following wander through the interstitial fluid and consume any bacteria and virus-infected cells they encounter?

anaphylactic shock is an example of an

which of the following cells are phagocytes?

monocytes and neutrophils

which of the following can contribute to high blood pressure?

blood flow through capillaries is controlled by

precapillary sphincters and smooth muscle in the walls of arterioles

what type of immune response is always disadvantageous to a person?

which of the following cell types is responsible for the humoral immune response?

The human lymphatic system consists of all of the following structures except the

The basic function of the activated T cells is to battle

pathogens that have alreasy entered body cells

one kind of vaccine consists of

a harmless variant strain of a disease-causing microbe

cigarette smoke can affect the white blood cells that reside in our lungs, whose purpose is to

which of the following animals requires the largest and most complex lungs proportional to its overall body size?

Plasma proteins are involved in all of the following activities except

The autonomic nervous system

regulates the internal environment of the body

The central communication conduit between the brain and the rest of the body is the

functionally, the muscle fibers fundamental unit for contraction is the

muscles are connected to the bones by

a tennis player serving the ball uses fast muscle fibers. The ATP needed to accomplish this would come from

The signal that crosses a synapse is stopped when

the neurotransmitter is enzymatically broken down or transported back to the signaling cell

living cells that secrete a surrounding matrix

the neurotransmitter found at the synapse between nerves and human skeletal muscle cells is

which division of the human nervous system carries signals to skeletal muscles?

action potentials normally travel along an axon

According to the sliding filament model of muscle contraction, a sarcomere contracts when its

thin filaments slie towards each other across its thick filaments

work in antagonistic pairs

nervous system effector cells

include muscle cells and gland cells

which of the following statements regarding the brain is true

the blood-brain barrier helps to maintain a stable chemical environment for the brain

the gap between the transmitting and receiving neurons in a chemical synapse is known as the

The relationship between spinal nerves and the spinal cord is most like the relationship between

an interstate highway and the many roads that intersect with it via on- and off- ramps

which of the following structures constitutes part of the axial skeleton

The calcium that triggers muscle contraction is stored in

the endoplasmic reticulum

which of the following statements regarding exercise is true

the main source of energy during aerobic exercise is ATP from aerobic respiration

Osteoporosis is characterized by

low bone mass and structural deterioration of the bone tissue.

what part of the neuron carries signals toward the part of the cell that houses the nucleus

one neurotransmitter associated with sleep, mood, attention, and learning is

Muscles that are constantly active, such as those maintaining our body posture, having a high proportion of

slow, fatigue-resistant fibers.

Parkinsons disease is associated with a deficiency in

which of the following statements regarding the nervous system is true

motor neurons convey signals from the CNS to the effector cells

which of the following statements about resting potential is true

the sodium-potassium pump contributes to the resting membrane potential

changes occur within a sarcomere during muscle contraction. one change is that the

Z lines move closer together

The shoulder joint where the humerus meets the shoulder gridle is an example of

a motor neuron and all of the muscle fibers it controls

The speed of impulse conduction along an axon may be increase by

Neurotransmitters that open Na+ channels and trigger action potentials in receiving cells are called

The enteric division of the autonomic nervous system consists of neurons in the digestive tract, the gallbladder and

a thick filament consists of

which of the following statements about locomotion is true

locomotion requires animals to overcome friction and gravity

multiple sclerosis results from an autoimmune disease that primarily involves

destruction of the myelin sheath

which of the following statements best describes the power stroke of muscle contraction?

the myosin head bends, pulling the thin filament toward the center of the sarcomere

which part of a bone contains mostly stored fat?

during transmission across a typical chemical synapse

neurotransmitter molecules bind to receptors in the receiving cells plasma membrane

the functional unit of the nervous system is the

in all vertebrates, the brain consists of the

the sequence of events that cause a muscle to contract can be summed up in the correct order as

detach, extend, attach, pull

the contacting surfaces of a moving joint, such as your hip joint, consist of

action potentials relay different intensities of information due to the

frequency of action potentials relative to the strength of the stimulus

which of the following statements about skeletal muscle fibers is true

each muscle fiber contains actin and myosin

the two major anatomical divisions of the nervous system are the

central nervous system and peripheral nervous system

Which of the following statements regarding sexual reproduction is true?

Sexual reproduction generates greater genetic variation than asexual reproduction.

In which part of the human female reproductive system does fertilization normally take place?

Human testes are positioned in an external sac rather than in the abdominal cavity

so the testes can be kept cooler than the body’s interior.

Which of the following produces a thick fluid containing fructose, which is used for energy by sperm?

Which of the following statements comparing spermatogenesis and oogenesis is true?

Men, but not women, can produce gametes throughout their lives.

Which of the following STDs is caused by a virus that can also cause cancer?

Sterilization, in which the sperm is surgically prevented from reaching the egg, is accomplished by

tubal ligation or vasectomy.

The function of a sperm cell’s acrosome is to

carry enzymes that help the sperm penetrate the egg.

Which of the following serves as an impenetrable barrier that prevents more than one sperm from fertilizing an egg?

Which of the following occurs during the process of labor?

positive feedback involving oxytocin and prostaglandins

Mendel conducted his most memorable experiments on

An insect that has the genotype EeGGcc will have the same phenotype as an insect with the genotype _____.

In an individual of genotype Aa, where are the A and a alleles physically located?

One allele is on one chromosome, and the other is in the same position (locus) on the homologous chromosome.

The phenotypic ratio resulting from a dihybrid cross showing independent assortment is expected to be

Imagine that we mate two black Labrador dogs with normal vision and find that three of the puppies are like the parents, but one puppy is chocolate with normal vision and another is black with PRA (progressive retinal atrophy, a serious disease of vision). We can conclude that

the alleles for color and vision segregate independently during gamete formation.

Imagine that long fins in zebrafish is a dominant trait. A breeder wants to set up a breeding program beginning with homozygous dominant long-finned fish. If she obtains a handful of the long-finned fish, how can she tell which if any of these are homozygous for the trait?

Cross the long-finned fish with short-finned fish if the offspring are all long-finned, the long-finned parent is homozygous.

Dr. Smith’s parents have normal hearing. However, Dr. Smith has an inherited form of deafness. Deafness is a recessive trait that is associated with the abnormal allele d. The normal allele at this locus, associated with normal hearing, is D. Dr. Smith’s parents could have which of the following genotypes?

A carrier of a genetic disorder who does not show symptoms is most likely to be ________ to transmit it to offspring.

heterozygous for the trait and able

All the offspring of a cross between a red-flowered plant and a white-flowered plant have pink flowers. This means that the allele for red flowers is ________ to the allele for white flowers.

A woman has been trying to conceive for several years, unsuccessfully. At a fertility clinic, they discover that she has blocked fallopian tubes. Using modern technologies, some of her eggs are removed, fertilized with her husband’s sperm, and implanted into her uterus. The procedure is successful, but the couple discovers that their new son is color-blind and has blood type O. The woman claims that the child can’t be theirs since she has blood type A and her husband has type B. Also, neither parent is color-blind, although one grandparent (the woman’s father) is also color-blind.

As a genetic counselor, you would explain to the parents that

it is possible for the baby to have type O blood, since type O is inherited through a dominant allele.

has been around since the dawn of civilization.

After DNA fragments with matching sticky ends are temporarily joined by complementary base-pairing, the union can be made permanent by the "pasting" enzyme

The type of recombinant bacteria most often used to mass-produce genes is

The advantage of being able to clone the gene for human insulin is that

human insulin is less likely to cause harmful side effects than cow, pig, or horse insulin.

Which of the following has not been a significant issue in the creation of genetically modified (GM) organisms?

the fact that GM organisms cannot be modified to prevent them from reproducing once they pass beyond the experimental stage

What is the preferred name of the technique used to determine if DNA comes from a particular individual?

Gel electrophoresis sorts DNA molecules on the basis of their

What is the current standard tool used for DNA profiling by forensic scientists?

Which of the following statements about genomics is false?

DNA technology limits genomic studies to prokaryotes.

In "Cracking Your Genetic Code," what type of cancer was being targeted with drugs based on the genome of the cancer cells?

the type of repetitive dna composed of sequences of large repeated units is often associated with

A cDNA library differs from a genomic library in that

cDNA libraries only contain information from genes that have been transcribed.

when genetic variation in one nucleotide is found in at least 1 of the population it is known as

A. single nucleotide polymorphism.

Which of the following statements about nucleic acid probes is false?

A nucleic acid probe is a double-stranded section of DNA.

DNA fragments with single-stranded ends.

The polymerase chain reaction relies upon unusual, heat-resistant ________ that were isolated from bacteria living in hot springs.

Which of the following statements about genome sequencing is false?

Most of the genomes that have been sequenced to date are eukaryotes.

24. Genetically modifying ________ cells may directly affect future generations.

What is the smallest number of cells needed to perform a successful DNA profile?

An advantage of using reverse transcriptase to prepare a gene for cloning is that

the resulting DNA strand will lack introns.

The type of recombinant bacteria most often used to mass-produce genes is

When DNA from two sources is combined into one single piece of DNA, it is known as

Approximately what percentage of the human genome is identical to that of a chimpanzee?

The feature of "sticky ends" that makes them especially useful in DNA recombination is their ability to

form hydrogen-bonded base pairs with complementary single-stranded stretches of DNA

What is the preferred name of the technique used to determine if DNA comes from a particular individual?

Approximately what percentage of human DNA is noncoding?

has been around since the dawn of civilization

In the process of human gene cloning using recombinant plasmids, the bacterial plasmid

During the process of electrophoresis, the _______ functions like a thick filter, separating the samples according to their size.

cut DNA at specific sites

When DNA fingerprinting was first used,

the two semen samples did not match the person who initially confessed

Restriction enzymes specifically recognize and cut short sequences of DNA called

The production of multiple identical copies of gene-sized pieces of DNA defines

Which of the following statements regarding DNA is false?

Scientists think that the typical human gene probably specifies just one polypeptide.

A collection of DNA fragments obtained from the genome of one organism, inserted by recombinant DNA techniques into the genome of a host organism (one fragment per host genome), and maintained there is called a

Which step in this process requires use of restriction enzymes?

In order to match the pilot’s remains to the correct family using DNA profiling,

each of the 13 STR bands must match

Based on analysis of the STR sites shown, does the missing pilot belong to any of these three families?

Gel electrophoresis sorts DNA molecules on the basis of their

In order for gene therapy to be permanent,

the normal gene must be transferred to somatic cells that can continuously multiply

If you commit a crime, you need to make sure that you do not leave even the smallest speck of blood, hair or other organic matter from your body. If you do, the DNA in this material can be amplified by ______, subjected to genetic analysis, and used to identify you as the perpetrator of the crime.

a piece of radioactively labeled DNA that is used to locate a specific gene.

_________ are a major source of restriction enzymes.

DNA fragments that have matching sticky ends are joined by covalent bonds formed by the action of

When plasmids are used to produce a desired protein,

the desired gene is inserted into the plasmid and the plasmid is returned to the bacterium by transformation.

The advantage of being able to clone the gene for human insulin is that

human insulin is less likely to provoke an allergic reaction than cow, pig or horse insulin.

stimulating the immune system.

Which of the following pieces of evidence would be considered the best for establishing biological relatedness?

a very close match in the DNA profile

The number of proteins in humans

is much greater than the number of genes

Decisions regarding the human genome are the responsibility of

society as a whole (individuals, doctors, scientists, government)

The electrical current in the electrophoresis chamber always runs

Remove the bacterial plasmid/cut using a restriction enzyme

Harvest/purify the insulin protein to be injected into patients

Put the bacterial plasmid back into the bacterial cell where it can reproduce and synthesize the insulin protein

Isolate in insulin gene in human DNA using the same restriction enzyme

Insert the insulin gene into the bacterial plasmid/Seal with ligase

Separate the fragments using electrophoresis

Cut the DNA using a restriction enzyme

Analyze/Interpret the results

Why is the whole-genome shotgun method currently the tool of choice for analyzing genomes?

It is fast and inexpensive

which of the following genetically modified organisms has not been developed by genetic engineers

Transgenic corn with the gene for human insulin

Which of the following has NOT been a significant issue in the creation of genetically modified organisms?

The fact that GM organisms cannot be modified to prevent them from reproducing once they pass beyond the experimental stage.

golden rice is golden in color because it is rich in

which of the following statements regarding proteomics is correct?

Proteomics is the systemic study of the full set of proteins encoded by a genome.

the only recombinant cells that can correctly attach sugars on proteins to form glycoprotein products are

which of the following statements about dna technology is false

DNA technology is now used to create cells that can identify and kill cancer cells

genomic libraries can be constructed using either bacterial plasmids or what other vector

An animal containing a gene from another organism, typically of another species.

which of the following statements regarding repetitive dna is false?

Repetitive DNA is identical in all humans

after dna fragments with matching sticky ends are temporarily joined by complementary base-pairing, the union can be made permanent by the "pasting" enzyme

genome sequence analysis suggest that neanderthals

Atleast sometimes had pale skin and red hair

Segments of eukaryotic DNA that can move or be copied from one site to another in the genome are called

The ________ approach to gene cloning employs a mixture of fragments from the entire genome of an organism.

Molecule, cell, tissue, organ, organ system, organism, population, community, ecosystem

Life is organized in a hierarchical fashion. Which of the following sequences correctly lists that hierarchy as it increases in complexity?

The tree in your backyard is home to 2 cardinals, a colony of ants, a wasp’s nest, two squirrels, and millions of bacteria. Together, all of these organisms represent

The ultimate source of energy flowing into nearly all ecosystems is

Your instructor asks you to look into your microscope to see a prokaryotic cell. You will be looking for a cell that

Which of the following is a kingdom within the domain Eukarya?

You notice that over the past month, many students on campus have started wearing a new style of school sweatshirt. You think to yourself that perhaps the bookstore has recently started selling this new sweatshirt style. This prediction is an example of

The sum of all Earth’s ecosystems is called the

While on a walk through a forest, you notice birds in trees, earthworms in the soil, and fungi on plant litter on the forest floor. Based on your observations, ou concluded that each of these organisms occupies a different

The level of ecologic organization that incorporates abiotic factors is the

environmental effects of pesticides

Rachel Carson’s book, Silent Spring, deals with the

Rises and cools, dropping rain

In terms of global air circulation, the tropics are in a region where air

If you travel from west to east through Ecuador, you will pass through tundra, taiga, temperate forest, and tropical rainforest. Which of the following climatic factors remains constant on such trip

scarcity of rain on the eastern flank and adjacent lowlands compared to the western flank.

When people speak of the "rain shadow" of the California /coast Range, they are reffering to the

A sperm whale in the middle of the Atlantic Ocean is in which oceanic zone?

In many dense forests, plants living near the ground level engage in intense competition for

Fresh water and sea water mix in a(n)

Tundra- very cold winters only the upper layer of the soil thaws during summer

Whoch of the following opinions correctly pairs a biome and its characteristics?

Many desert aminals are nocturnal.

Which of the following statements about deserts and the organisms that live there is true?

Chaparral vegetation occurs around much of the central valley of central and southern California. This biome is very similarto that found in

Many plantswith seeds that need fire to germinate.

Which of the following is a characteristic of the chaparral biome?

In which of the following biomes would you expect to find the highest abundance of large, grazing mammals?

Oak, hickory, birch, beech, and maple are common trees in temperate broadleaf forests.

Which of the following statements about temperate broadleaf forests is true?

Which of the following biomes is dominated by coniferous trees adapted to surviving long, harsh winters, and short wet summers?

Answers to questions about the immediate mechanisms for a behavior are called

The evolutionary expectations for behavior are called

When a nipple is placed in a newborn baby’s mouth, the infant will immediately begin to suckle. This is an

When you successfully study with music on in the background, you are demonstrating

Agrayling butterfly will normally fly towards the sun. This is an example of

Squirrels on a bird feeder seem to be able to figure out how to steal seeds no matter what people do to prevent it. Yesterday, Jeremy hung out a new bird feeder design, and sure enough, by the end of the day the squirrels found a way to get to the seeds. The squirrels most likely figured out how to get the seeds through

The baby bobcat watched as their mother stalked a rabbit and pounced, catching a meal that was shared by all. The next day,two of the young bobcats were stalking a field mouse, which quickly escaped the inexperienced hunters. The young bobcats were learning how to hunt by the process of

Imitation is not limited to a sensative period

A big difference between imitation (social learning) and imprinting is that

You think about what color clothing she wore, and look for that color.

You lose track of your friend in a store and start looking for her. Which of the following things that you could do represents the use of a search image

The sending of, reception of, and response to signals constitute animal

Organisms that are nocturnal are more likely to communicate using

The individuals are fertile and of the opposite sex.

Which of the following is communicated by courtship displays

A dog raises its hackles, bares its teeth, and stands high to appear threatening

Which of the following would be an example of agonistic behavior

Is used to establish dominance hierarchies.

Pecking order in chickens is an example of

An adult human jumps into a raging river to try to save a child who is drowning and is unrelated to the adult. This is an example of

You help your brother pay for his children’s college tuition, even though he may not be able to pay you back.

Which of the following situations could represent kin selection in action

A survivorship curve that involves producing very few offspring, each of which has a high probability of surviving to adulthood, is typical of

In the 2000 years thats humans have lived on Madagascar, the island has lost approximately what percent of its native species.

The primary decomposers of a community are called

Within an ecosystem, a tree is a

DDT released into the environment

Large coastal dead zones depleted of oxygen are primarily caused by

In a hypothetical food chain consisting of grass, grasshoppers,sparrows, and hawks, the grasshoppers are

Attempt to restore the natural wetlands associated with the Kissimmee River

The Kissimmee River Project is an

Carbon dioxide traps heat and warms the atmosphere. This is known as the ______ effect.

The pattern of distribution for a species of kelp is clumped. We would expect that the pattern of distribution for a population of snails that live on the kelp would be

Nitrogen-fixing bacteria convert atmosphereic nitrogen to ammonia.

Which of the following represents a step in the nitrogen cycle?

The nitrogen cycle requires different types of bacteria.

Which of the following statements about the nitrogen cycle is true?

An owl and a hawk both eat mice. Which of these terms describes the relationship between a hawk and an owl?

A polar bear producing one or two cubs every three years.

Which of the following organisms best illustrates K-selection?

Booby and noddy birds, primary consumers.

A hypothetical community on a barren mid-Atlantic island consists of two fish-eating seabirds (the booby and the noddy), the fungi and microorganisms that live on the birds dung, a tick that feeds on these two birds, a cactus, a moth that feeds on cast-off feathers, a beetle that lives on dung organisms, and spiders that eat the arthropods. There are no other plants and no lichen. Which of the following choices incorrectly pairs a member of the assemlage with its poition in the trophic structure?

When two different populations in a community benefit from their relationship with each other, the result is called

Which of the following is an introduced species in the United States

The movement from high birth rates and high death rates to low birth rates and low death rates is calledd demographic transition.

Which of the following statements about human demographic trends is true?

Assume that there are five alligators per acre in a swamp in northern Florida. This is a measure of the alligator population’s

Potentially interacting populations of different kinds of organisms.

A community is composed of

The maximum number of individuals a habitat can support is called its

A group of individuals of a single species that occupy the same general area defines a

The sum total of a population’s use of the biotic and abiotic resources of its habitat constitutes its

Denitrifying bacteria convert ________ to ________.

Habitat destruction due to humans

Currently, the single greatest threat to biodiversity is

Elimination of flying insects

Which of the following is a likely consequence of the thinning of the ozone layer?

Parents providing extended care for their young.

A type 1 survivorship curve is the result of which of the following life history traits?

One mechanim that prey populations evolve to avoid predation is

Changes gradually because each species responds differently to the changing environment.

During ecological succession, the species composition of a plant community generally

A newly mated queen ant establishes an ant nest in an unoccupied patch of suitable habitat. Assuming that no disasters strike the nest, which of the following types of equation will best descibe its population growth?

The number of species in a community is called the

In a food chain consisting of phytoplankton -> zooplankton -> fish -> fishermen, the fishermen are

One species will take over most or all of the zone of overlap.

If an overlap develops between the ranges of two closely related species, and if the species occupy the same niche in the zone of overlap, what will probably happen in the zone of overlap?

If there are 1,000 metric tons of producers in an ecosystem, about how much of the energy in those producers will be available to secondary consumers in this ecosystem?

You want to do al that you can to safeguard the environment by preserving energy. One simple thing that you can do is to eat a diet consisting only of organisms that are

Produce energy that is used by coral animals through photosynthesis.

Dinoflagellates are important to coral and coral-dwelling animals because they

A shortage of calcium in the soil.

It appears that forest plant growth at Hubbard Brook halted because of acid rain and snow that caused

Water runoff increased in the deforested areas.

In experimental studies conducted at the Hubbard Brook Experimental Forest, it was found that

Take advantage of human activity, such as clearing woodlots.

The life history strategy of an r-selected species is to

The genetic diversity within and between populations of a species.

The intentional release of a natural enemy of a pest population.

Biological control is defined as

CO2 flooding into the atmosphere is absorbed by ________ and converted into biomass.

Rates decline and/ or death rates increase.

In the logistic growth model, as population size increases, birth rates

You drive through Iowa in the spring, and notice that along a stretch of several kilometers, every thrid fence post has a male redwing blackbird perched on it defending its nesting territory. This is an example of

CO2 is converted in photosynthesis to carbohydrates.

Given that CO2 is produced by respiration, why does the amount of CO2 in the atmosphere remain relatively constant? ( When answering this question, exclude the impact of human activities on atmosphereic CO2

When a New England farmer is abandoned, its formerly plowed fields first became weedy meadows, then shrubby areas, and finally forest. This sequence of plant communities is an example of

Through mutations or changes in the expression of one or a few "master control" genes that regulate development.

According to "evo-devo" thinking, an organism’s body form can be substantially changed

________ are membranes containing concentrated organic molecules and have some lifelike properties, but are not alive.

Which of the following type of reproductive barriers separates two species of sea cucumbers, whose sperm and eggs often bump into each other but do not cross-fertilize because of incompatible proteins on their surfaces?

Genetic drift resulting from a disaster that drastically reduces population size is called

Speciation without geographic isolation is called ________ speciation.

You have sampled a population of shmoos in a deep cave isolated from sounds. You discover that in these shmoos, blue eye i a recessive allel, and the frequency of blue-eyed shmoos is 0.36. Assuming Hardy-Weinberg equilibrium, what is the frequency of the blue eye allele?

Thirty people are selected for a long-term mission to colonize a planet many light years away from Earth. The mission is successful and the population rapidly grows to several hundred individuals. However, certain genetic diseases are unusually common in this group, and their gene pool is quite different from that of the Earth population they have left behind. Which of the following phenomena has left its mark of this population?

You find the frozen remains of a wooly mammoth in an Alaskan glacier. You analyze a bit of the tusk and find that its 14C: 12C ratio is about one-fourth of the baseline level typically found in living organisms. Given that the half-life of 14C is 5730 years, when did the mammoth die?

Differential reproductive success based on inherited characteristics

Which of the following best expresses the concept of natural selection?

Have the potential to interbreed in nature and produce fertile offspring.

A biological species is defined as a group of organsms that

Organisms that possess more than two complete stes of chromosomes are said to be

Two species that sometimes mate and produce vigorous but sterile offspring are separated by

Which of the following types of reproductive barriers separates two flowering plants species that could interbreed except that one has a deep flower tube and is pollinated by bumblebees, whereas the other has a short, narrow flower tube and is pollinated by honeybees?

Mutation in parent cells (asexual organisms) or in cells that produce gametes (sexual organisms)

The ultimate source of all new alleles is

It is fully decomposed by bacteria and fungi.

Which of the following would prevent an organism from becoming part of the fossil record when it dies?

The emergence of a new plant species over a brief period of time, followed by a long period of little change, is consistent with which of the following theories?

First prokaryotes photosynthesis first eukaryotes colonization of land by plants and fungi.

Which of the following options lists major events in the history of life on Earth in the proper order, from earliest to the most recent?

Earth’s land masses have joined into a single continent and split back apart again on three occasion.

Geologists have evidence that over the past 1.5 billion years

Self-replicating RNA molecules aided by ribozymes.

A current leading hypothesis about the first system of inheritance in the earliest life forms involves

The collision of two continental plates.

The Himalayas are an example of a mountain range formed as a result of

The atmosphere was rich in gases released in volcanic eruptions volcanic activity, lightening, and ultraviolet radiation were all much more intense than on today’s Earth.

When the Earth first solidified, what were conditions like?

Broccoli, cabbages, and brussels sprouts akk descend from the same wild mustard and can still interbreed. These varieties were produced by

Descent with modification occurs through inheritance of aquired characteristics.

Which of the following statements would Darwin have disagreed with?

One-sixteenth of the original amount.

If an isotope has a half-life of 4 million years, and a fossil is 16 million years old, how much of the original isotope will be found in the fossil?

A population’a allele frequencies change over a span of generations.

Microevolution, or evolution in its smallest scale, occurs when

The geographic isolation of a population from other members of the species and the subsequent evolution of reproductive barriers between it and the parent species describes__________.

Frequency, a group of related species will each have a unique courtship ritual that must be performed correctly for both partners to be willing to mate. Such a ritual constitues a _________, _________reproductive barrier.

Little gene flow with surrounding population.

Which of the following conditons would tend to make the Hardy-Weinberg equation more accurate for predicting the genotype frequencies of the future generations in a population of a sexually reproducing species?

Prokaryotes….3.5 billion years ago.

The earliest discovered fossils are of ______, dating back to _______ years ago.

The wing of a bat and the flipper of a whale.

Which of the following represents a pair of homologous structures?

Which of the following types of reproductive barriers separates a pair of species that could interbreed except that one mates at dusk and the other mates at dawn?

She should continue taking the drug until her immune system can completely eliminate the infection. Otherwise the remaining bacteria in her system may recover, and they will probably be resistant.

A woman struggling with a bacterial illness is prescribed a month’s supply of a potent antibiotic. She takes the antibiotic for about two weeks and feels much better. Should she save the remaining two weeks supply, or should she continue taking the drug?

The recessive allele of a gene causes cycstic fibrosis. For this gene among Caucasians, p= 0.98. If a Caucasian population is in Hardy-Weinberg equilibrium with respect to this gene, what proportion of babies is born homozygous recessive, and therefore suffers cystic fibrosis?

Which of the following will tend to produce adaptive changes in populations?

Which highly reactive gas was probably absent from the Earth’s primative atmosphere?

During the _______, over 96% of marine species and many terrestrial species became extinct probably because intense volcanic activity warmed Earth’s climate.

The mass extinction of dinosaurs, an event that opened up new ecological oppertunities.

Scientists believe that a major factor promoting the adaptive radiation of mammals was probably

Which of the following thinkers argued that organisms tnd to produce many more offspring than the environment can support, leading to a struggle for existance, an argument the later influenced Charles Darwin’s ideas of natural selection?

Heritable traits that promote reproduction become more frequent in a population from one generation to the next.

Which sentence best describes the true nature of natural selection?

Complex organic molecules can be produced by physical processes from inorganic components.

Miller-Urey-type experiments have shown that

Oxygen gas tends to disrupt organic molecules, so its absence promoted the formation and stability of complex organic molecules on the early Earth.

Whar was the probable role of oxygen gas in the early stages of life’s apperance on Earth?

An organism colonizes an isolated area that is habitable but relatively devoid of life.

Which of the following would tend to promote adaptive radiation?

Presence of flagellated sperm

Which of the following characteristics tends to limit bryophytes and seedless vascular plants to habitat that are relatively moist?

From carbon dioxide in the atmosphere

Where do plants get most of their mass?

Ferns have well-developed vascular tissue, roots, and stems.

Which of the following statements regarding ferns is true?

White potatoes are modified plant roots.

Which of the following statements is false?

Unlike archaean and eukaryote cell walls, bacterial cell walls contain a unique substance called

basidiomycetes (club fungi)

Most familiar types of mushrooms, along with puffballs andshelf fungi, are

Marine and freshwater algae that can produce harmful red tides.

Dinoflagellates are best described as

The pull on water from dry air

Which of the following produce the greatest amout of transpiration-cohesion-tension force?

There is a good chance you will eat carrageenan today, and you will eat nori at some point in your life, if you haven’t already. In either case, you will be eating a product of

The inner cell will differenciate into the xylem, and the outer cell will divide again.

A vascular cambrium cell divides to produce an inner and an outer daughter cell. Which of the following represents the probable fate of these cells?

Diploid sporophytes that produce spores by meiosis alternate with haploid gametophytes that produce gametes by mitosis.

Which of the following statements correctly decribes the alternation of generation in a plant life cycle?

Is an above-ground fruiting body connected to a mycelium.

Plant roots absorb carbon dioxide needed for photosynthesis from the soil.

Which of the following statements is false about plant roots?

Increase the surface area for absorbsion of water and minerals.

The chief function of root hairs is to

Are similar to bacteria because fungi useextracellular digestion to obtain their nutrients.

Which of the following essential macronutrient for plants is obtained directly from the air?

Long-distance water conduction

Which of the following is a function of sclerenchyma cells?

The type of plant vascular tissue specialized to conduct foods such as sugars is known as

You collect a protist from a rotting log and grow it in a petri dish containing E coli, which it engulfs. For a while the protist multiplying as single cells. Then the E coli. run short, and the protist aggregate to form a clump, which rises up to become a stalked structure with a globular hear. What kind of protist have you got?

Which of the following substances, by providing strength, allows some of a plant’s vascular tissue to provide support and play a role analogous to that of an animal’s skeleton?

_______ are toxic proteins secreted by pathogenic bacteria, whereas _______ are componentes of the outer membrane of gram-negative pathogens.

Corn, rice, wheat, fleshy fruits such as apples and berries, and many species are all produced by

Giardia, a parasitic diplomonad

While on a camping trip, you drink untreated stream water. After a few days you develop severe diarrhea. Microscopic examination of a fecal sample from you is mot likely to reveal

Which of the following is a characteristic of eudicots?

Green algae similar to charophytes….coastal marshes or lake fringes

The ancestors of land plants were probably ______ that lived in _______.

Membrane-enclosed sacs under the plasma membrane.

Alveolates are characterized by

Prokaryote genomes ofter include a central ring of DNA plus small acessory rings of DNA that carry genes involved in "coningency" functions. These secondary rings of DNA are called

What is the physical barrier in the root that regulates the flow of water to xylem via cell walls?

The male organ of a flower is the

Passing wastewater through a thick bed of rocks. Biofilms of bacteria and fungi on the rocks absorb and decompose organic material dissolved in wastewater.

The trickling filter at a sewage plant works by

Pushed through pholem and pulled through xylem.

Genreally speaking, fluids in plants are

Pili= help prokaryotes stick to each other and to surfaces

Which of the following options correctly pairs a structure with its function in prokaryote cells?

Two characteristic shared by gymnosperms and angiosperms that are absent from earlier plant groups and represent key adaptations to life on dry land are

The loading of sugars into phloem at sources and removal of sugars at sinks.

The exisistance of a hydrostatic pressure gradient in phloem tubes can be accounted for by

Nitrogen is added to the soil by nitrogen-fixing bacteria.

Legumes are frequently grown in rotation with primary field crops. What is the benefit in this?

Flowers bear seeds that develop from ovules housed in protective chambers called

Cell elongation behind the apical meristem

The growth that pushes a root down through the soil takes place through

At the surface of plant organs

In general, plant dermal tissue is found

A patient cpmes to the doctor with a large red rash, shaped like a bull’s-eye with a clear patch in the center. Originally there wa a tick bite in the middle of the rash. The patient lives in a suburban area of the United States where deer are common. Which of the following diseases will the physician immediately suspect?

The genetically identical organisms that reult from asexual reproduction are called

In angiosprems, the process of________ ensures that the endosperm will develop only in ovules containing a fertilized egg.

Which type of vascular tissue in a plant is dead at maturity?

An association between a fungus and cyanobacteria or green algae

What kind of entity is a lichen?

Gangrene, hallucinations, temporary insanity, and even death can result when humans consume grain infested with

K+ enters the guard cells and water follows passively, making the cells turgid

Which of the following options best describes the mechanism that causes the stoma to open?

The most ancesteral (ancient) extant (surviving) tetrapods are ______ derived from_______.

______ were the first clearly bipedal hominids.

The need to block UV radiation that destroys folate and the need to synthesize Vitamin D.

Human skin color likely represent a locally adapted compromise between

Which of the following groups includes both spiders and horseshoe crab?

Recall that cuticle seals plant surfaces and helps plants conserve water and that the seed helps derived plant groups to reproduce effectively on dry land. The analogous adaptations in reptiles are_____ (analogous to cuticle) and ______ (analogous to the seed)

________ are known to make and use simple tools.

The last common ancestor shared by humans and chimpanzees lived about

Walking in a basement you hear a crunching moise and notice that you have killed a small animal. You look closely ans see a few segmented, jointed appendages twitching around. Which phylum does this animal represent?

The _______ is a flagellated cell that sweeps water through a sponge’s body.

Which of the following organisms is a marsupial?

While wading in the ocean, you look down into the water and notice an umbrella-shaped translucent animal. It swims by pushing its body, and long tenticles trail behind it. One of them brushes your leg. Ouch! You feel a burning sensation where it touched you. To what phylum does this creature probably belong to?

Have hair and mammory glands

A dog’s hea is at it ________ end and its belly is its ______ surface.

Natural population of lemurs are currently found only in

Typical animal embryos have______, or external cell layers, and ________, which lines the digestive tract.

The duck-billed platypus and other monotremes differ from other mammals in that they

Prehensile tails are found among

According to the fossil record, the genus homo first arose in

An organism that can fly and has an exoskeleton must be

The digestive tract of a nematode is most like which of the following

Animals probably evolve from

The first vertebrate with a head and skull probably reembled a

______ is thought to have played a cuticle role in the evolution of human speech.

A group of feathered, endothermic dinosaurs that survived the Cretaceous mass extinction.

Which of the following statements best describes the current scientific view of birds?

________ and soil-dwellers _____ are mostly marine and ______ are mostly freshwater.

Two pairs of skeletal rods that supported gill slit near the mouth.

Jaws appear to have evolved from

The earliest hominid to be found outside of Africa belongs to which species?

A rasoing organ called the radula.

Which of the following is a typical characteristic of molluscs?

Which of the following is an invertebrate chordate?

Which animals are or may have been endothermic?

Which of the following animals displays radial symmetry?

Which of the following adaptations allowed reptiles to complete their life cycles on land?

A body cavity that is fully lined by tissue derived from the mesoderm.

A true coelom is best described as

Unlike sharks and rays,ray-finned fishes have

Ectotherms obtain body heat from external sources, but endotherms use metabolic heat to maintain a warm, steady body temperature.

Which of the following statements best summarizes the differences between ectothermic and endothermic organisms?

The opening formed during gastulation became the mouth.

Which of the following structures best represents a hydrostatic skeleton?

Craniates are chordates that all possess

Sahelanthropus, Australpithecus, Homo habilis, Homo sapiens

Which of the following options lists the major groups or genera from the fossil record in the proper order from earliest to most recent?

Lack jaws and paired fins

Lampreys differ from fishes in that Lampreys

Which of the following animal groups is characterized by an absence of tails and forelimbs that are generally longer than their hind limbs?

Blue-footed boobies have webbed feet and are comically clumsy when they walk on land. Evolutionary scientists view these feet as

the outcome of a tradeoff: webbed feet perform poorly on land, but are very helpful in diving for food.

Which of the following statements would Darwin have disagreed with?

Descent with modification occurs through inheritance of acquired characteristics

Broccoli, cabbages, and Brussels sprouts all descend from the same wild mustard and can still interbreed. These varieties were produced by.

Humans share several features with salamanders. Certain genes and proteins are nearly identical between the two species: both species have four limbs with a similar skeletal structure the species vestigial tailbone. In evolutionary terms, these are examples of

Darwin was the first person to draw an evolutionary tree, a diagram that represents

evidence- based hypotheses regarding our understanding of patterns of evolutionary descent.

Which sentence best describes the true nature of natural selection?

Heritable traits that promote reproduction become more frequent in a population from one generation to the next.

An elk herd is observed over many generations. Most of the full-grown bull elk have antlers of nearly the same size. The average antler size remains constant over the generations. Which of the following effects probably accounts for the situation?

A women struggling with bacterial illness is prescribed a months supply of a potent antibiotic. She takes the antibiotic for about 2 weeks and feels much better. Should she save the remaining two week supply or should she continue taking the drug?

She should continue taking the drug until her immune system can completely eliminate the infection. Otherwise the remaining bacteria in her system may recover, and they will probably be resistant

The sickle-cell allele produces a serious blood disease in homozygotes. Why doesn’t natural selection eliminate this allele from all human populations?

In populations were endemic malaria is present, heterozygotes have an important advantage: They are resistant to malaria and therefore are more likely to survive and produce offspring that carry the allele.

Frequency-dependent selection, as seen in the case of the scale-eating fish in lake Tanganyika, tends to

maintain two phenotypes in a dynamic equilibrium in a population

During which of the following stages of food processing is undigested material removed from the digestive tract

An alimentary canal is best defined as

a tube-shaped compartment for the transport, digestion, and absorption of food

Which of the following correctly lists the order of the parts of the human digestive system, from first to last contact with food matter?

oral cavity, pharynx, esophagus, stomach, small intestine, large intestine

The mucous-producing cells that line the stomach

lubricate and protect the stomach lining

In the digestive system, most nutrient absorption occurs in the

organisms suffering from malnutrition may have a diet deficient in

one or more essential nutrients

which of the following is a hormone produced by adipose cells that help to control appetite?

Animals that maintain internal body temperature using heat generated by their own metabolism are called

To enhance heat loss, humans sweat, an adaption known as

sweating commonly results in dehydration. Of the choices listed, which would be the best option for rehydration after intense exercise?

mammals have evolved a sophisticated mechanism for eliminating nitrogenous wastes that involves

forming urea and storing it in concentrated solution

whats is the name of the functional unit of the kidneys

during production of urine, a major function of the kidney is

what is the function of antidiurectic hormone?

to increase water reabsorption

when a salmon moves from the ocean to a freshwater environment, you would expect its urine volume to _______ and its rate of salt absorption to ______.

In a dialysis machine, wastes are removed from blood plasma by process of

through which of the following structures does urine leave the bladder?

increased brain size had many benefits for early humans. one example is

complex social structure with the ability to adapt to changing environments

when comparing the differences between human and chimpanzee DNA

the differences are generally found in the gene switches that determine when and how genes are expressed.

walking upright has both pros and cons. some of the pros of walking upright include

looking large to predators, the ability to harvest more food, the ability to carry young.

homo erectus was the first early human to spend most of its time walking upright

tool use is uniquely human

chimpanzees are humans closest living relatives

lower back pain can be attributed to walking upright, which formed the curvature at the base of the spine

Humans and chimpanzees have 90% identical genome sequences

Darwins ideas about evolution were formed after observing marine iguanas on the galapagos islands

____ genes are responsible for coding for self-proteins.

A molecule that can elicit an adaptive immune response is called

Medullary breathing centers directly sense and respond to

blood pH and CO2 concentration

which part of the diagram shows the alveoli?

Air leaving human lung during exhalation contains

carbon dioxide and unused oxygen

during gas exchange, body cells

release CO2 and take in O2

As blood moves away from the heart towards the tissues, the relative size of blood vessels _____, the blood pressure ______, and the velocity of blood flow _______.

which of the following is a function of the nasal cavities in humans?

arteries are distinguished from veins based on all of the following features except

the amount of oxygen present in the blood

The main function of the AV node is to

relay a signal for the ventricles to contract

The maximum amount of air that a human can inhale and exhale is called the

Which of the following cell types is responsible for the cell-mediated immune response?

attack virus-infected cells by releasing chemicals that lead to the death of the cell

Oxygen moves from blood into the interstitial fluid and then to body cells because

it diffuses from a region of higher partial pressure to a region of lower partial pressure

which of the following distingueshes the secondary immune response from the primary?

The secondary response is faster and stronger

which of the following choices best describes a plasma cell?

It is a differentiated B cell

Oxygen-poor blood is carried from the heart of a mammal to the lungs via the

What type of blood vessel is solely responsible for exchange between the blood and the interstitial fluid?

which of the following helps activate our nonspecific (innate) defense system?

A primary immune response is

the immune response elicited by the first exposure of lymphocytes to a particular antigen

cardiac output is defined as the volume of blood pumped by an ____ each time it contracts

Which of the following types of cells does HIV preferentially infect?

The reason animals need continuous supply of oxygen is

obtain energy from their food

after binding to an infected cell, the cytotoxic T cell

releases a protein called perforin

what part of the human brain contains the primary breathing control center?

multipotent stem cells found in the red marrow inside bones

can differentiate into all blood cells and platelets

An adult humans red blood cells are formed in the

which blood vessels have the thinnest walls

labored breathing, coughing, lung infections, and respiratory failure are characteristics defining

chronic obstructive pulmonary diseases

which of the following contributes to gas exchange in the human fetus

the stronger attraction that fetal hemoglobin has for oxygen when compared to adult hemoglobin

blood clots are formed by platelets and the plasma protein

which of the following statements about mammalian circulatory systems is false?

The left side of a mammals heart sends blood to the lungs

The liquid part of blood is called

what prompts a newborn baby to start to breather?

an increase in the concentration of oxygen in the baby’s blood

which of the following options correctly lists the direction of carbon dioxide travel as it leaves the body?

alveoli, bronchioles, bronchi, trachea, larynx, pharynx

which of the following is a function of the circulatory system?

transporting nutrients to body cells

The oxygen-carrying component in red blood cells is

which of the following wander through the interstitial fluid and consume any bacteria and virus-infected cells they encounter?

anaphylactic shock is an example of an

which of the following cells are phagocytes?

monocytes and neutrophils

which of the following can contribute to high blood pressure?

blood flow through capillaries is controlled by

precapillary sphincters and smooth muscle in the walls of arterioles

what type of immune response is always disadvantageous to a person?

which of the following cell types is responsible for the humoral immune response?

The human lymphatic system consists of all of the following structures except the

The basic function of the activated T cells is to battle

pathogens that have alreasy entered body cells

one kind of vaccine consists of

a harmless variant strain of a disease-causing microbe

cigarette smoke can affect the white blood cells that reside in our lungs, whose purpose is to

which of the following animals requires the largest and most complex lungs proportional to its overall body size?

Plasma proteins are involved in all of the following activities except

The autonomic nervous system

regulates the internal environment of the body

The central communication conduit between the brain and the rest of the body is the

functionally, the muscle fibers fundamental unit for contraction is the

muscles are connected to the bones by

a tennis player serving the ball uses fast muscle fibers. The ATP needed to accomplish this would come from

The signal that crosses a synapse is stopped when

the neurotransmitter is enzymatically broken down or transported back to the signaling cell

living cells that secrete a surrounding matrix

the neurotransmitter found at the synapse between nerves and human skeletal muscle cells is

which division of the human nervous system carries signals to skeletal muscles?

action potentials normally travel along an axon

According to the sliding filament model of muscle contraction, a sarcomere contracts when its

thin filaments slie towards each other across its thick filaments

work in antagonistic pairs

nervous system effector cells

include muscle cells and gland cells

which of the following statements regarding the brain is true

the blood-brain barrier helps to maintain a stable chemical environment for the brain

the gap between the transmitting and receiving neurons in a chemical synapse is known as the

The relationship between spinal nerves and the spinal cord is most like the relationship between

an interstate highway and the many roads that intersect with it via on- and off- ramps

which of the following structures constitutes part of the axial skeleton

The calcium that triggers muscle contraction is stored in

the endoplasmic reticulum

which of the following statements regarding exercise is true

the main source of energy during aerobic exercise is ATP from aerobic respiration

Osteoporosis is characterized by

low bone mass and structural deterioration of the bone tissue.

what part of the neuron carries signals toward the part of the cell that houses the nucleus

one neurotransmitter associated with sleep, mood, attention, and learning is

Muscles that are constantly active, such as those maintaining our body posture, having a high proportion of

slow, fatigue-resistant fibers.

Parkinsons disease is associated with a deficiency in

which of the following statements regarding the nervous system is true

motor neurons convey signals from the CNS to the effector cells

which of the following statements about resting potential is true

the sodium-potassium pump contributes to the resting membrane potential

changes occur within a sarcomere during muscle contraction. one change is that the

Z lines move closer together

The shoulder joint where the humerus meets the shoulder gridle is an example of

a motor neuron and all of the muscle fibers it controls

The speed of impulse conduction along an axon may be increase by

Neurotransmitters that open Na+ channels and trigger action potentials in receiving cells are called

The enteric division of the autonomic nervous system consists of neurons in the digestive tract, the gallbladder and

a thick filament consists of

which of the following statements about locomotion is true

locomotion requires animals to overcome friction and gravity

multiple sclerosis results from an autoimmune disease that primarily involves

destruction of the myelin sheath

which of the following statements best describes the power stroke of muscle contraction?

the myosin head bends, pulling the thin filament toward the center of the sarcomere

which part of a bone contains mostly stored fat?

during transmission across a typical chemical synapse

neurotransmitter molecules bind to receptors in the receiving cells plasma membrane

the functional unit of the nervous system is the

in all vertebrates, the brain consists of the

the sequence of events that cause a muscle to contract can be summed up in the correct order as

detach, extend, attach, pull

the contacting surfaces of a moving joint, such as your hip joint, consist of

action potentials relay different intensities of information due to the

frequency of action potentials relative to the strength of the stimulus

which of the following statements about skeletal muscle fibers is true

each muscle fiber contains actin and myosin

the two major anatomical divisions of the nervous system are the

central nervous system and peripheral nervous system

Which of the following statements regarding sexual reproduction is true?

Sexual reproduction generates greater genetic variation than asexual reproduction.

In which part of the human female reproductive system does fertilization normally take place?

Human testes are positioned in an external sac rather than in the abdominal cavity

so the testes can be kept cooler than the body’s interior.

Which of the following produces a thick fluid containing fructose, which is used for energy by sperm?

Which of the following statements comparing spermatogenesis and oogenesis is true?

Men, but not women, can produce gametes throughout their lives.

Which of the following STDs is caused by a virus that can also cause cancer?

Sterilization, in which the sperm is surgically prevented from reaching the egg, is accomplished by

tubal ligation or vasectomy.

The function of a sperm cell’s acrosome is to

carry enzymes that help the sperm penetrate the egg.

Which of the following serves as an impenetrable barrier that prevents more than one sperm from fertilizing an egg?

Which of the following occurs during the process of labor?

positive feedback involving oxytocin and prostaglandins

Mendel conducted his most memorable experiments on

An insect that has the genotype EeGGcc will have the same phenotype as an insect with the genotype _____.

In an individual of genotype Aa, where are the A and a alleles physically located?

One allele is on one chromosome, and the other is in the same position (locus) on the homologous chromosome.

The phenotypic ratio resulting from a dihybrid cross showing independent assortment is expected to be

Imagine that we mate two black Labrador dogs with normal vision and find that three of the puppies are like the parents, but one puppy is chocolate with normal vision and another is black with PRA (progressive retinal atrophy, a serious disease of vision). We can conclude that

the alleles for color and vision segregate independently during gamete formation.

Imagine that long fins in zebrafish is a dominant trait. A breeder wants to set up a breeding program beginning with homozygous dominant long-finned fish. If she obtains a handful of the long-finned fish, how can she tell which if any of these are homozygous for the trait?

Cross the long-finned fish with short-finned fish if the offspring are all long-finned, the long-finned parent is homozygous.

Dr. Smith’s parents have normal hearing. However, Dr. Smith has an inherited form of deafness. Deafness is a recessive trait that is associated with the abnormal allele d. The normal allele at this locus, associated with normal hearing, is D. Dr. Smith’s parents could have which of the following genotypes?

A carrier of a genetic disorder who does not show symptoms is most likely to be ________ to transmit it to offspring.

heterozygous for the trait and able

All the offspring of a cross between a red-flowered plant and a white-flowered plant have pink flowers. This means that the allele for red flowers is ________ to the allele for white flowers.

A woman has been trying to conceive for several years, unsuccessfully. At a fertility clinic, they discover that she has blocked fallopian tubes. Using modern technologies, some of her eggs are removed, fertilized with her husband’s sperm, and implanted into her uterus. The procedure is successful, but the couple discovers that their new son is color-blind and has blood type O. The woman claims that the child can’t be theirs since she has blood type A and her husband has type B. Also, neither parent is color-blind, although one grandparent (the woman’s father) is also color-blind.

As a genetic counselor, you would explain to the parents that

it is possible for the baby to have type O blood, since type O is inherited through a dominant allele.

has been around since the dawn of civilization.

After DNA fragments with matching sticky ends are temporarily joined by complementary base-pairing, the union can be made permanent by the "pasting" enzyme

The type of recombinant bacteria most often used to mass-produce genes is

The advantage of being able to clone the gene for human insulin is that

human insulin is less likely to cause harmful side effects than cow, pig, or horse insulin.

Which of the following has not been a significant issue in the creation of genetically modified (GM) organisms?

the fact that GM organisms cannot be modified to prevent them from reproducing once they pass beyond the experimental stage

What is the preferred name of the technique used to determine if DNA comes from a particular individual?

Gel electrophoresis sorts DNA molecules on the basis of their

What is the current standard tool used for DNA profiling by forensic scientists?

Which of the following statements about genomics is false?

DNA technology limits genomic studies to prokaryotes.

In "Cracking Your Genetic Code," what type of cancer was being targeted with drugs based on the genome of the cancer cells?

A lot of your DNA is inherited "junk": It doesn’t code for any protein and has no known function in gene regulation. How do nucleotide sequences of "junk DNA" evolve?

They evolve through genetic drift and other chance processes.

After a copper smelter begins operation, local populations of plants downwind of the plant begin to adapt to the resulting air pollution. Scientists document, for example, that the acid tolerance of several plant species has increased significantly in polluted area. This is an example of a response to

What evidence is used to determine the branching sequence of an evolutionary tree?

anatomical or molecular homologous structures

the frequency of homozygous dominant individuals in a population that is in hardy-weinberg equilibrium is equal to

the frequency of homozygous dominant individuals in a population that is in hardy-weinberg equilibrium is equal to

in populations of the greater prairie chicken in Illinois, genetic diversity was.

Lost through genetic drift and restored by gene flow.

If you had to choose, where would you rather get infected with a serious bacterial disease.

In a remote, sparsely populated area where the bacteria have not been exposed to antibiotic drugs.

" Mothers and teachers have often said they need another pair of eyes on the backs of their heads. And another pair of hands would come in handy in many situations. You can imagine that these traits would have been advantageous to our early hunter-gatherer ancestors as well. According to sound evolutionary reasoning, what is the most likely explanation for why humans do not have these traits?"

Because these variations have probably never appeared in a healthy human. As tetrapods we are pretty much stuck with a four-limbed, two-eyed body plan natural selection can only edit existing variations.


Amphibians

In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs, toads, and newts all hatch from the eggs as larvae with external gills but it will take some time for the amphibians to interact outside with pulmonary respiration. Afterwards, newt larvae start a predatory lifestyle, while tadpoles mostly scrape food off surfaces with their horny tooth ridges.

Metamorphosis in amphibians is regulated by thyroxin concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts its effect. Specific events are dependent on threshold values for different tissues. Because most embryonic development is outside the parental body, development is subject to many adaptations due to specific ecological circumstances. For this reason tadpoles can have horny ridges for teeth, whiskers, and fins. They also make use of the lateral line organ. After metamorphosis, these organs become redundant and will be resorbed by controlled cell death, called apoptosis. The amount of adaptation to specific ecological circumstances is remarkable, with many discoveries still being made.

Frogs and toads

With frogs and toads, the external gills of the newly hatched tadpole are covered with a gill sac after a few days, and lungs are quickly formed. Front legs are formed under the gill sac, and hindlegs are visible a few days later. Following that there is usually a longer stage during which the tadpole lives off a vegetarian diet. Tadpoles use a relatively long, spiral‐shaped gut to digest that diet.

Rapid changes in the body can then be observed as the lifestyle of the frog changes completely. The spiral‐shaped mouth with horny tooth ridges is resorbed together with the spiral gut. The animal develops a big jaw, and its gills disappear along with its gill sac. Eyes and legs grow quickly, a tongue is formed, and all this is accompanied by associated changes in the neural networks (development of stereoscopic vision, loss of the lateral line system, etc.) All this can happen in about a day, so it is truly a metamorphosis (Figure 2). It is not until a few days later that the tail is reabsorbed, due to the higher thyroxin concentrations required for tail resorption.

Figure 2. (a) Just before metamorphosis, only 24 hours are needed to reach the stage in part b. (b) Almost functional common frog with some remains of the gill sac and a not fully developed jaw

Salamanders

Salamander development is highly diverse some species go through a dramatic reorganization when transitioning from aquatic larvae to terrestrial adults, while others, such as the Axolotl, display paedomorphosis and never develop into terrestrial adults. Within the genus Ambystoma, species have evolved to be paedomorphic several times, and paedomorphosis and complete development can both occur in some species. [2]

Newts

Figure 3. The large external gills of the crested newt

In newts, there is no true metamorphosis because newt larvae already feed as predators and continue doing so as adults. Newts’ gills are never covered by a gill sac (Figure 3) and will be resorbed only just before the animal leaves the water. Just as in tadpoles, their lungs are functional early, but newts use them less frequently than tadpoles. Newts often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxin. External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time.

Caecilians

Basal caecilians such as Ichthyophis go through a metamorphosis in which aquatic larva transition into fossorial adults, which involves a loss of the lateral line. [3] More recently diverged caecilians (the Teresomata) do not undergo an ontogenetic niche shift of this sort and are in general fossorial throughout their lives. Thus, most caecilians do not undergo an anuran-like metamorphosis. [4]


EVOLUTIONARY PRESSURES IN AMPHIBIANS

The lives of the most amphibians is divided into freshwater and land. Thus they show adaptations to both environments. The amphibians are supported by the buoyant of the water. They exchange gases with the water. They face the same osmoregulatory problems as freshwater fishes. On the other hand amphibian support themselves again gravity on land. They exchange gases with the air.

EXTERNAL STRUCTURE AND LOCOMOTION

Function: Vertebrate skin protects them from microorganisms, ultraviolet Light, dessication and mechanical injury. The skin of amphibians is used in gas exchange, temperature regulation, absorption and storage of water.

Skin glands:Amphibian skin lacks scales, feathers or hairs. However, it is highly glandular. It secretions protect the body. These glands keep the skin moist and prevent it from drying. They also produce sticky secretions. These secretions help male to attach with female during mating. It also produces toxic chemicals that discourage the predators. The skin of many amphibians is smooth. But some epidermal thickenings produce warts and claws. It makes the skin sandpapery. The deposition of keratin or the formation of hard, bony areas produces these warts.

Coloration: Chromatophores are specialized cells in the epidermis and dermis of the skin. They are responsible for skin color and color changes. Cryptic coloration (warning color), aposematic coloration (matching with the habitat) and mimicry are common in amphibians.

Support and Movement

Water buoys and supports aquatic animals. Their skeletons protect the internal organs and attach the muscles. It also prevents the body from collapsing during movement. However, there are different adaptations in terrestrial vertebrates. Their skeleton is modified to provide support against gravity. It is strong and it supports the powerful muscles.

Axia skeleton

The amphibian skull is flattened. It is relatively smaller. It has lesser bony elements than the skull of fishes. These changes lighten the skull. Thus body can support it easily. There are certain changes in jaw structure and musculature. Therefore, the terrestrial vertebrates can crush prey in the mouth.

2. Vertebral column

The vertebral column of amphibians provides support and flexibility on land. It supports the wight of the body between anterior and posterior paired appendage.

(a)Every vertebra has a supportive process called zygapophyses. It prevents the v wtebral column from twisting.

(b) The amphibians have a neck. The first vertebra is cervical vertebra. It moves against the back of the skull. It allows the head to nod vertically.

(c) The last trunk vertebra is a sacral vertebra. This vertebra attaches the pelvic girdle with the vertebral column.

(d) Sternum is present in the anterior entral trunk region. It supports the forelimbs and rotects internal organs. It is reduced cr absent in the Anura.

Fig: Skeletons of Amphibians. (a) The salamander skeleton is divided into four regions: cervical, trunk, sacral and caudal. (b) Interlocking processes, called zygapophyses. (c) A frog skeleton shows adaptations for jumping

Appendicular skeleton

The exact origin of the bones of vertebrate appendages is not known. However, similarities are present in the structure of the bone. of the amphibian appendages and the bones of the fins of ancient sarcopterygians fishes. It suggests homologies between these two. Joints are present at the shoulder, hip, elbow, knee, wrist and ankle. These joints allow freedom of movement. They also develop better contact between the body and the substrate.

The pelvic girdle of amphibians consists of three bones. T hese are ilium. ischium and pubis. These bones firmly attach pelvic appendages with the vertebral column. These bones are important for support on land. Tetrapods depend on appendages for locomotion. They do not depend on body wall for locomotion. Therefore, the body wall musculature is reduced and appendicular musculature has become strong.

Mode of locomotion

1. Salamanders: They have unspecialized form of locomotion. It is like undulatory waves in fish. Terrestrial salamanders also move with the help of limb and body movements. They show alternate movement of appendages and muscle contractions. It bends the body into a curve. This curve moves the limb forward.

2. Caecilians: They show an accordion (musical instrument)-like movement. In this case, adjacent body parts push or pull forward at the same time.

3. Anurans: The long hind limbs and the pelvic girdle of anurans are modified for jumping. The dorsal bone of the pelvis (the ilium) extends anterior. It is attached to the vertebral column. Their urostyle extends posterior and attaches to the pelvis. These skeletal modifications stiffen the posterior half of the anrans. Long hind limbs and powerful muscles are used for jumping efficiently. Pectoral girdle is attached to the skull and vertebral column by elastic connective tissues and muscles. These connective tissues are used as shock absorbers for landing on the forelimbs.

Fig: Salamander Locomotion

NUTRITION AND THE DIGESTIVE SYSTEM

Types of food

Most adult amphibians are carnivores. They feed on different invertebrates. Some anurans have more diverse diet. For example, a bull frog eats small mammals, birds and other anurans. The prey size and availability determine the type of diet. Most larvae are herbivorous. They feed on algae and other plant matter. Most amphibians locate their prey by, sight. They simply wait for prey to pass by it. Olfaction plays an important role in prey detection in aquatic salamanders and caecilians.

Mechanism of feeding

Many salamanders are unspecialized in their feeding methods. They use their jaws to capture prey. Anurans and plethodontid salamanders use their tongue and jaws in flip and grab feeding mechanism. A true tongue is first seen in amphibians. The amphibian tongue is attached at the anterior margin of the jaw. It folds back over the floor of the mouth. Mucous and buccal glands are present on the tip of the tongue. They release sticky secretions. When prey comes within range, an amphibian flicks out its tongue. The tongue turns over, and the lower jaw is depressed. The head tilts on its cervical vertebra. The tip of the tongue traps the prey. Then tongue and prey are licked back inside the mouth. All of this happens in 0.05 to 0.15 second. The amphibian holds the prey by pressing it against teeth on the roof of the mouth. The tongue and other muscles of the mouth push food towards the esophagus. The eyes sink downward during swallowing. They also push the food towards the esophagus.

CIRCULATION

GAS EXCHANGE AND TEMPERATURE REGULATION

Circulatory System

The circulatory system of amphibians is adapted for both aquatic and terrestrial habitats. The separation of pulmonary and systemic circuits is less efficient in amphibians than lung fishes. The atrium is partially divided in urodeles. It is completely divided in anurans. The ventricle has no septum. A spiral valve is present in the conus arteriosus. It directs the blood into pulmonary and systemic circuits.

Blood circulation to lungs: The exchange of gases takes place through the skin and lungs in amphibians. Therefore, blood entering the right side of the heart is also oxygenated. All gas exchange occurs through the skin and other moist surfaces when amphibians are in water. Therefore, blood in right atrium has a higher oxygen concentration than left atrium. Left atrium receives blood from the lungs. Therefore, blood vessels leading to the lungs constrict. It reduces blood flow to the lungs for conserving energy. The hibernating frogs and salamanders use this mechanism during their hibernation in winter.

Aortic arches: Adult amphibians have lesser aortic arches than fishes. The corms arteriosus give rises to three blood vessels:

1. Carotid artery (aortic arch III): It supplies blood to the head.

2. Systemic artery (aortic arch IV): It supplies blood the body.

3. Pulmonary artery (aortic arch VI): It carries blood to lungs.

Lymphatic system: The amphibians have a well developed lymphatic system. It is composed of blind ending vessels. It filters fluids, proteins and ion from capillaries in tissue spaces and returns them to the circulatory system. The lymphatic snstem also transports water absorbed across the skin. The amphibians have contractile vessels called lymphatic hearts. These hearts pump fluid through tile lymphatic system. Lymphatic system between the body wall muscles and the skin transport and store water. This water is absorbed through the skin.

Gas Exchange

Air contains 20 times more oxygen than water. Therefore, terrestrial animals spend less energy for gas-exchange than aquatic animals. But the exchanges of gases require moist surfaces. Thus terrestrial animal loss water during exposure of respiratory surfaces to air. There are three types of respirations in amphibians:

1. Cutaneous respiration: The skin of amphibians is kept moist. Amphibian skin is richly supplied with capillaries. Thus their skin functions as a respiratory organ. Gas exchange through the skin is called cutaneous respiration.

Cutaneous respiration can take place both in water and on land. This ability allows a frog to hibernate in winter. In salamanders, 30 to 90% of gas exchange occurs through the skin.

2. Buccopharyngeal respiration: Gas exchange can also take place through moist surfaces of the mouth and pharynx. It is called buccopharyngeaI respiration. It is only 1 to 7% of total gas exchange.

3. Pulmonary respiration: Most amphibians possess lungs. Lungs are absent in plethodontid salamanders. The lungs of salamanders are relatively simple sacs. The lungs of salamanders are subdivided into chambers. It increases the surface area for gas exchange. Pulmonary ventilation occurs by a buccal pump mechanism. Muscles of the mouth and pharynx create a positive pressure. This pressure forces air into the lungs.

Ratios of different methods of gas exchanges: Cutaneous and buccopharyngeal respiration have a disadvantage. Their percentage in the respirations is very small. The quantity of gas exchanged across these surfaces cannot be increased with increase in metabolic rate. However, lungs compensate this shortcoming. More gas exchange takes place through lungs with the increase of environmental temperature and activity. At 50 C, 70% of gas exchange occurs through the skin and mouth of a frog. At 25° C, the gas exchanged through skin and mouth remains the same. But pulmonary respiration increases. Now die exchange through skin and mouth is only about 30% of total oxygen exchange.

Gill: Amphibian larvae and some adults respire by external gills. Cartilaginous rods are present between embryonic pharyngeal slits. These rods support three pairs of gills. The gills are reabsorbed and pharyngeal slits are closed during metamorphosis and lungs become functional.

Temperature Regulation

Amphibians are ectothermic. They depend on external heat sources to maintain body temperature. Water has powerful heat-absorbing properties. Therefore, it quickly absorbs heat from aquatic amphibians. Thus their temperature becomes equal to the temperature of water. But their body temperatures can differ from the environment on land.

Temperature regulation is mainly behavioral. Amphibians have different adaptations for regulation of temperature:

1. They cool their body by evaporative heat loss.

2. Many amphibians are nocturnal.

3. They remain in cooler burrows or under moist leaf litter during the hottest part of the day.

4. Amphibians warm themselves by basking in the sun or on warm surfaces. Body temperatures may rise 100 degree centigrade above the air temperature. Metabolic reactions are increased with the increase in body temperature. Thus heat also -reases the functions of digestive system. Therefore, basking after a meal is mmon. It increases the growth. and the fat deposition Fat deposition is necessary r periods of dormancy.

The daily and the seasonal environmental temperatures of amphibians fluctuate widely. Therefore, amphibians have wide range of tolerance of temperature. Critical temperature for salamanders lie between 2 and 27oC. Critical temperature for some anurans is between 3 and 41° C.

NERVOUS AND SENSORY FUNCTIONS

Nervous system of amphibians is similar to that of other vertebrates. The brain of adult vertebrates develops from three embryological subdivisions. The brain of amphibians is divided into three parts:

1. Forebrain: It contains olfactory centers. It also has regions that control color change visceral functions.

2. Midbrain: It contains a region called the optic tectum. Optic tectum collects sensory i 111wmation and initiates motor responses. The midbrain also processes visual sensory information.

3. Hindbrain: It functions in motor coordination. It regulates heart rate and the respiration.

Serve organs

(i) Nerve endings

Sensory receptors are distributed over the skin in many amphibians. Some of these are bare nerve endings. These nerve endings respond to heat, cold, and pain.

(ii) Lateralline system:

Th also have lateral-line system like fishes. A lateral line system is present in all aquatic larvae, aquatic adult salamanders and some adult anurans. Lateral-line organs are present singly or in small groups. They are distributed in the lateral and dorsolateral surfaces of the body and on head. These receptors respond to low frequency vibrations in the water. Lateral line receptors are less important on land.

(iii Chemoreceptors

Chemoreception is an important sense in many amphibians. Chemoreceptors are present in the nasal epithelium, in the mouth, on the tongue, and over the skin. Olfaction is used in late recognition. It can detect toxic chemicals.

The amphibians are primarily sight feeders. Therefore, vision is the most important sense them. There are number of adaptations in the eyes of amphibians for terrestrial environments.

(a) The eyes of some amphibians are on the front of the head. It forms the binocular vision and well-developed image. This image is necessary for capturing prey.

(b) Other amphibians like some salamanders have smaller lateral eyes. They do not form binocular vision.

Structure of eye

The lower eyelid is movable in amphibians. It cleans and protects the eye. Its transparent part is called the nictitating membrane. The eyeball retracts into the orbit of the skull and the nictitating membrane covers the cornea. Amphibians also have orbital glands.

These glands lubricate and wash the eye. Eyelid and glands keep the eye tree from dust. The lens is large and rounded. It is present in the back of cornea. A fold of epithelium called the iris surrounds the lens. The iris can dilate or constrict and control the size of the pupil.

Accommodation of eye

The bending (refracting) of light rays at a focal point on the retina is called focusing or accommodation. Light waves moves from air into the cornea. These waves are refracted due to change in density between the two media. The lens increase refraction. The eye of amphibian can focus on distant objects at rest. But the protractor lentis muscle move the lens forward for focusing near objects. Receptors called rods and cones are present in the retina. Cones detect co lours. Thus amphibians can distinguish between some wavelengths of light with the help of cones. Amphibians have complex neuronal interconnections in the retina. Therefore, amphibian can distinguish between flying insect prey, shadow of predator and background movements.

The auditory system of amphibians is adapted for life on land. It transmits both substrate borne vibrations and airborne vibrations. The ears of anurans consist of a tympanic membrane, a middle ear and an inner car. :

(i) Tympanic membrane: The tympanic membrane is a piece of integument. It stretches over a cartilaginous ring. This ring receives airborne vibrations. It transmits vibrations to the middle ear.

(ii) Middle ear: It is a chamber beneath the tympanic membrane. A bone of middle ear called the stapes (columella) touch the tympanic membrane. Stapes transmits the vibrations of the tympanic membrane into the inner ear. Ear receives two types of vibrations:

(a) High- frequency (1,000 to 5,000 Hz): These are air borne vibrations. These are transmitted to the inner ear though tympanic membrane.

(b) Low-frequency (100 to 1,000 Hz): These are substrate borne vibrations. These are transmitted through the front appendages and the pectoral girdle. These waves finally enter into the inner ear through operculum.

Control of sound frequency: The anuran can lock operculum and stapes with the help of muscles. Thus they can screen out high or low-frequency sounds. The anurans use low and high frequency sounds in different situations. For example, mating calls are higt-frequency sounds. Thus it is used only during breeding season. The low-frequency sounds are used for warning ofpredators.

Ear in salamander: Salamanders lack a tympanic membrane and middle ear. They live in streams, ponds, caves, and beneath leaf litter. They have no mating calls. They hear only low-frequency vibrations. These vibrations are transmitted through the substrate and skull to the stapes and inner ear.

Equilibrium: The inner ear of amphibians has semicircular canals. These canals detect rotational movements.

EXCRETION AND OSMOREGULATION

The kidneys of amphibians are present on the sides attached to the dorsal wall of the body cavity. A duct opens in cloaca. The cloaca has ventral outgrowth called urinary bladder. Urinary bladder stores urine. There are following adaptations in the amphibians for excretions:

1. Aquatic amphibians: The nitrogenous wastes of amphibians are ammonia or urea. The freshwater amphibians excrete ammonia. It is the immediate end product of protein metabolism. Therefore, they do not spend energy on converting ammonia into other compound. The ammonia diffuses into the surrounding water. Therefore, it does not produced toxic effect.

2. Terrestrial amphibians: Amphibians that spend more time on land excrete urea. Urea is produced from ammonia in liver. Urea is less toxic than ammonia. But it still requires large quantities of water for its excretion. Urea can be stored in the urinary bladder. Some amphibians excrete ammonia in water and urea on land.

Osmoregulation

Osmoregulation is a biggest problem of the amphibians. They must remove excess water and conserve essential ions. Amphibian kidneys produce large quantities of hypotonic urine. Their skin and walls of the urinary bladder transport Na, Cl and other ions into the blood.

The amphibians conserve water on land. Adult amphibians do not drink water. Their skin is also not impermeable like other tetrapods. Their kidneys are unable to produce hypertonic urine. Instead, amphibians loss water by their behavior. They show following type of behaviours:

1. Nocturnal amphibians: They do not come out in desiccating conditions. Many terrestrial amphibians are nocturnal. The go to high humidity area during day times. These areas are present under stones, in logs , leaf mulch or burrows. They come out at night and absorb the lost water through skin.

2. Diurnal amphibians: They live in areas of high humidity. They rehydrate themselves by entering the water.

3. Reduction in surface area: Many amphibians reduce exposed surface area of body to air. It reduces loss of water by evaporation. They curl their bodies and tails into tight coils. They bring their limbs close to their bodies. Many individuals come close to each other in groups. It reduces overall surface area.

4. Protective covering: Some amphibians have protective coverings. It reduces the water loss. Their skin has some hardened regions. These regions are resistant to water loss. They close the mouth of burrows with these hardened regions of skin. It maintains high humidity in the burrow.

5. Cocoon formation: Some amphibians form cocoons. It covers the body during long periods of dormancy and reduces the loss of water. Cocoons are made from outer rs of the skin. This layer of skin detaches and become parchment like. These cocoons open only at the flares or the mouth. Cocoon can reduce water loss by 20 to 50%.

6. Rehydration: The skin is also most important structure for rehydration. The amphibian flattens its body on moist surfaces. It absorbs water. The permeability, vascularization, and epidermal layering of skin promote water reabsorption. Minute channels increase surface area. These areas spread water over surfaces which are not directly exposed to water.

7. Storage of water: Amphibians can also temporarily store water. Water is stored in urinary bladder and lymph sacs. This water is absorbed to replace the loss of water by evaporation. Amphibians living in very dry environments can store water equal to 35% of their total body weight.

REPRODUCTION, DEVELOPMENT, AND METAMORPHOSIS

Amphibians are dioeeious. Their ovaries and testes are located near the dorsal body wall. Fertilization is external. The developing eggs lack any resistant coverings. Therefore, development takes place in moist habitats in water. A few anurans have terrestrial nests.

These nests are covered with foam. This foam reduces the loss of water. Sometimes these nests are placed near water. In a few species, larval stages are passed in the egg membranes. The immatures hatch into an adult like body.

Fertilization and development

External fertilization is less common in salamanders. Only 10% salamanders have external fertilization. Remaining salamanders develop spermatophores and fertilization is internal. Eggs are deposited in soil or water. Or they may be retained in the oviduct during development.

All caecilians have internal fertilization. 75% caecilians have internal development. Tadpole larvae are formed during development of amphibians. Amphibian tadpole larva is different from the adults. It has different mode of respiration, form of locomotion and diet. These differences reduce competition between adults and larvae.

Breeding behaviour

Amphibian: Internal factors like hormones and external factors determine the timing of reproductive activities. Temperature is most important environmental factor in temperate region. It induces physiological changes in the amphibians. These changes control the breeding and breeding periods. Breeding occurs in spring and summer. In tropical regions, rainy seasons induce breeding in amphibians. The individuals locate breeding sites and identify potential mates by courtship behavior. It also prepares the individuals for reproduction. It also ensures that eggs are fertilized and deposited at proper locations.

Salamander: Salamanders use olfactory and visual signs for courtship and mating. The anurans use male vocalizations and tactile signs. Many species congregate in one location during breeding activity. Male vocalizations are species specific. These are used for initial attraction and contact between mates. Then tactile cues become more important. The male mounts on the female. The male grasps the female with the help of his forelimbs around her waist. The male is dorsal to the female. This positioning is called amplexus. It lasts from I to 24 hours. The male releases sperm and the female releases eggs during amplexus.

Caecilian: Little is known about the breeding behavior in caecilian. Males have an intermittent organ (copulatory organ). It is a modification of the cloaca! wall. Therefore, fertilization is internal.

Vocalization

Sound production has reproductive function in male anurans. Frogs produces different calls:
1. Advertisement calls:
It is used to attract females to breeding areas. It is also an announcement for other males the given territory is occupied. Advertisement calls are species specific. These calls induce psychological and physiological changes in female. As a result the female get ready to breed.

2. Receptive calls: If female get ready for breeding then it produces receptive calls.

3. Release call: Release call informs the partner that it is incapable of reproducing. Some male try in amplexus unresponsive females. Such females also give release calls. Sometimes, a male mistakenly identified other male as female. Thus otlit r male also produce release call.

4. Distress calls: These calls are not associated with reproduction. These calls are produced in response to pain or danger of a predator. The calls are much aloud. It frightens the predator to release the frog. The distress call of the South American jungle frog is as loud as a cat in distress.

Sound producing apparatus

The sound production apparatus of frogs consists of the larynx and its vocal cords. It is called laryngeal apparatus. It is well developed in males. They possess a vocal sac. Vocal sac is a diverticulum from the lining of the buccal cavity. Lungs force air in vocal cords and cartilages of the larynx. This air produces vibrations in them. Muscles control the tension of the vocal cords and regulate the frequency of sound. Vocal sacs act as resonating structures. They increase the volume of the sound.

Advantages of vocalization

1. The amphibians live in widely dispersed habitats. Therefore, it is useful for them to attract mates from distant places.

2. Many species of frogs collected at the same pond for breeding. It becomes difficult for them to find their proper mate. Vocalizations help to attract their mate of same species.

Parental Care

Parental care increases the chance of development of an egg. But it requires large amount of amount from the parents. Mostly both parents care for the egg clutches. It is most common form of parental care in amphibians. It may be:

1. Maternal care: It takes place in species with internal fertilization, e.g. salamanders an caecilians.

2. Parernal care: It takes place in species with external fertilization, e.g. anurans. It involves aeration of aquatic eggs, cleaning and moistening of terrestrial eggs, protection of eggs from predators, or removal of dead and infected eggs.

Eggs re transported during development on land. Females of the genus Pipa carry eggs on their backs. Two species of Rheobatrachus were discovered in Australia. Rheobatrachus females brooded tadpoles in their stomachs. The young come out through mouths the female. But it is not known whether the female swallow egg or tadpole larvae. The stomachs of female expanded and till most of her body cavity during brooding. Thus the stomach stops producing digestive secretions. Viviparity and ovoviviparity occur in salamanders and caecilians.

Metamorphosis

Metamorphosis is a series of structural, physiological, and behavioral changes that transform a larva into an adult. A number of environmental conditions influence the time required for metamorphosis. These conditions are collections and availability of food. Metamorphosis is directly controlled of neurosecretions of hypothalamus, hormones of the anterior lobe of the pituitary gland and the thyroid gland.

1. Minor morphological changes take place during metamorphosis of caecilians and slamanders. Reproductive structures develop, gills are lost, and a caudal fin is lost.

2. Major changes take place during metamorphosis of tadpole into the small frog in the anuran. Limbs and lungs are developed. The tail is reabsorbed and the skin thickens.

Many changes take place in the head and digestive tract.

Paedomorphosis

A phenomenon in which larva becomes sexually mature while still showing larval characteristics is called paedomorphosis. The mechanism of metamorphosis explains paedomorphosis in amphibians. Paedomorphosis mostly takes place in some families of salamander. In other families, the occurrence of paedomorphosis is variable. It is influenced by environmental conditions. Two conditions promote paedomorphosis:

1. Some salamanders do not respond to thyroid hormones. Therefore, it becomes paedomorphic.

2. Some larvae do not produce the hormone necessary tbr metamorphosis. Therefore, they become paedomorphic.


5 Marks Questions

Chapter 13
Organisms and Populations

5 Marks Questions
1. What is altitude sickness? What its causes and symptoms? How does human body try to overcome altitude sickness?
Ans. Breathlessness at high attitudes.Cause :Low atmospheric pressure at high altitudes due to which body does not get enough oxygen. Symptoms :Nausea, fatigue and heart palpitations.
Body adapts by :
(a) increasing red blood cell production
(b) decreasing binding affinity of haemoglobin
(c) by increasing breathing

2. Orchid flower, Ophrys co-evolves to maintain resembelance of its petal to female bee. Explain how and why does it do so?
Ans.

  • employs ‘Sexual deceit’
  • one petal bears uncanny resemblance to female of the bee.
  • Male bee is attracted to what it perceives as a female ‘pseudocopulates,’during which pollen dusted on male been is body .
  • Male bee transfers pollen to another flower when the same bee pseudocopulates with another flower.
  • Ophrysdoes so because pollination success will be reduced unless it co-evolves with female bee.

3.Describe the exponential growth model of a diagram along with a curve?
Ans. This kind of curve is observed in the case of under population of reindeer growing in apredator free natural environment having plenty of food. In this case, the curve formed is J-curvethe small population first takes time to adjust into new environment so there is no increase in thepopulation. Once they get adapted they multiply exponentially. This growth & multiplicationcontinues so far the food is available. After sometime the food supply becomes less as compared tothe population increases. This causes mass starvation & mortality & results in the formation of Jshaped curve.
The J-shaped growth form is described by equation
Δ N Δ t = rN or Δ N Δ t N ΔNΔt= rN or ΔNΔtN

4.Describe the logistic growth model of population along with a suitable curve. Why is this curve more realistic?
Ans. The logistic growth curve shows a sigmoid or a S-shaped curve. It has three phases:-
(i) Lag-phase :- It is the early phase of little or no growth. Lag phase is one in which under population of cells adapt to or stablises with the growth conditions before embarking up their multiplication.
(ii) Log phase or Exponential phase :- It is the middle phase of rapid or geometric rise, Once stabilized cells starts to multiply rapidly when the small population is stablised, the multiply becomes faster because of the plenty amount of food & other requirements of life.
(iii) Stationary phase or steady phase:- Soon after the amount of food decreases in proportion to the number of cells & this results in the onset of stationary phase. During this phase, the number of new cells produced is roughly equal to the number of cells dead & so there is no net increase in the number of cells.
Sigmoid growth curve is demonstrated by fo Δ N Δ t = rN ( K − N ) N ΔNΔt = rN (K−N)N

Δ N − rate of change inpopulation ΔN− rate of change inpopulation Δ t – change in time . Δt – change in time.
K – carrying capacity
R – biotic potential

5.Give an example to show that completely unrelated species can also compete for same resources?
Ans. Completely unrelated species can also compete for same resources for e.g. In certain shallow lakes of South America the visiting flamingoes & the native fishes compete for the same zooplanktons as their food.

6.What is Age pyramid? What are the different types of age pyramid?
Ans. The geometrical diagrammatic representation of different age groups in a population of any organism is called Age of pyramids. These are of three types:-
i) Expanding pyramid:- It is a broad base, triangular pyramid which represents a population containing large number of young people. It is rapidly expanding population with high birth rate.
ii) Stable pyramid:- It represents a moderate proportion of young to old. As the rate of growth becomes slow & stable i.e.- pre-reproductive & reproductive age groups becomes more or less equal in size.
iii) Declining Pyramid:- The type of pyramid of population decreasing in size is characterised by a narrow base because there are fewer pre-reproductive individuals than in the other two age categories.

7. Differentiate between regulators & conformers? Why do small animals do not show regulations?
Ans. The organisms which maintain homeostasis by physiological or behavioral means & ensures aconstant body temperature & constant osmotic concentration etc. are called regulators e.g. all birds,mammals some lower vertebrates & invertebrates, for example in summer, when outside temp is morethan our body temperature we sweat profusely evaporative cooling brings the body temp – down.Whereas those organisms which cannot maintain a constant internal environment. Their bodytemperature changes with ambient temperature e.g. majority of animals & nearly all plants.

Small organisms does not show regulationbecause thermoregulation is an energy –expensive process. Since small animals havelarge surface area relative to volume, they tendto lose body heat very fast when it is coldoutside they have to expend much energy togenerate body heat through metabolism.


Watch the video: Reproduction and development in Amphibians. Vocalizations, parental care and metamorphosis (January 2022).