How long can a unicellular organism live without nutrition? What happens after that? Does it depend on the domain?

Say I have three unicellular organisms: a eukariote, a bacterium and an archaeon. If I cut off nutrition from them at the same time, how long will it take for them to die? What will their death look like, and do they actually need to die? If so, why?

This is very dependent on the organism within each of the groups you mention. While for the most part, archea are the extremophiles and have the ability to withstand many extreme conditions, nutrient limitation survival greatly varies. I think you could easily find organisms in each group that could withstand nutrient limitation well.

A good example would be yeast, which is a single celled organism you may have actually worked with. If you take laboratory yeast, in their diploid state, and starve them, they will undergo meiosis, and in their spore form, live for a very very long time without nutrients, protected by their ascus (which is actual their dead mother cell).

Yeast can also completely desiccate and still live. When you pick up an active yeast packet for baking, those yeast have not only been starved, but have been completely sucked dry of their water. Yet when you add water back, they live (though a great number of them will die).

I think in general, most single celled organisms have a certain tolerance for low nutrient conditions. This does happen to them a lot. All it means is they slow their cell cycle down, stop dividing, and just undergo a caution period. There is all sorts of signaling in the cells that sense the nutrients, and slow growth based on their conditions.

Unicellular Organisms

Essentially, unicellular organisms are living organisms that exist as single cells. Examples include such bacteria as Salmonella and protozoa like Entamoeba coli. Being single celled organisms, various types possess different structures and characteristics that allow them to survive.

According to a report that was released in 2012 from the University of Potsdam in German, it was stated that the ocean is home to an estimated 2.9×10^29 unicellular organisms (about 20,000 species).

Here, it's worth noting that this figure only represents the number of single-celled organisms in the ocean and not on land, which in other words means that the total number is much higher.

Although there are a vast number that exist on earth, they are divided into the following groups:

  • Bacteria
  • Protozoa
  • Fungi (unicellular)
  • Algae (unicellular)
  • Archaea

Despite their diversity, they share a number of basic characteristics.

They are alive and share a number of characteristic with all living things such as:

Organization - Unicellular organisms possess various structures that make it possible for them to survive. These structures are contained within the cell (in the cytoplasm) and include such structures as the endoplasmic reticulum and genetic material among others.

Growth - Given that they are living things, unicellular organisms increase in size.

Reproduction - Unicellular organisms also reproduce, which allows them to form other organisms that are like themselves. The genetic material possessed by these microorganisms divides allowing each of the daughter cells to get an exact copy of the genetic material that was contained in the original cell.

Response to external environment - Unicellular organisms also respond to various conditions such as change in temperature, light as well as touch. It's this ability to respond to environmental changes that make it possible for unicellular organisms to find food and continue surviving.

* Considering that single-celled (unicellular) organisms have the characteristics of living things, we cannot include viruses here. This is due to the fact that viruses are not considered living things despite the fact that they have genetic material and various characteristics of living organisms.

There are a number of characteristics that distinguish viruses from other unicellular organisms, these include:

  • Viruses do not grow/increase in size once they are formed
  • Viruses don't take in energy like other unicellular organisms.
  • They depend on the host cell to reproduce (they are unable to reproduce on their own).

The Cells in Your Body

This resource provides you with an introduction to cells.

Everyone&rsquos body is made of the same basic stuff. All living things, large or small, plant or animal, are made up of cells. Most living things are made up of one cell and they are called unicellular organisms. Many other living things are made up of a large number of cells that form a larger plant or animal. These living things are known as multicellular organisms. Water makes up about two thirds of the weight of cells.

Cells are very small most cells can only be seen through a microscope. Cells are the smallest living units that are capable of reproducing themselves. Each cell in your body was made from an already existing cell. All plants and animals are made up of cells. In this article, we will talk about the cells that make up You.

All the parts of your body are made up of cells. There is no such thing as a typical cell. Your body has many different kinds of cells. Though they might look different under a microscope, most cells have chemical and structural features in common. In humans, there are about 200 different types of cells, and within these cells there are about 20 different types of structures or organelles.

All cells have a membrane. Cell membranes are the outer layers that hold the cell together. They let nutrients pass into the cell and waste products pass out. Not everything can pass through a cell membrane. What gets through and what doesn&rsquot depends on both the size of the particle trying to get in and the size of the opening in the membrane.

Cells also have a nucleus. This is the cell&rsquos control center. Cells continually divide to make more cells for growth and repair in your body. The nucleus contains the information that allows cells to reproduce, or make more cells. Another important part of a cell is the mitochondrion. This is the part of the cell where food and oxygen combine to make energy.

You know that you need air to breathe. It is the oxygen in air that your body really needs. Every cell in your body needs oxygen to help it metabolize (burn) the nutrients released from food for energy. You also know that you need food. Food gives you energy, but oxygen is needed to break down the food into pieces that are small enough for your cells to use This is known as cellular respiration and it is the process of oxidizing food molecules, like glucose, to carbon dioxide and water. The energy released is chemically trapped for use by all the energy-consuming activities of the cell. Your cells are the energy converters for your body.

Different cells have different jobs to do. Each cell has a size and shape that is suited to its job. Cells that do the same job combine together to form body tissue, such as muscle, skin, or bone tissue. Groups of different types of cells make up the organs in your body, such as your heart, liver, or lungs. Each organ has its own job to do, but all organs work together to maintain your body. A group of different organs working together to do a job makes up a system. All the systems in your body are like members of a team whose job it is to keep you alive and healthy.

The different types of cells in your body have different, specialized jobs to do. The specialization of cells depends almost always on the exaggeration of properties common to cells. For example, cells that line the intestine have extended cell membranes. This increases the amount of surface area that is available to absorb food. Nerve cells can be very long, which makes them efficient in sending signals from the brain to the rest of your body. Cells in heart muscle process a lot of energy, so they have a large number of mitochondrion, the part of the cells where energy is made.

Like all living things, cells die. The number of cells that an adult male loses per minute is roughly 96 million. Fortunately, in that same minute, about 96 million cells divided, replacing those that died. Just as you shed dead skin cells, dead cells from internal organs pass through and out of the body with waste products. The length of a cell&rsquos life can vary. For example, white blood cells live for about thirteen days, cells in the top layer of your skin live about 30 days, red blood cells live for about 120 days, and liver cells live about 18 months.

NCERT Exemplar Solutions for Class 10 Science Chapter 6 Life Processes

These Solutions are part of NCERT Exemplar Solutions for Class 10 Science. Here we have given NCERT Exemplar Solutions for Class 10 Science Chapter 6 Life Processes

NCERT Exemplar Solutions for Class 10 Science Chapter 6 Short Answer Questions

Question 1.
Name the following :

    1. The process in plants that links light energy with chemical energy.
    1. Organisms that can prepare their own food.
    2. Cells that surround a stomatal pore.
    3. The cell organelle where photosynthesis occurs.
    4. Organisms that cannot prepare their own food.
    5. An enzyme secreted by gastric glands in stomach that acts on proteins.
    1. Photosynthesis
    2. Autotrophs
    3. Guard cells
    4. Chloroplast
    5. Heterotrophs
    6. Pepsin.

    More Resources

    Question 2.
    “All plants give out oxygen during day and carbon dioxide during night.” Do you agree with the statement ? Give reason.
    (CCE 2010)
    Yes. Respiration is going on throughout day and night. Photosynthesis occurs only during the day. Rate of photosynthesis is several times the rate of respiration. All the CO2 produced in respiration is also consumed in photosynthesis during the day time. Therefore, during day time, plants give out oxygen, which is a product of photosynthesis. However, during night when there is no photosynthesis, plants liberate carbon dioxide.

    Question 3.
    How do the guard cells regulate opening and closing of stomatal pores ? (CCE 2010, 2012)
    Opening and closing of stomata is regulated by gain or loss of turgidity of their guard cells. During opening of stomata, guard cells withdraw K + ions from surrounding epidermal cells, followed by absorption of water from them. As a result, guard cells swell up and become turgid. Their outer thin and elastic walls bend outwardly followed by outward movement of thicker inner walls. The latter creates a pore in between the two guard cells.
    During closure movement of stomata, guard cells send out K + ions. Water also passes out. Guard cells become flaccid. Their inner thick walls come to touch each other. The stomatal pore gets closed.

    Question 4.
    Two green plants are kept separately in oxygen free containers, one in dark and the other in continuous light. Which one will live longer ? Give reasons. (CCE 2010)
    Plant kept in continuous light will live longer due to

    1. Manufacture of food and hence its availability to the plant for maintenance and growth,
    2. Production of oxygen in photosynthesis and its availability for respiration of the plant. Plant kept in oxygen free container kept in dark will die within a few days due to non-availability of food and oxygen.

    Question 5.
    If a plant is releasing carbon dioxide and taking in oxygen during the day, does it mean that there is no photosynthesis occurring ? Justify your answer.
    A plant releases carbon dioxide and takes in oxygen only when photosynthesis is either absent or too small as not to compensate for respiration.
    (In photosynthesis, plants absorb CO2 and release O2. The normal rate of photosynthesis is many times the rate of respiration. As a result, CO2 produced during respiration is consumed and a lot of more is absorbed from outside. Oxygen produced during photosynthesis is much more than required for respiration. Therefore, oxygen passes out.)

    Question 6.
    Why do fishes die when taken out of water ?
    Fish taken out of water die due to

    1. Inability to obtain oxygen from air
    2. Collapsing of gill lamellae so that no space is left for gaseous exchange.

    Question 7.
    Differentiate between an autotroph and a heterotroph.

    Autotroph Heterotroph
    1. Food: It manufactures its own food. It obtains its food from outside sources.
    2. Chlorophyll: It has chlorophyll for performing photosynthesis. Chlorophyll is absent.
    3. Energy: It is obtained from sunlight and changed into chemical energy. It does not require an external source of energy as the same is present in food obtained from outside.
    4. Digestion: It is absent. Food obtained from outside is digested before being absorbed and assimilated.

    Question 8.
    Is nutrition a necessity for an organism ? Discuss.
    Yes, nutrition is a must for an organism because of the following reasons :
    Importance of Nutrition/Food

    1. Food provides energy: Energy is required by the body all the time, whether asleep, taking rest or doing work. When the body is not doing any apparent work, energy is still being consumed in maintaining order. Further, biosynthetic activities continue for replacing materials being consumed or degraded. A number of other activities are going on all the time. Heart is always beating. Breathing movements never stop. Food eaten by a person has to be digested and absorbed. Excretory products are being produced.
    2. Body Structure: All body components are built up of materials obtained from food.
    3. Food is used in building protoplasm. More protoplasm is required for formation and enlargement of cells that take part in growth of the organism.
    4. Food provides materials for replacement and repair of worn out or damaged structures.
    5. Hormones and enzymes are formed from ingredients of food. They regulate metabolism and body functions. ‘
    6. Defence system of the body is formed from raw materials got- from food.
    7. Food provides materials to form reproductive structures.

    Question 9.
    What would happen if green plants disappear from earth ?
    Herbivores will die of starvation followed by carnivores and then decomposers.

    Question 10.
    Leaves of a healthy plant were coated with vaseline. Will this plant remain healthy for long ? Give reasons for your answer.
    The plant will not remain healthy for long. Vaseline covers the cuticle and blocks the stomata. As a result

    1. It is unable to obtain oxygen from air for respiration,
    2. It is unable to perform photosynthesis as no carbon dioxide diffuses from air.
    3. In the absence of transpiration, the leaves get heated up and injured.

    Question 11.
    How does aerobic respiration differ from anaerobic respiration ?

    Aerobic Respiration Anaerobic Respiration
    1. Method: It is the common method of respiration. It occurs permanently only in a few organisms. In others it may occur as a temporary measure to overcome shortage of oxygen.
    2. Steps: It is completed in 3 steps—glycolysis, Krebs cycle and terminal oxidation. There are two steps— glycolysis and anaerobic breakdown of pyruvic acid.
    3. Oxygen: It requires oxygen. Oxygen is not required.

    Question 12.
    Match the words of column A with those of column B

    a — ii,
    b — i,
    c —iv,
    d —iii.

    Question 13.
    Differentiate between an artery and a vein. (CCE 2013)

    Artery Vein
    1. Direction of Flow: It carries blood from heart to an organ. It brings blood from an organ towards the heart.
    2. Speed: Blood flow is rapid in artery. Blood flow is slow in vein.
    3. Jerks: Blood flows with jerks. Blood flows smoothly.
    4. Pressure: Blood flows under pressure There is little pressure.
    5. Internal Valves: They are absent. Internal valves are present to prevent back flow.
    6. Wall: It is thick and elastic. It is comparatively thinner and little elastic.
    7. Lumen: Narrow. Wide.
    8. Type of Blood: Artery carries oxygenated blood except pulmonary arteries. Vein carries deoxygenated blood except pulmonary veins.
    9. Occurrence: It is deep seated. It is superficial.
    10. Collapsibility: Artery is not collapsible. Vein is collapsible.
    11. Blood After Death: It does not contain blood after death. Vein is full of blood even after death.

    Question 14.
    What are the adaptations of leaf for photosynthesis ?

    1. Large Surface Area : Leaf has a large surface area to absorb maximum amount of lift.
    2. Leaf Orientation: It is such as to absorb the optimum amount of light.
    3. Veins: A number of veins occur in a leaf. They provide mechanical strength to the otherwise soft leaf. Veins also take part in quick transport of substances to and from the mesophyll cells.
    4. Transpiration: Leaf is the seat of transpiration. Transpiration cools the surface of leaf for optimum photosynthesis.
    5. Gaseous Exchange: A leaf has a large number of stomata for gaseous exchange, required for photosynthesis.
    6. Chloroplasts: A very large number of chloroplasts occur in the mesophyll of a leaf for efficient photosynthesis.

    Question 15.
    Why is small intestine in herbivore longer than in carnivores ? (CCE 2013)
    Herbivorous diet has a large bulk. It is rich in cellulose. However, cellulose digesting enzymes are absent in them. For digestion
    of cellulose, herbivores depend upon bacteria. The food has to be kept for longer period in the intestine for complete digestion of cellulose. Therefore, small intestine where bacterial digestion of cellulose occurs has to be long. There is no such requirement in carnivores as their diet has a smaller bulk which does not contain cellulose. They have a shorter intestine.

    Question 16.
    What will happen if mucus is not secreted by gastric glands ?
    Mucus protects the stomach from corrosion by HCl and pepsin of gastric juice. In the absence of mucus, the lining layer of stomach wall will be corroded forming gastric ulcers. There will be excessive acidity and extreme discomfort.

    Question 17.
    What is the significance of emulsification of fats ?
    Emulsification of fat is the conversion of large fat pieces into very fine fat globules which can be efficiently acted upon by lipase.

    Question 18.
    What causes movement of food inside the alimentary canal ?
    Involuntary movement consisting of rhythmic contraction and expansion of the alimentary canal called peristalsis.

    Question 19.
    Why does absorption of digested food occur mainly in the small intestine ?

    1. Digestion of food is completed only in small intestine.
    2. Wall of the intestine bears a number of finger-like projections called villi. Villi provide a large surface area to the lining layer for absorption.
    3. The epithelium, lining the villi, is made of cells having a number of very fine projections known as microvilli. Microvilli are specialised for absorption.
    4. Wall of the intestine, especially the interior of villi, has lymph and blood vessels for carrying the absorbed food to different parts of the body.

    Question 20.
    Match the articles of columns A and B :

    (b) Heterotrophic nutrition

    (d) Digestion in food vacuoles

    a — iv,
    b — iii,
    d — ii.

    Question 21.
    Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms ? (CCE 2011, 2012)
    Most of the aquatic organisms obtain oxygen from water. The amount of dissolved oxygen is quite small as compared to the amount of oxygen in air. Therefore, in order to obtain required oxygen from water, the aquatic animals like fishes have to breathe much faster as compared to the terrestrial organisms.

    Question 22.
    Why is blood circulation in human heart called double circulation ? (CCE 2011)
    Blood circulation in human heart is called double circulation as blood passes twice through the heart in order to complete one cycle—once through right side as deoxygenated blood and once through left side as oxygenated blood. Deoxygenated blood passes to lungs. It returns to left side as oxygenated blood. Oxygenated blood is supplied to different parts of the body. It returns to right side of the heart as deoxygenated blood.

    Question 23.
    What is the advantage of having four chambered heart ? (CCE 2010)
    Four chambered heart ensures complete separation of oxygenated and deoxygenated bloods. Only oxygenated blood is pumped out to supply all parts of the body. It is received by left auricle from lungs and pumped out by left ventricle. The blood returns to heart after deoxygenation. It is received by right auricle and pumped out by right ventricle to lungs for oxygenation. The mechanism is useful to animals with high energy needs (due to thermoregulation and higher activity) such as birds mammals.

    Question 24.
    Mention the major events during photosynthesis. (CCE 2011, 2012)

    1. Photolysis: With the help of light energy, oxygen evolving Z-complex splits up water into its components —- protons (H + ), electrons (e – ) and oxygen.
    2. Absorption of Light Energy: Chlorophyll absorbs light energy.
    3. Primary Reaction: Chlorophyll converts the absorbed light energy into chemical energy. It is called primary reaction of photosynthesis. It builds up ATP with the help of excited electrons.
    4. Formation of Reducing Power: Coenzyme NADP + is changed to reduced form of NADPH.
    5. Reduction of CO2: Carbon dioxide is reduced enzymatically with the help of NADPH and ATP to form carbohydrates.

    Question 25.
    In each of the following situations, what happens to the rate of photosynthesis ?
    (a) Cloudy days
    (b) No rainfall in the area
    (c) Good manuring
    (d) Stomata get blocked due to dirt.
    (a) Cloudy Days: Photosynthesis is reduced due to low light intensity.
    (b) No Rainfall: Rate of photosynthesis decreases due to wilting of leaves, closure of stomata and reduced availability of hydration.
    (c) Good Manuring: Rate of photosynthesis increases as good manuring increases soil fertility by providing more minerals, moisture and aeration.
    (d) Blocked Stomata: It decreases the rate of photosynthesis by reducing gaseous exchange and non-cooling of leaves due to reduced transpiration.

    Question 26.
    Name the energy currency in the living organisms. When and where is it produced ?
    Energy Currency. ATP (adenosine triphosphate) is the energy currency of the living beings.
    It is produced both during respiration (in all organisms) and photosynthesis (in plants only).

    Question 27.
    What is common amongst Cuscuta, Ticks and Leeches ?
    All are parasites which obtain their nutrition from their hosts direcdy without killing them.

    Question 28.
    Explain the role of mouth cavity in digestion of food.

    1. Moistening of food with saliva,
    2. Tongue helps in thorough mixing of food with saliva.
    3. Crushing of food into smaller pieces by teeth,
    4. Partial digestion of starch by enzyme amylase contained in saliva,
    5. Rolling of crushed, moistened and partially digested food into small ball or bolus by the tongue.

    Question 29.
    What are the functions of gastric glands present in the wall of stomach ? (CCE 2011)
    Gastric glands produce the following substances :

    1. Mucus: Moistening the food and protecting the wall of the stomach from corroding action of HCl and pepsin.
    2. HCl: It makes the food soft, sterilised and acidified for pepsin to act upon food.
    3. Gastric Lipase: It is active only in infants. It partially breaks down fat into its components.
    4. Rennin: It is active in infants where it helps in curdling of milk (casein to paracasein) for action of pepsin.
    5. Pepsin: It is secreted in inactive state of pepsinogen. Pepsin hydrolyses proteins into soluble fragments of peptones and proteoses.

    Question 30.
    Match the items of columns A and B

    a — i,
    b — iv,
    c — ii,
    d — iii.

    Question 31.
    Name the correct substrates for the following enzymes :
    (a) Trypsin
    (b) Amylase
    (c) Pepsin
    (d) Lipase.
    (a) Trypsin: Proteins, peptones and proteoses,
    (b) Amylase: Starch, dextrins.
    (c) Pepsin: Proteins.
    (d) Lipase: Fats.

    Question 32.
    Why do veins have thin walls as compared to arteries ?
    In arteries, blood flows under pressure so that their walls are thick and elastic. In veins the blood is Therefore, their walls are thin. Rather, they possess semilunar valves to check back flow of blood.

    Question 33.
    What will happen if platelets were absent in the blood ?
    Blood platelets are a source of thromboplastin which is essential for blood clotting at the place of injury. In the absence of blood platelets, blood clotting will be litde resulting in greater loss of blood from the place of injury.

    Question 34.
    Plants have low energy needs as compared to animals. Explain.
    Plants are anchored. They do not move about. Most of their body is made of dead cells and cell walls. Therefore, their requirement for energy is quite low as compared to animals which move about fast in search of food, mate and shelter.

    Question 35.
    Why and how does water enter continuously into root xylem ?
    Root cells in the absorbing part of root pick up ions actively from soil. Ions pass inwardly increasing osmotic concentration of xylem. Because of it soil water (which has very low osmotic concentration) continuously passes into root xylem.

    Question 36.
    Why is transpiration important for plants ?

    1. Cooling: Evaporation of water from the aerial parts results in lowering of their temperature which will otherwise rise due to exposure to sun.
    2. Concentration of Minerals: Transpiration helps in increasing concentration of minerals present in rising water.
    3. Transport: It creates a pull that helps in transport of water and minerals.

    Question 37.
    How does leaves of plants help in excretion ? (CCE 2016)
    Waste materials produced in plant cells are stored ’in their vacuoles. In leaves, the waste materials are

    1. Stored in vacuoles of mesophyll and epidermal cells,
    2. Oxalic acid is crystallised as calcium oxalate.
    3. Nitrogenous wastes are changed into alkaloids
    4. Vaste aromatic compounds are changed into tannins. As the old leaves fall, the waste materials are also removed from the plant.

    NCERT Exemplar Solutions for Class 10 Science Chapter 6 Long Answer Questions

    Question 38.
    Explain the process of nutrition in Amoeba.

    1. Ingestion: (L. ingestus — taken in). It is taking in of solid food with the help of temporary or permanent mouth. Amoeba can ingest food particles from any point on its surface. Paramoecium (another unicellular organism) has fixed point for the same. Amoeba captures food with the help of temporary finger-like processes called pseudopodia. Paramoecium has small hair-like processes called cilia. Beating of cilia creates current in water that pushes food particle through cytostome or cell mouth. The process of ingestion of solid food particle by a cell or unicellular organism is called phagocytosis.
      As soon as Amoeba comes in contact with a food particle or prey, it throws pseudopodia all around the same. The tips of encircling pseudopodia fuse and the prey comes to lie in a vesicle or phagosome.
    2. Digestion: It is conversion of complex insoluble food ingredients into simple absorbable form. Digestion can be intracellular or intercellular. Intercellular digestion occurs in a digestive tract. Intracellular digestion takes place in the cytoplasm of cells. Here, a lysosome fuses with phagosome to produce a food vacuole, also called gastriole or temporary stomach. Reaction of food vacuole is acidic at first and alkaline later on. Digestion of food occurs with the help of digestive enzymes brought by lysosome. It changes complex insoluble substances of food into simpler absorbable substances.
    3. Absorption: The digested simple and soluble substances pass out of food vacuole into the surrounding cytoplasm.
    4. The absorbed food materials are converted into various constituents of protoplasm including food reserve.
    5. (L. egestus — discharge): It is throwing of undigested components of food out of the body. In Amoeba, the old food vacuole with heavier undigested material reaches the rear end, passes to the surface, fuses with surface membrane and throws out the undigested materials. The process is called egestion. Paramoecium has a definite cytopyge or cell anus.

    Question 39.
    Describe the alimentary canal of man.
    Alimentary canal (L. alere-to nourish) is a tubular passage extending from mouth to anus through which food passes during its digestion and absorption. It is about 9 metres in length. Alimentary canal consists of mouth, buccal cavity, oesophagus, stomach, small intestine, large intestine and anus.

    1. Mouth: It is a transverse slit like aperture that occurs in between the nose and the chin. Mouth is bounded by two soft, movable sensitive lips, upper and lower. Lips help in holding the food. They also aid in phonation (speech).
    2. Buccal or Oral Cavity (L. bucca-cheek): It is anterior part of alimentary canal that extends from mouth to pharynx and lies between two jaws, upper (fixed) and lower (movable). It has palate on upper side, throat and tongue on the lower side and cheeks on the lateral sides. Both the jaws contain teeth in semicircular rows or arches.
      1. It is a muscular, sensory, movable and protrusible flat structure which is attached posteriorly over the lower jaw. Tongue bears taste buds for tasting the quality of food—sweet anteriorly, salt anterio-laterally, sour postero-laterally and bitter posteriorly. It moves food in ‘the buccal cavity for crushing under teeth, mixing with saliva and pushing the food during swallowing. Tongue cleans the teeth. It also aids in phonation (speech). It functions as a movable spoon during drinking.
      2. They are hard structures which are used for cutting, chewing and crushing the food (physical digestion). They are partially embedded in sockets of jaw bones (thecodont). Teeth are made of ivory like substance called dentine. The exposed parts of teeth or crowns are covered by a shining substance called enamel. Enamel is the hardest substance of the body.
      3. Salivary Glands. Three pairs of salivary glands (saliva secreting glands) open into buccal cavity. They are parotid (below ears), sub-maxillary (at the angles of lower jaw) and sublingual (below tongue). About 1-0-1-5 litres of near neutral saliva is poured into buccal cavity every day. Saliva consists of mucus, water, lysozyme and enzyme ptyalin.

      Question 40.
      Explain the process of breathing in man.
      Breathing or the process of taking in fresh air and releasing foul air can be easily observed because thorax shows alternate expansion and contraction. It is involuntary though it can be prevented for a brief period. Rate of breathing is controlled by respiratory centre of brain. Expansion of thorax causes fresh air to be drawn in. Contraction of thorax causes foul air to be expelled. Therefore, breathing consists of two steps, inspiration and expiration.

      1. Inspiration or Inhalation: It is bringing of fresh air into lungs for exchange of gases. During inhalation, thoracic cavity enlarges due to two types of inspiratory muscles, phrenic and external intercostals. Phrenic muscles straighten the diaphragm by moving its curved part downwards. It increases length of thorax. Contraction of external intercostal muscles pushes the rib cage in outward and upward direction. It increases girth of thorax. Being air tight, increase in size of thoracic cavity causes expansion of lungs. It decreases air pressure in the lungs. As a result outside air rushes into lungs through external nostrils, nasal cavities, internal nostrils, pharynx, larynx, trachea, bronchi, bronchioles to alveoli. While passing through respiratory tract, the incoming air is :
        1. Filtered by hair present in anterior part of nasal cavities.
        2. Cleansed of dust and microbes throughout respiratory tract by lysozyme, mucus and cilia.
        3. Air conditioned (bringing temperature of inhaled air to that of body) with the help of blood capillaries present below nasal epithelium.
        4. Moistened by water vapours from wet epithelium.

        Question 41.
        How do carbohydrates, proteins and fats get digested in human beings ?
        Carbohydrates: Glucose.
        Proteins: Amino acids.
        Fats: Fatty acids and glycerol.

        1. Carbohydrates: In mouth cavity (by saliva), duodenum (by pancreatic juice) and jejunum (by intestinal juice).
        2. Proteins: In stomach (by gastric juice), duodenum (by pancreatic juice) and jejunum (by intestinal juice).
        3. Fats: In duodenum and jejunum (by pancreatic juice aided by bile salts). Also in infants in stomach.

        Question 42.
        Explain the mechanism of photosynthesis.
        Mechanism of Photosynthesis:
        Photosynthesis is formation of organic food from carbon dioxide and water with the help of sunlight inside chlorophyll containing cells. Oxygen is produced as by-product.

        Oxygen comes from water. Hydrogen of water is used to reduce carbon dioxide to form carbohydrate.

        Actually, photosynthesis occurs in two steps, photochemical and biochemical.
        1. Photochemical Phase (Light or Hill Reaction): The reactions of this phase are driven by light energy. They are of two types— photolysis of water and formation of assimilatory power.
        (a) Photolysis of Water. Light energy splits up water into its components. Mn 2+ , CL and Ca 2+ are required for this.

        (b) Formation of Assimilatory Power: Light energy absorbed by chlorophyll molecules is used in synthesis of ATP and NADPH.
        Both ATP and NADPH2 together form assimilatory power.

        2. Biosynthetic Phase (Dark or Blackman’s Reaction). It is actually light independent reaction which can occur both in light as well as in dark. It requires the energy and reducing power contained in assimilatory power of light reaction. Common pathway of biosynthetic phase is Calvin cycle. Carbon dioxide combines with ribulose bisphosphate in the presence of enzyme ribulose biphosphate carboxylase or rubisco. It produces two molecules of phosphoglyceric acid (PGA).

        3. In the presence of ATP, phosphoglyceric acid is reduced by NADPH2 to form glyceraldehyde phosphate (GAP).

        4. A part of glyceraldehyde phosphate is changed into dihydroxyacetone phosphate. The two condense and form glucose. Ribulose biphosphate is regenerated to combine with carbon dioxide again. Glucose undergoes condensation to form reserve carbohydrate called starch.
        5. Other inorganic Raw Materials: Synthesis of carbohydrates during photosynthesis is a mechanism to form food materials for body building and releasing energy.

        Plants also require a number of other inorganic raw materials or minerals from soil for building other, e.g., nitrogen, phosphorus, iron, sulphur, magnesium, etc. Nitrogen and sulphur are required for building proteins. Phosphorus is required for synthesis of nucleotides. Minerals are absorbed in the form of ions, e.g., NO2 – and NH4 + for nitrogen. Some bacteria convert atmospheric nitrogen into compounds of nitrogen. Parts of them become available to plants.

        Question 43.
        Explain the three pathways of breakdown (respiration) in living organisms.
        (i) Aerobic Respiration:
        It is a multistep complete oxidative breakdown of respiratory substrate into carbon dioxide and water with the help of oxygen acting as a terminal oxidant. Aerobic respiration is the usual mode of respiration in all higher organisms and most of the lower organisms. The reason is that it yields maximum amount of energy. The energy is stored in some 38 molecules of ATP.

        Aerobic respiration occurs in two steps, glycolysis and Krebs cycle.

        Glycolysis: Glycolysis or EMP (Embden, Meyerhof and Parnas) pathway is the first step of respiration which is common to both aerobic and anaerobic modes of respiration. It occurs in cytoplasm. Respiratory substrate is double phosphorylated before it undergoes lysis to produce 3-carbon compound, glyceraldehyde phosphate. NADH2 and ATP are produced when glyceraldehyde is changed to pyruvate. The net reaction of glycolysis is :

        Krebs Cycle (Krebs, 1940): It is also known as citric acid cycle or tricarboxylic acid cycle (TCA cycle). Pyruvic acid or pyruvate passes into mitochondria. It undergoes oxidative decarboxylation to produce acetyl CoA, carbon dioxide and NADH2. Acetyl CoA enters Krebs cycle. Here two decarboxylations, four dehydrogenations and one phosphorylation or ATP synthesis occur.

        NADH2 and FADH2 liberate electrons and hydrogen ions. They are used in building up ATP molecules and activating oxygen molecules to combine with hydrogen for forming water. Synthesis of ATP from ADP and inorganic phosphate with the help of electron generated energy during oxidation of reduced coenzymes (NADH2, FADH2) is called oxidative phosphorylation. Water formed in respiration is called metabolic water. As oxygen is used at the end of Krebs cycle for combining with hydrogen, the process is called terminal oxidation.
        The overall equation of aerobic respiration using glucose as substrate is

        (ii) Anaerobic Respiration Producing Alcohol:
        It is a multistep breakdown of respiratory substrate in which atleast one end product is organic and which does not employ oxygen as an oxidant. Anaerobic respiration occurs in many lower organisms, e.g., certain bacteria, yeast. In human body it occurs regularly in red blood cells and during heavy exercise in muscles (striated muscles). Anaerobic respiration occurs entirely in the cytoplasm. It has two steps. The first step is glycolysis. Here, respiratory substrate glucose breaks down into two molecules each of pyruvate, ATP and NADH2. Pyruvate is converted into ethyl alcohol (C2H5OH) in Yeast and certain bacteria. It is changed to lactic acid (CH3CHOH.COOH) in muscle cells when oxygen utilisation is faster than its availability as during vigorous exercise. It creates an oxygen debt in the body. No such debt occurs in blood corpuscles.

        (iii) Anaerobic Respiration Producing Lactic Acid:
        Build up of lactic acid in muscles during prolonged activity causes fatigue and results in cramps.
        Fermentation (L. fermentum-froth). It is anaerobic breakdown of carbohydrates by microorganisms producing alcohol, organic acids and a variety of other products alongwith heat and waste gases. Fermentation is used in brewing industry (for producing wine, whisky, beer), baking industry (for making bread spongy), curd and yoghurt formation, synthesis of vinegar, citric acid, lactic acid, softening and aromatisation of Tobacco, Tea and other beverages, cleaning of hides and separating or retting of fibres (e.g., Jute, Hemp).

        Question 44.
        Describe the flow of blood through heart of human beings.
        It is passage of the same blood twice through the heart first on the right side, then on the left side in order to complete one cycle. Double circulation has two components, pulmonary circulation and systemic circulation.

        1. Pulmonary Circulation: It is movement of blood from heart to the lungs and back. Deoxygenated blood of the body enters the right auricle, passes into right ventricle which pumps it into pulmonary arch. With the help of two separate pulmonary arteries the blood passes into the lungs. Here, it is oxygenated. Oxygenated blood comes back to left auricle of heart through four pulmonary veins, two from each lung.
        2. Systemic Circulation: It is the circulation of blood between heart and different parts of the body except lungs. Oxygenated blood received by left auricle passes into left ventricle. The left ventricle pumps it into aorta for supply to different body parts including walls of the heart by means of arteries. Inside the organs the blood loses oxygen and nutrients. It picks up carbon dioxide and waste products. This deoxygenated blood is drained by veins and sent to the right auricle of heart.

        Question 45.
        Describe the process of urine formation in kidneys.
        Mechanism of Urine Formation:
        It has four components — glomerular filtration, selective reabsorption, tubular secretion and concentration.

        1. Glomerular Filtration: Blood flows in glomerulus under pressure due to narrowness of efferent arteriole. As a result it undergoes pressure filtration or ultrafiltration. All small volume solutes (e.g., urea, uric acid, amino acids, hormones, glucose, ions, vitamins) and water are filtered out and enter the Bowman’s capsule. The product is called nephric or glomerular filtrate. Its volume is 125 ml/min (180 litres/day).
        2. Reabsorption: Nephric filtrate is also called primary urine. It passes into proximal convoluted tubule. The peritubular capillaries around PCT reabsorb all the useful components of nephric filtrate, e.g, glucose, amino acids, vitamins C, calcium, potassium, sodium, chloride, bicarbonate and water (75%). Selective reabsorption also occurs in the region of distal convoluted tubule. The amount of water absorption depends upon amount of excess water present in the body and the amount of dissolved waste to be excreted.
        3. Tubular Secretion (Augmentation): It occurs mostly in the distal convoluted tubule which is also surrounded by peritubular capillaries. Smaller amount of tubular secretion also takes place in the area of proximal convoluted tubule. Tubular secretion is active secretion of waste products by the blood capillaries into the urinary tubule. It ensures removal of all the waste products from blood, viz.,’ urea, uric acid, creatinine. Extra salts, K + and H + are also secreted into urinary tubule to maintain a proper concentration and pH of the urine.
        4. Concentration of the Urine: 75% of water content of nephric filtrate is reabsorbed in the region of proximal convoluted tubule. Some 10% of water passes out of the filtrate through osmosis in the area of loop of Henle. It is because loops of Henle are immersed in hyper-osmotic interstitial fluid, Further concentration takes place in the area of collecting tubes in the presence of hormone called antidiuretic hormone (ADH) or vasopressin. The hormone is secreted only when concentrated urine is to be passed out. It is not secreted when a person drinks a lot of water. Absence of antidiuretic hormone produces a dilute urine. Hormone action, therefore, maintains osmotic concentration of body fluids. Deficiency of ADH causes excessive, repeated, dilute urination (diabetes insipidus).

        If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

        Types of Nutrition:

        1. Autotrophic Nutrition:

        i. Autotrophic nutrition is the mode of nutrition in which an organism prepares its own food.

        ii. Blue-green algae and Green plants follow the autotrophic mode of nutrition.

        2. Heterotrophic Nutrition:

        i. The mode of nutrition in which an organism takes food from another organism is called the Heterotrophic mode of nutrition.

        ii. Other than green plants and blue-green algae organisms show the heterotrophic mode of nutrition.

        iii. Heterotrophic nutrition can be further categorized into two types, viz. saprophytic nutrition and holozoic nutrition.

        3. Saprophytic Nutrition:

        i. In the saprophytic mode of nutrition the organism secretes the digestive juices on the food. The food is digested while it is still to be ingested.

        ii. The assimilated food is then consumed by the organism. All the decomposers follow saprophytic nutrition. Some insects like houseflies also follow this mode of nutrition.

        4. Holozoic Nutrition:

        i. In holozoic nutrition the digestion happens inside the body of the organism, i.e. after the food is ingested. Most of the animals follow this mode of nutrition.

        Different Types of Nutrition

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        Amphibian and Bird Respiratory Systems

        Birds and amphibians have different oxygen requirements than mammals, and as a result, different respiratory systems.

        Learning Objectives

        Differentiate among the types of breathing in amphibians and birds

        Key Takeaways

        Key Points

        • Amphibians utilize gills for breathing early in life, and develop primitive lungs in their adult life additionally, they are able to breathe through their skin.
        • Birds have evolved a directional respiratory system that allows them to obtain oxygen at high altitudes: air flows in one direction while blood flows in another, allowing efficient gas exchange.

        Key Terms

        Amphibian Respiration

        Amphibians have evolved multiple ways of breathing. Young amphibians, like tadpoles, use gills to breathe, and they do not leave the water. As the tadpole grows, the gills disappear and lungs grow (though some amphibians retain gills for life). These lungs are primitive and are not as evolved as mammalian lungs. Adult amphibians are lacking or have a reduced diaphragm, so breathing through the lungs is forced. The other means of breathing for amphibians is diffusion across the skin. To aid this diffusion, amphibian skin must remain moist. It has vascular tissues to make this gaseous exchange possible. This moist skin interface can be a detriment on land, but works well under water.

        Avian Respiration

        Birds are different from other vertebrates, with birds having relatively small lungs and nine air sacs that play an important role in respiration. The lungs of birds also do not have the capacity to inflate as birds lack a diaphragm and a pleural cavity. Gas exchange in birds occurs between air capillaries and blood capillaries, rather than in alveoli.

        Flight poses a unique challenge with respect to breathing. Flying consumes a great amount of energy therefore, birds require a lot of oxygen to aid their metabolic processes. Birds have evolved a respiratory system that supplies them with the oxygen needed to sustain flight. Similar to mammals, birds have lungs, which are organs specialized for gas exchange. Oxygenated air, taken in during inhalation, diffuses across the surface of the lungs into the bloodstream, and carbon dioxide diffuses from the blood into the lungs, and is then expelled during exhalation. The details of breathing between birds and mammals differ substantially.

        Bird Respiration: The process of inhalation and exhalation in birds. Three distinct sets of organs perform respiration — the anterior air sacs, the lungs, and the posterior air sacs.

        In addition to lungs, birds have air sacs inside their body. Air flows in one direction from the posterior air sacs to the lungs and out of the anterior air sacs. The flow of air is in the opposite direction from blood flow, and gas exchange takes place much more efficiently. This type of breathing enables birds to obtain the requisite oxygen, even at higher altitudes where the oxygen concentration is low. This directionality of airflow requires two cycles of air intake and exhalation to completely get the air out of the lungs.

        The Unicellular Tetrahymena as a Model Cellfor Receptor Research

        This chapter discusses the hormone reception of the tetrahymena. The tetrahymena, used as model cell in experiments, is a ciliated unicellular organism and as such a protozoan, the systematic position of which is very low in the phylogenetic order. As most ciliated unicellular organisms existing today are highly differentiated, they are considered primarily as independent organisms and only secondarily as single cells. As a unicellular organism, dependent greatly on its own resources for survival in a changing environment, the tetrahymena seems to be a suitable experimental model for the study of hormone receptors and their evolution. The superiority of the tetrahymena model to cells of higher organisms derives from the fact that it permits a comprehensive study of receptor formation and development from both the phylogenetic and the ontogenetic point of view—partly because the membrane of the tetrahymena is an intact structure with respect to hormonal influence and partly because, being a unicellular organism, its membrane is more dynamic than that of the cellular elements of organized tissues.


        iii) Taxon is defined as a taxonomic group or category such as phylum, order, family or genus that are used while classifying living organisms.

        1. What is meant by classification?
        • Classificationmeans identifying the similarities and dissimilarities between different kinds of organisms and placing the organisms with similar characteristics in one group and different organisms in different groups.
        1. Why do we classify organisms?
        • Classification makes the study of organisms much easier as there are millions of life forms and we cannot study them one by one. We can study the different classes or groups much easily after classifying them.
        1. Give three examples of range variations that you see in life forms around you.
        • Range of size: Microscopic bacteria of a few micrometre in size to blue whales and Redwood trees of California of approximate size of 30 metres and 100 metres respectively.

        (b) Range of lifespan: Pine trees living for thousands of years to insects like mosquitoes which die within a few days.

        (c) Range of colour: Life ranges from colourless worms to brightly coloured birds and flowers.

        1. What are the advantages in classifying organisms?
        • Organic evolution has been taking place for 3.5 billion years. It is impossible to study every living organism from an individual level. Therefore, classification is necessary to facilitate easy study of organisms.
        1. It makes the study of wide variety of organisms easy.
        2. It determines the method of organising the diversity of life on Earth.
        3. It helps to understand relationships and resemblances between various organisms
        4. It helps in understanding the evolution of organisms
        5. What is meant by characteristics?
        • Bycharacteristic, we mean a particular form or particular function that are used to classify the diverse group of organisms into groups. For example- The five fingers on each hand of human beings is a characteristic. Similarly, the ability of human beings to run unlike plants is also a characteristic.
        1. On what basis did Aristotle classify organisms? Was it a correct way of classification? Why?
        • Aristotle classified organisms according to whether they lived onland, in water or air and on physical difference. It was not a correct way of classification because animals which live in water differ in many different ways. Same is the case with those in air and on land. Habitat is the only point they share in common.
        1. What is the importance of putting organisms in groups?
        • With such a vast number of organisms – both living and extinct, it becomes impossible to study every one of them at individual level.
        1. ii) The task of studying the diversity of living organisms can be made easier and more effective if the various organisms are arranged in an orderly manner.

        iii) It is also useful because it allows us to identify similarities and differences among living things.

        1. What is the primary characteristic on which the first division of organisms is made?
        • The primary characteristic on which first division of organisms is based on whether the cells occur singly (unicellular) or they are grouped together and function as individual group (multicellular). Cell is considered to be the fundamental characteristic for classifying all living organisms.
        1. Which do you think is a more basic characteristic for classifying organisms?

        (i) The place where they live.

        (ii) The kind of cells they are made of why?

        Option (11).The kind of cells they are made up of is the more basic characteristic for classifying organisms. It is for the following reasons:

        (i) In every place, different types of organisms may live. They may not have similarities except for the common habitat.

        For example- An elephant and rabbit both live on land but they differ from each other in a number of ways. Moreover, further sub-classification is also not possible.

        (ii) Cells are the functional and structural unit of life. Primarily, we can differentiate an organism as unicellular or multicellular. Further sub-classification is also possible based on cell types, its complexity etc.

        1. What makes the basic distinction in the body design of organisms?
        • The type of cells whetherprokaryotic or eukaryotic is a characteristic that makes a basic distinction in the body design of organisms.
        1. Give three examples of characteristics used for hierarchical classification.
        • The three examples of characteristics used for hierarchical classification are

        (1) Prokaryotic or eukaryotic

        (2) Unicellular or multicellular

        (3) Mode of nutrition autotrophic or heterotrophic.

        1. On what basis are plants and animals put into different categories?
        • The basic design in plants and animals is different based on the need to make their own food (in plants) or acquire it (in animals).

        Plants are autotrophic means they can make their own food, whereas animals cannot.

        Locomotion is another characteristic which separates animal and plants in the classification.

        Their body designs are also different based on this characteristic.

        So, they are put into different categories.


        1. What is evolution?
        • Evolution is thegradual unfolding of organisms from the pre-existing ones through changes since the beginning of life.
        1. Which organisms are called primitive and how are they different from the so-called advanced organisms?
        • Groups of organisms which haveancient body designs that have not changed very much is called primitive or lower organisms. On the other hand, an organism acquired their particular body designs recently is called advanced or higher organisms.

        Primitive or lower organisms have simpler body design whereas advanced or higher organisms have comparatively more complex body design. Primitive organisms are considered at the first ladder on the evolutionary scale while the advanced organisms are considered at successive ladders on the evolutionary scale.

        1. What do we mean by biodiversity?
        • The vastvariety and differences that are found in the living organisms of different ecosystems whether terrestrial, aquatic or marine collectively known as biodiversity.
        1. Which region is known as the region of mega diversity?
        • The warm and humid tropical regions of the Earth, between thetropic of Cancer and the tropic of Capricorn, are rich in diversity of plant and animal life. This is called the region of mega diversity.
        1. Will advanced organisms be the same as complex organisms? Why? How can we say that the classification of life forms will be closely related to their evolution?
        • It is not always true that advanced organisms will have a complex body structure. But, there is a possibility that over the evolutionary time, the complexity in body design will increase. Therefore, at times, advanced organisms can be the same as complex organisms.

        (b) As the characteristics that have come into existence earlier are likely to be more basic than characteristics that have come into existent later.

        1. What are the five kingdoms that R. Whittaker proposed? Also define the term ‘species’
        • Whittaker categorized organisms in the following five kingdoms:

        Kingdom Monera, Kingdom Protista, Kingdom Fungi, Kingdom Plantae, kingdom Animalia.

        Species is a basic category of taxonomic classification, ranking below a genus or subgenus and having related organisms capable of interbreeding.

        1. Name the scientists who gave 2-kingdom and 5-kingdom classification respectively.
        • Two kingdom classification was given byCarolus Linnaeus

        Five kingdom classifications were given by Robert H. Whittaker


        1. What is the criterion for classification of organisms as belonging to kingdom Monera or Protista?
        • Kingdom Monera

        Organisms which are prokaryotes belong to the kingdom Monera. They are unicellularorganism which have no membrane bound nucleus and organelles.

        Kingdom Protista

        Organisms which are eukaryotes and unicellular belong to the kingdom Protista. They are organism with membrane bound definite nucleus and organelles.

        1. Name the levels of classification proposed by Linnaeus. What happens to the similarities among organisms as we go from top to bottom level?
        • Classification systems as proposed by Linnaeus use a hierarchical system in which organisms are placed into groups, at different levels, according to the features they share. These groups or levels are (from top to bottom)
        1. Kingdom
        2. Phylum
        3. Class
        4. Order
        5. Family
        6. Genus
        7. Species
        8. Name the scientist who described the idea of organic evolution and the book in which he explained it. Name the scientists who classified organisms into kingdoms.
        • Charles Darwinfirst described the idea of evolution in his book ‘The Origin of Species’.

        Ernst Haeckel, Robert Whittaker and Carl Woese is the scientists who classified organisms into kingdoms

        1. Define species
        • All organisms that are similar enough tobreed and perpetuate is called species.
        1. Explain the basis for grouping of organisms into five kingdoms:
        • The basis for grouping of organisms into five kingdoms is-

        (i) Nature of cells– either prokaryotic or Eukaryotic

        (ii) Number of cells– Unicellular and multicellular

        (iii) Presence or absence of cell wall

        (iv) Mode of nutrition

        1. Who proposed division of Monera kingdom ? State the groups proposed
        • Carl Woese.

        (i) Archaebacteria or Archaea

        (ii) Eubacteria or Bacteria.

        1. Which are the beings that constitute the kingdom Monera?
        • The kingdom Monera is the kingdom of the prokaryotes, composed of bacteria and archaebacteria.
        1. What are the important features of Kingdom Monera?
        • Kingdom Monera: It includes mainly bacteria, blue-green algae, or cyanobacteria

        Important features of Monera:

        – Absence of well-defined nuclear or membrane-bound organelles- prokaryotic organisms.

        – All of them are unicellular

        – Can be autotrophic (like Cyanobacteria) orheterotrophic (mostly parasitic or saprophytic)

        – Bacteria, blue-green algae and mycoplasma are the example organism belonging to the Monera kingdom.

        1. Why blue green algae are included under Monera and not under Plantae?
        • Nuclear material is not enclosed with nuclear membrane and cell organelles are also not enclosed with membrane.

        (ii) Do not show multicellular body design.

        1. What are the important features of Kingdom Protista?
        • Kingdom Protista: It Includes protozoans such as, Amoeba, Paramecium, diatoms etc

        Important features of protista:

        Unicellular, eukaryotic organism

        The cell has well defined nucleus with nuclear membrane and organelles.

        Cell wall may or may not be present.

        Can be autotrophic or heterotrophic

        Examples-Unicellular algae- Chlamydomonas, Euglena, Diatoms and Protozoans like Amoeba and Paramecium.

        1. Give one example of each Protesta having cilia and flagella.
        • Cilia – Paramecium.

        Flagella – Euglena.

        1. What are the important features of Kingdom Fungi?
        • Commonly known fungi are Yeast, mushroom, Penicillium, Aspergillus, etc.

        Important features of fungi:

        (i)Multicellular eukaryotic organisms

        Always heterotrophic (saprophytes) as they do not have chlorophyll and cannot prepare their own food by photosynthesis, live as saprophytes, parasites and symbiotic.

        (ii)Cell wall made of chitin, a complex nitrogen containing sugar that imparts toughness to cell wall.

        (iii)Mostly multicellular, only yeast is unicellular.

        (iv)Plant body contains thread-like hyphae (network is called mycelium).

        (v)Reproduction occurs by spore formation.

        Examples- Rhizopus, Aspergillius, Pencillium and Mushroom.

        1. What are saprophytes?
        • Saprophytes are organisms which usedecaying organic material as food. Eg., Rhizopus, yeast.
        1. Define moss.
        • Mosses are non-vascular plantsin the land plant division Bryophyta. Mosses reproduce using spores, not seeds and have no flowers. e.g., Funaria, Bryum, Sphagnum
        1. What is symbiotic? Give examples.
        • Symbiosis is a mode of heterotrophic nutrition. It is an interaction orinterrelationship between two organismsfor amutual benefitor dependence.

        Lichen is an example for symbiotic nutrition. It is an association between algae and fungi. Algae are autotrophic and can manufacture food for fungi while fungi provide shelter, water and minerals to algae.

        1. What are the important features of Kingdom Plantae?
        • Important features of Plantae:

        Multicellular eukaryotic organisms

        Most of the plants contain chlorophyll. Hence, they are autotrophic

        Cell wall made of cellulose is present

        1. What are the important features of Kingdom Animalia?
        • Important features of Animalia:

        Multicellular eukaryotic organisms

        Chloroplast is absent. Hence, they have heterotrophic mode of nutrition

        1. What is the difference between prokaryotic cell and Eukaryotic cell?
        • Eukaryotic cells containmembrane-bound organelles, such as the nucleus, while prokaryotic cells do not have membrane-bound organelles. The prokaryotes consists of bacteria and blue green algae and were first to rise in biological evolution

        The Eukaryotic cells are found in multicellular animals, plants and fungi. Eukaryotes have arisen probably a million year after prokaryotes and much larger and complex.

        1. State the major divisions in the Plantae:
        • Major division in Plantae are:-

        (i) Thalophyta.

        (ii) Bryophyte.

        (iii) Pteridophyta.

        (iv) Gymnosperms.

        (v) Angiosperms.

        1. State the criteria for deciding divisions in plants?
        • The criteria depends upon:-

        (i) Differentiation of plant body components.

        (ii) Presence of transport tissues (vascular tissues)

        (iii) Ability to produce seeds.

        (iv) Seedsareenclosed in fruits or naked.

        1. Describe the characteristic feature of thyllophytra with examples:
        • Thyllophyta includes mainly algae and these plants are predominantly aquatic.

        It includes Spirogyra, Ulothrix, Cladophora and Chara

        Plant body is thallus- not differentiated into true root, stem and leaves.

        May be unicellular or multicellular

        Cell wall is made of cellulose and reserve food material is starch.

        They have naked embryos called spores.

        1. What is a thallus?
        • Thallophyte has a simple plant body. The plantbody is not differentiated into root, stem and leaves and is called thallus.
        1. Why thallophytes are called non-embryonic plants?
        • Thyllophytes havesimple body (thallus) and their gametes are unicellular. After fertilisation, the zygote does not form an embryo. Therefore, these plants are called non-embryonic plants.
        1. Describe the characteristics feature of Bryophyta with examples:
        • Division Bryophyta are also called amphibians of plant kingdom:

        It includes mosses, Riccia, Marchantia

        Characteristic feature of Bryophyta:

        Vascular tissues namely xylem and phloem, or the conduction of water and other substances from one part of the plant body to another are absent.

        Body is differentiated into stem and leaf-like structures.

        Naked embryo called spores is present.

        1. Why bryophytes are called amphibians of the plant kingdom?
        • Bryophytes are also called amphibians of the plant kingdom because they canlive on soilbut needwater for sexual reproduction. They are usually found in damp, humid and shaded localities.
        1. Describe the characteristics feature of Pteridophyta with examples:
        • Division Pteridophyta: Includes ferns, Marsilea, Equisetum

        Characteristic feature of Pteridophyta

        Specialised vascular tissues for the conduction of water are present.

        Plant body is differentiated into true root, stem and leaves.

        Naked embryo called spores is present but seed formation is lacking

        1. What are the major divisions in the plantae? What is the basis for these divisions?
        • Major divisions of Kingdom plantae are-
        • Thallophyta
        • Bryophyta
        • Pteridophyta
        • Gymnosperms
        • Angiosperms
        • The division is based on the following features-

        (i)The first level of classification among plants depends on whether the plant body is well differentiated or not

        (ii)The next level of classification is based on whether the differentiated body has special vascular tissues (xylem and Phloem) for the transport of water and other substances.

        (iii)Further classification is based on the ability to bear seeds

        (iv)Further it is classified whether the seeds are naked or enclosed within the fruit.

        1. Name the two subkingdoms of plant kingdom.
        • Eichlerin 1883 suggested a system to classify the plant kingdom which is well accepted. He said that the plant kingdom is subdivided into two subkingdoms: Cryptogamae andPhanerogamae.
        1. What is the characteristic feature of cryptogamae? Name the 3 divisions included in it.
        • In Greek, crypto means concealed or hidden and ‘gamos’ means marriage.

        The cryptograms are flowerless and seedless plants. They are simple plants like algae, mosses and ferns which do not produce flowers, fruits and seeds. Since they do not have external flowers or seeds they are considered to have hidden reproductive organs. Theyreproduce through spores. The plant body in these organisms is undifferentiated, i.e, the stems, roots and leaves don’t show borders between them. Cryptograms are considered as lower plants.

        They are divided into bryophyta, thallophyta and pteridophyta.

        1. What are the characteristic features of sub kingdom phanerogamae?
        • This division is made up of plants thatbear flowers and seeds and make up the majority of the larger plants. The body is differentiated into true stem, leaves and roots. Propagation of the plant takes place with the help of seeds. Seeds are formed as a result of sexual reproduction. The male and female gametes (sex cells) fuse together inside the ovary (female part of the flower) and develop into the seed. In some plants seed is not produced inside an ovary.
        • Phanerogamae is made into two further divisions.

        (i)Gymnosperms (naked seeded plants)

        (ii)Angiosperms (Seed borne within a fruit)

        1. Describe the classifications of Phanerogams:
        • Phanerogams are divided into Gymnosperms and Angiosperms.

        (i)Gymnosperms: The term ‘Gymnosperms’ is made from two Greek words: gymno– means naked and sperma– means seed.

        Seeds are naked and reproductive organs are cones.

        They are non-flowering plants and are usually perennial, evergreen and woody. Example- Pinus, deodar, fir

        (ii)Angiosperms: The Word ‘Angiosperms’ is made from two Greek words: angio means covered and sperma– means Angiosperm have covered seeds(they are enclosed inside fruits)

        They are flowering plants and flowers are the reproductive organs.

        Example-Coconut, palm, mango

        1. How angiosperms are divided further?
        • Angiosperms are divided into 2 groups on the basis of the number of cotyledons present in the seed.

        (i)Monocotyledonous or monocots: These are the plants with seeds having a single cotyledon.E.g.Maize, wheat, rice etc

        (ii)Dicotyledonous or dicots: These are plants with seeds having two cotyledons. E.g., Pea, gram, bean etc

        1. Give uses of lichens.
        • (i)One of the most important uses of lichens is theirsensitivity to pollution.

        (ii) Lichens have been used for centuries to create natural dyes for fabrics.

        (iii) Many lichens contain acids and other essential oils that are useful in making perfumes and scents.

        1. iv) Some lichens are used inmedicines
        2. Ingestion of solid food occurs in which type of nutrition?
        • Ingestion of solid food occurs inholozoic type of nutrition.
        1. Name some edible fungi and their uses.
        • Edible fungi and their uses are as follows

        (i) Yeast has been used as leavening agent for the production of bread

        (ii) The first antibioticused in modern medicine, penicillin, was isolated form Penicillium

        (iii) Mushrooms have fleshy fruit body with certain aroma and flavors as well as good nutritional properties and are used mostly as food.

        (iv) Fungi such as the Chinese caterpillar fungus, which parasitize insects, can be extremely useful for controlling insect pests of crops

        1. Bacteria, fungi and plants all have the cell wall, but they are placed in the different groups or division. Why?
        • Bacteria, fungi and plants showed a characteristic difference in their walls composition –

        (i)In bacteria, the cell wall is made of peptidoglycans

        (ii)In fungi, the cell wall is made of chitin (the same substance that makes the exoskeleton of arthropods)

        (iii)In plants, the cell wall is made of cellulose too. Therefore, bacteria, fungi and plants are placed in the different groups or division.

        1. What is chemical characteristics of fungal cell wall?
        • In fungi, the cell wall is made ofchitin.
        1. Give one use of lichen.
        • Lichens are great indicators in telling us how polluted the air is, because lichens aresensitive to polluted airand are the first to disappear in that case.
        1. Classify the following seeds into dicot and monocot: Wheat, Maize, Bean, and Gram.
        • Dicot seeds – Bean, Gram.
        • Monocot seeds – Wheat, Maize
        1. While walking along roadside, Sunil asked his father, a biology teacher, whether some small, green, non-flowering, leafy and thalloid plants, having little differentiation of body and growing along pavement are of any use to us. Father answered that these plants are small but they play very important role in maintaining green cover on the land.

        (i) To which group these small thalloid, green, non-flowering plants belong?

        (ii) In what way bryophytes are useful to us?

        (iii)Which other groups of plants act as colonizers of barren rocks and make land suitable for growth of higher plants? Do these plants play some role in pollution monitoring?

        • (i)These small thalloid, green, non-flowering plants belong to the group calledbryophytes.

        (ii) Bryophytes are also used in horticulture as soil additives, ornamental material for cultivation, and for beautification of gardens.

        (iii) Mosses and Lichens act as colonizers of barren rocks and make land suitable for growth of higher plants. They are also good indicators of atmospheric quality.

        1. Why cotyledons are called seed leaves?
        • Cotyledons are actually part of the seed. They are thefirst part of the plant to emerge and they look like little green leaves (hence seed leaves). The cotyledons store food reserves for the growing seedlings. The plant relies on this stored food for early growth. The cotyledons can photosynthesise which supplies extra energy until the first true leaves emerge.
        1. Name the group of sessile animals that also have numerous pores all over the body?
        • Kingdom Porifera.
        1. What are the general characteristics found in all animals?
        • General characteristics found in all animals are-

        (i)All animals are multicellular, eukaryotic and heterotrophic

        (iii)Most of the animals have sense organs and nervous system

        (iv)Nutrition is generally ingestive

        (v)Reproduction is generally sexual.

        1. In how many phyla, the animal kingdom is divided into?
        • Kingdom Animalia is divided into nine phyla based on the extent and type of the body design differentiation found-

        Porifera (sponges)

        Coelentrata (jellyfish, corals etc)

        Platyhelminthes (flatworms)

        Nematoda (roundworms)

        Annelida (earthworms)

        Arthropoda (insects, spiders, crabs etc)

        Mollusca (snails, oysters etc)

        Echinodermata (starfishes, sea urchins etc)

        Chordata (animals with backbone)

        1. Why are air bladders present in fishes?
        • The air bladders help a fish to adjust its buoyancy in water. In other words it helps a fish float or sink no matter the size. Air bladder is also known as theswimbladder. The swim bladder allows the fish to move up and down through the water or remain motionless in one place.
        1. What are the characteristic features of Kingdom Porifera?
        • Porifera are pore-bearing animals called sponges.

        (i)Sponges are the simplest multicellular animals with cellular differention, lacking organization of tissues.

        (ii)They are mostly marine, fixed to the substratum and look like plants.

        (iii)The body has numerous pores on the surface, a cavity in the centre called spongocoel and a single large opening at the upper end called osculum.

        Circulating water canal system distributes food and oxygen to the entire cell

        (iv)The body is covered by a hard outside layer or skeleton.

        Reproduction occurs by regeneration, asexual and sexual methods.

        1. What are the characteristic features of Kingdom Coelenterate?
        • Coelenterates are aquatic mostly marine Hydra is found in fresh water.
        • They have tissue level of organisation.
        • Body is radically symmetrical
        • They have central cavity called coelenteron, which has one opening.
        • The body is made of two layers of cells: one makes up cells on the outside of the body, and the other makes the inner lining of the body.
        • Some of these species live in colonies (corals), while others have a solitary life–span (hydra).
        • Reproduction takes place by sexual and asexual methods.

        Hydra, jellyfish and sea anemones are common examples.

        1. Define radial symmetry?
        • Radial symmetry means that theleft and the right halves of the body have the samedesign.
        1. Name the following :

        (a) Free living Platyhelminthes

        (b) Scientific name of pork tape worm.

        1. Why are Protozoa regarded as early animals?
        • Protozoa are regarded as early or primitive animals because

        (i) They have a cellular grade of organization, e.g. Amoeba, paramecium.

        (ii) A single cell performs all functions therefore there is no division of labour.

        (iii) They are microscopic and exhibit a primitive mode of reproduction.

        1. What is the common name of annelids?
        • Segmented worms.
        1. Name the locomotory organs in insects.
        • Many adult insects use six legs for walking. ie. They havethree pairs of jointedlegs that allows for rapid walking while always having a stable stance (posture). They also have two pairs of wings that are mostly used for flying.
        1. What are the characteristic features of platyhelminthes?
        • The characteristic features of platyhelminthes-

        (i)The body is flat, leaf-like or tape-like, bilaterally symmetrical (left and right side of the body are similar)

        (ii)They are triploblastic with organ system of organisation

        (iii)Respiratory and circulatory systems are under developed

        (iv)Excretion occurs through flame cells

        (v)The nervous system is primitive but with a brain

        (vi)They are either free-living or parasitic. Some examples are free-living animals like planarians, or parasitic animals like liver flukes.

        1. Why are members of phylum Platyhelminthes called as flatworms?
        • Members of phylum Platyhelminthes are called flatworms because their bodies are flatteneddorso-ventrally, meaning from top to bottom. Therefore, these creatures have aleaf-like or ribbon-like They include Fasciola hepatica (liver fluke), Taeniasolium(tapeworm), Schistosoma (blood fluke), Planaria etc
        1. Define triploblastic animals?
        • Animals having a body made ofthree germ layers namely, ectoderm, mesoderm and endoderm. Platyhelminthes are the first triploblastic animals.
        1. What are the characteristic features of Nematoda?
        • Thephylum Aschelminthes is also known as Nematoda, and its members are nematodes. The members of this phylum are roundworms, and many are microscopic.

        The characteristic features of Nematode are-

        (i)The nematode body is also bilaterallysymmetrical and triploblastic.

        (iii)Organ grade body organisation is found

        (iv)They also have a digestive tract open at both the mouth and anus. This tract is suspended in a body cavity that is said to be false, so it is called a pseudocoel.

        (v)These are very familiar as parasitic worms causing diseases, such as the worms causing elephantiasis (filarialworms) or the worms in the intestines (roundworm or pinworms).

        1. What are the characteristic features of Annelida?
        • The characteristic features of Annelids are-
          • Annelids are segmented worms
          • They are triploblastic and bilaterally symmetrical
          • They have true body cavity (coelome).
          • This allows the true organs to be packaged in the body structure
          • Extensive organ differentiation is found
          • Digestive system is well developed
          • Respiration is through gills or skin
          • Circulatory system is usually closed.
          • These animals are found in a variety of habitats– fresh water, marine water as well as land. Earthworms and leeches are familiar examples
          1. Which are the morphological features that differentiate the beings of the phylum Annelida from nematodes and platyhelminthes?
          • Platyhelminthes are worms with flat bodies (flatworms), nematodes are worms with cylindrical but not segmented bodies (roundworms). Annelids are cylindrical worms with segmented bodies.
          1. DefineAschelminthes:
          • Aschelminthes is a phylum ofunsegmented, triploblastic, pseudocoelomate, cylindricalor thread-like worms having bilateral symmetry and body wall covered with cuticle and epidermis.
          1. Mention the characteristic features of Anthropoda?
          • The characteristic features of Anthropoda are-

          Anthropoda is the largest group of animals.

          These animals are triploblastic, bilaterally symmetrical and segmented.

          They have jointed legs (the word ‘arthropod’ means ‘jointed legs’).

          There is an open circulatory system, and so the blood does not flow in well-defined blood vessels.

          Coelomic cavity is blood-filled (haemocoel)

          Some familiar examples are prawns, butterflies, houseflies, spiders, scorpions and crabs

          1. Definehaemocoel:
          • When the coelomic cavity isfilled with blood, it is known as haemocoel.
          1. What is pseudocoelom?
          • The space betweenalimentary canal and body wall that lacks lining of mesodermal epithelium is known as pseudocoelom.
          1. Mention the characteristic features of Mollusca:
          • The characteristic features of Mollusca are-

          (i)They have soft body covered with a protective shell of calcium carbonate.

          (ii)There is bilateral symmetry.

          (iii)The coelomic cavity is reduced.

          (iv)There is little segmentation.

          (v)They have an open circulatory system and kidney-like organs for excretion.

          (vi)There is a foot that is used for moving around.

          Examples are snails and mussels

          1. Based of which character the phylum Echinodermata has been named?
          • In Greek, echinos means hedgehog, and derma means skin. Thus, these arespiny skinned Thus, the phylum Echinodermata has been named based on the presence of spiny skin.
          1. In which habitats do molluscs live? Name some examples of the phylum Mollusca?
          • Molluscs can be found in the sea, freshwater and in terrestrial environments. Snails, octopuses, squids and oysters are examples of molluscs.
          1. What is the morphological feature of molluscs after which the phylum is named?
          • The word “mollusc” means “soft thing”. Molluscs have soft bodies and this feature explains the name of the phylum.
          1. Which type of circulatory system do molluscs have? How can it be compared to the circulatory system of annelids?
          • With the exception of few, most of the molluscs have anopen circulatory system, i.e., the blood circulates within vessels, from the heart, but it also fills open cavities. In annelids, thecirculatory system is closed, i.e., the blood circulates only inside blood vessels.
          1. Mention the characteristic features of Echinodermata:
          • The characteristic features of Echinodermata-

          (i)In Greek, echinos means hedgehog, and derma means skin. Thus, these are spiny skinned organisms.

          (ii)These are exclusively free-living marine animals.

          (iii)They are triploblastic and have a coelomic cavity.

          (iv)They also have a peculiar water-driven tube system that they use for moving around.

          (v)They have hard calcium carbonate structures that they use as a skeleton.

          Examples are starfish and sea urchins.

          1. How can the endoskeleton of echinoderms be characterized in comparison to analogous structures present in vertebrates, arthropods and molluscs?
          • The echinoderm skeleton is internal, i.e., it is an endoskeleton. It is made of calcium carbonate (calcareous).
          • Vertebrates also have internal skeleton made of bones and cartilages.
          • Arthropods have an external carapace made of chitin, a chitinous exoskeleton.
          • Some molluscs present a calcareous shell that works as exoskeleton.
          1. What is osculum?
          • The body of sponge is porous and the pores are calledostia. Single large opening or pore is called osculum.
          1. Animals that belong to the phylum Coelenterata are diploblastic. What do we mean by diploblastic animals?
          • Diploblastic animal means animals havingbody made of two embryonic or germ layers of cells. Body walls of animals belonging to phylum coelenterata are made up of two germ layers, of which the outer layer is called ectoderm and inner is endoderm.
          1. Name two phyla which have open circulation:
          • Anthropoda, Mollusca and Echinodermata
          1. Which type of symmetry is present in-
          2. a) Starfish
          3. b) Earthworm
          • (a)Starfish- Radial symmetry

          (b) Earthworm- bilateral symmetry

          1. Mention the characteristic features of Protochordates
          • The characteristic features of Protochordates-

          (i)These animals are bilaterally symmetrical, triploblastic and have a coelom.

          Notochord is present in early stages of development, which may persist or disappear later.

          (ii)Protochordates are marine animals.

          Examples are Balanoglossus, Herdemania and Amphioxus

          1. What is a notochord? What does it do?
          • The notochord is along rod-like support structure (chord=string) that runs along the back of the animal separating the nervous tissue from the gut. It provides a place for muscles to attach for ease of movement.
          1. Mention the characteristic features of chordates:
          • All chordates possess the following features:

          (ii) All chordates have a dorsal nerve cord

          (iii) They are triploblastic

          (iv) They have paired gill pouches

          (v) Chordates are coelomate.

          1. What are the two mains divisions of the Phylum Chordate?
          • Chordates are divided intoprotochordates and vertebrates.
          1. How are animals belonging to protochordates different from animals belonging to vertebrates?
          • Animals that have notochord are categorized intochordata.
          • Some animals like Balanoglossus, Herdmania, Amphioxus etc. do not have a notochord, which is not present at all, stages in their lifecycle, nor does it run the entire length of an animal’s body. Therefore, these animals are kept in a separate sub-phylum named Protochordataunder phylum chordata.
          • In animals where the notochord is present throughout the life cycle and also has given rise to the vertebral column are calledvertebrates. The members of sub-phylum Vertebrata under Phylum Chordata are advanced chordates that include animals belonging to classes- Pisces,Amphibia, Reptilia, Aves and Mammalia..
          1. What are flame cells?
          • Flame cells areexcretory structures of Platyhelminthes. Besides excretion, they are also osmoregulatory in function.
          1. Why fungi are called saprophytes?
          • Fungi are known as saprophytes because they feed on dead and decaying organic matter.
          1. Name the locomotory organs of protozoans.
          • Locomotory organs of protozoans arecilia, flagella and
          1. Give one word for the following:
          2. The smallest unit of classification
          3. The largest unit of classification

          iii. A collection of related species

          1. Order
          2. What is meant by an incomplete digestive system?
          • Animals with an incomplete digestive system are those in which the digestive tube has onlyone opening (cnidarians, platyhelminthes).
          1. What are the characteristic features of vertebrates?
          • The members of the sub-phylum vertebrates are advanced chordates.
          • These animals have atrue vertebral column and internal skeleton, allowing a completely different distribution of muscle attachment points to be used for movement.
          • Vertebrates arebilaterally symmetrical,triploblastic, coelomic and segmented, with complex differentiation of body tissues and organs.
          • All chordates possess the following features:

          (ii) Have a dorsal nerve cord

          (iv) Have paired gill pouches

          1. What is the destination of the notochord in vertebrates and in protochordates?
          • In vertebrates, thenotochord disappears and gives birth to the spinal column (vertebral column). In protochordates, the notochord remains for the rest of the life.
          1. Explain how animals in vertebrata are classified into further subgroups:
          • Animals in vertebrata are classified into 5 classes namely
          1. What are the characteristic features of Pisces?
          • The characteristic features of Pisces are-
          • These are fish.
          • They are exclusively water-living animals.
          • Their skin is covered with scales/plate
          • They obtain oxygen dissolved in water by using gills.
          • The body is streamlined, and a muscular tail is used for movement.
          • They are cold-blooded and their hearts have only two chambers.
          • They lay eggs.
          • Some have skeletons made entirely of cartilage, such as sharks, and some with a skeleton made of both bone and cartilage, such as tuna or rohu
          1. What are the characteristic features of Amphibians?
          • The characteristic features of Amphibians are-

          (i)Amphibia are the first land vertebrates.

          (ii)They are adapted to live in water and on land.

          (iii)Skin is smooth without scales and has mucus glands in the skin to keep the skin moist.

          (iv)Respiration is through either gills or lungs.

          (v)They have a three-chambered heart and are cold-blooded animals.

          Frogs, toads and salamanders are some examples

          1. What are the differences between vertebrates and the other chordates?
          • Vertebrates are different because they have aspinal column (vertebral column). In these animals the notochord of the embryonic stage is substituted by the vertebral column in adults.
          1. How many carnivores belonging to cat family did you see in the zoo? What is given to them to eat?
          • Three (Lion, Tiger, Leopard) – Flesh of animals is offered to them for eating.
          1. Give scientific terms for the following:

          (a) True internal body cavity of animals.

          (b) A solid, unjointed rod present in chordates at some stage of life.

          (c) Creeping vertebrates.

          (d) Pore bearing animals.

          (b) Name the phyla in which animals have soft-bodies covered with a hard shell.

          (b) Phylum-Mollusca have animals that have soft bodies covered with a hard shell.

          1. Name two groups of warm blooded animals with four-chambered heart.
          • (i)Aves
          1. How is the skin of amphibians moist?
          • The skin of amphibians is moist because they are covered in a mucous coating.
          • Theysecrete mucusto help them keep their skin moist which aids in their ability to breathe through their skin. The mucous often contains other chemicals, like antibacterial or anti fungal to help protect the amphibian.
          1. How does amphibian overcome the unfavorable conditions?
          • Some amphibians become inactive when conditions are unfavorable for survival. This period of inactivity is calledaestivation when it occurs during hot, dry weather and hibernation when it occurs in response to cold temperatures. Activity resumes when favourable conditions return.
          1. Why do we keep both snake and turtle in the same class?
          • Both snake and turtle are kept in same class, because both

          (ii)Have thick tough skin with scales.

          (iv)Have three-chambered heart.

          1. What is a cold- blooded animal?
          • An animal whosebody temperature changes with the temperature of the environment is called cold- blooded animals. E.g., Frogs, snake, lizards etc.
          1. How is the skin of amphibians different from pisces and reptiles?
          • Skin is smoothwithout scales and hasmucus glands in the skin to keep the skin moist. Scales cover the skin of fishes to protect against water whereas reptiles skin has horny scales to protect against dry conditions.
          1. What are the five classes of vertebrates? To which of these do human beings belong?
          • The five classes of vertebrates are:fishes, amphibians, reptiles, birds and mammals. Humans classify as mammals.
          1. What is the group of the phylum Chordata that first colonized the terrestrial environment? From which habitat did they come?
          • Amphibians, partially aquatic partially terrestrial animals, were the first chordates that colonized the dry land. They came from the aquatic habitat and were originated from fishes. (Nevertheless the first completely terrestrial chordates were the reptiles).
          1. What are the characteristic features of Reptilia?
          • The characteristic features of Reptilia are
          • Reptilia are the first land vertebrates of the warmer regions.
          • Horny scales cover the horny skin.
          • These animals are cold-blooded
          • They breathe through lungs.
          • While most of them have a three-chambered heart, crocodiles have four heart chambers.
          • They lay eggs with tough coverings and do not need to lay their eggs in water, unlike amphibians.
          • Snakes, turtles, lizards and crocodiles fall in this category
          1. What are the characteristic features of Aves?
          • The characteristic features of Aves are-

          (i)These are warm-blooded animals and have a four-chambered heart.

          (iii)There is an outside covering of feathers, and two forelimbs are modified for flight.

          (iv)They breathe through lungs.

          (v)All birds fall in this category

          1. What are the characteristic features of Mammals?
          • The characteristic features of mammals are-
          • Mammals are warm-blooded animals with four-chambered hearts.
          • They have mammary glands for the production of milk to nourish their young.
          • Their skin has hairs as well as sweat and oil glands.
          • Most mammals familiar to us produce live young ones. However, a few of them, like the platypus and the echidna lay eggs, and some, like kangaroos give birth to very poorly develop young ones.
          1. What are the differences between animals belonging to the Aves group and those in the mammalian group?
          • In aves, body is covered with feathers while in mammals, body is covered with hairs. Mammary glands are absent in aves. Forelimbs of aves are modified into wings which is not the case in mammals. Aves are oviparous, while most of the mammals are viviparous.
          1. Mention the function and location of notochord.
          • Notochord is a supporting structure found in lower chordates and in embryos of all higher chordates. It functions as a major axial supporting structurejust as vertebral column does in our body and it runs along the back of the animal separating the nervous tissue from the gut.
          1. Rahul and his mother were walking in the garden. Rahul saw mushrooms growing on decaying leaves. He tried to uproot them. He was stopped by his mother.

          (i) Identify the kingdom to which the organism belongs to.

          (ii) Write the mode of nutrition exhibited by the mushrooms.

          (iii) Why did Rahul’s mother stop him?

          (iii) All mushrooms are not edible. Some mushrooms can sicken or kill you if eaten. That was the reason that Rahul’s mother stopped him.

          1. List a few flight adaptations in birds.
          • Flight adaptations of the birds are the following:
          • Their forelimbs have become modified into wings for flying.
          • Bird’s bones are hollow which makes birds’ bodies lightweight.
          • Birds have feathers that help them fly. The long flight feathers on the wings and tail help birds balance and steer.
          • The respiratory system of birds is also adapted to the demands of flight. Their bodies have air sacs helping them in double respiration
          • Keratin beak is much lighter than a bony jaw with teeth
          • Rapid, efficient digestion minimizes weight of digesting food.
          • Body is streamlined to reduce air resistance during its flight.
          • Ovaries and testes are reduced in size except in the breeding season.
          • Birds have short, light and compact body as compared to other animals.
          • Eyes are large, with wide field of view and binocular vision
          1. Why whales are not grouped in the fishes?
          • Originally, people thought that whales were very large fish because their bodies have a similar shape to that of fish. In 1778, Swedish biologist,Linnaeus, recognized that whales were not fish but mammals.

          They share some common characteristics of all mammals.

          1. They areendothermic: Their body-core temperature stays the same it does not change with the temperature of their environment.
          2. Theybreathe air with lungs.
          3. They givebirth to live young. Mothers (called cows) suckle their young (calves), on milk secreted by mammary glands.
          4. Theyhave hair. Although they are not covered in hair or fur like many mammals, whales have some bristles, usually on their heads.
          5. They havefour-chambered heart like mammals unlike fishes that have a two- chambered heart.
          1. Which group – Pisces or Amphibia is advanced? Give two reasons.
          • The group-Amphibia is advanced than Pisces because:

          (i) The amphibians have three-chambered heart whereas fishes have two-chambered heart

          (ii) Amphibians respire through gills or lungs while fishes have gills for respiration.

          (iii) Amphibians are adapted to live in both land and water whereas Pisces can live only in water.

          1. (i)Name an animal that gives birth to poorly developed young ones and nurtures them into full development after birth.

          (ii) Name two egg-laying mammals.

          (ii) Echidna, Platypus.

          (iii) Nomenclature

          1. What is meant by nomenclature?
          • Nomenclaturerefers to assigning a unique name to an organism. Two types of names have been given to organisms- Common name and scientific name.
          1. What is meant by scientific name?
          • A scientific name is the one given by biologists and represents a particular organism in every part of the world. Scientists ensure that a name being given by them has not been used earlier for any other organisms.
          1. What is meant by Binomial Nomenclature?
          • The system of scientific naming or nomenclature we use today was introduced byCarolus Linnaeus in the eighteenth century. The system developed by Linnaeus is known asBinomial Nomenclature.
          • Binomial Nomenclature is the system of assigning scientific names to plants and animals. It consists of two words, firstgeneric and second specific.
          1. What are the advantages of scientific name?
          • The names are universally accepted and understood.

          Every species has a specific name. No two species share a common specific name.

          The names indicate relationship of a species with others present in the same genus.

          (i) Amoeba Histolytica

          (ii) Atthalarosea (holly-hock)

          (iii) Brassica Comestris


          (ii) Alcearosea (common hollyhock)

          (iii) Brassica campestris

          (iv) Brassica oleracea (Cabbage)

          1. What is the scientific name of humans?
          • Homo sapiens.
          1. What conventions are followed while writing the scientific names?
          • Certain conventions are followed while writing the scientific names:
          1. The name of the genus begins with a capital letter. E.g., Panthera
          2. The name of the species begins with a small letter. E.g., tigris
          3. When printed, the scientific name is given in italics. E.g.,Pantheratigris
          4. When written by hand, the genus name and the species name have to be underlined separately
          1. Sheela shouted there is wall lizard in the room running on the wall. She started throwing shoes and other articles to hurt the lizard. Her mother came in the room and cools down the daughter and said it will not harm you. Do not hurt or kill it.

          Answer the following questions based on the above information:

          (a) Whether the wall lizard is poisonous?

          (b) What is its food and how can it run on the vertical wall?

          (c) Give one reason to justify that Sheela’s mother action is environment friendly.

          (b) It eats insects. Lizards have pads on their feet. These pads consist of wide plates or scales and are present below their fingers and toes. The outer layer of each plate or scale is composed of innumerable tiny hooks for-med by free, bent tips of cells. These minute hooks create the conditions like a suction pump and thus, enable lizards to run up on apparently smooth walls and even upside down on plaster ceilings.

          (c) Sheela’s mother avoided the killing of a living organism by clearing the myths that were believed by her daughter and maintain the food chain.

          1. During a field-trip some students visited an agricultural farm and saw a few birds eating earthworms. They enjoyed the scene and then they also started picking and killing the earthworms for pleasure. The farmer strongly objected and asked them to leave the field.

          Read the above passage and answer the following questions:

          (a) What could be the reason behind such behaviour of the farmer?

          (b) Which phylum do earthworm belong to?

          (c )Give any two identifying features of an earthworm

          (d) What values do you find missing in the student’s behaviour?

          • (a)The earthworm is considered to be the friend of a farmer since they further turn and loosen the soil .Like microbes, they also add humus to it by decomposing the dead plants and animals in the soil This was the reason on which farmer reacted.

          (b) Earthworm belongs to the phylum – Annelida.

          (c) Two identifying features of earthworm are

          (i) Segmented bodies are key identifying features of earthworms as well as important structural adaptations.

          (ii) Type and position of body bristles or satae.

          (d) Values which are missing in the student’s behaviour were destructive behaviour and sadistic behaviour of the kids

          How do Paramecia Move? (with pictures)

          Paramecia move with the assistance of small hairs called cilia that project from all sides of their bodies. The single-celled organisms use these hairs like oars, beating them against the water to move around in pursuit of food and to avoid predators. The movements are sometimes quite interesting to watch, as they are incredibly fast, considering their size. Almost any sample of still water will contain some paramecia. They are just visible with a magnifying glass, and sometimes with the naked eye, but can be seen in some detail with a microscope at around 100 X magnification.

          Paramecium Movement

          The way paramecia move is quite straightforward usually, they will travel in a straight line until they bump into something and navigate around it. They may, however, change course to reach food, and it is believed that the creatures may have chemical sensors to alert them to potential sources of nutrition. Watching one move around large obstacles can remind people of navigating into small parking spaces, as it moves forward, backs up, turn, moves forward, and so forth until it in the clear again.

          The cilia on a paramecium move in two directions. The creatures move forwards by beating their cilia at a backward angle, to thrust themselves through the water. To back up, they beat forwards. They also spin as they swim through the water, allowing them to collect food, which is pushed by the cilia into the mouth. A paramecium can look like a twirling top as it spirals through the water.

          How Cilia Work

          Many other single-celled organisms use cilia for propulsion, and some use a flagellum — a single, long, whip-like appendage. The two are quite similar in design, and operate in the same way. Although they appear to be just simple hairs, their structure is in fact quite complex.

          A cilium consists of a hollow, flexible cylinder, made from nine pairs of tiny tubes known as microtubules. Another pair of microtubules runs through the center, connected to the surface by spokes. Each pair of microtubules has two protein molecules, known as dynein arms, attached to it at intervals along its length. These act like tiny motors, using adenosine triphosphate (ATP) as a source of energy. To achieve movement, they push in unison against the neighboring microtubule pair, causing it to bend in the desired direction.

          This happens very quickly, and the combined action of these little motors causes the cilium as a whole to bend one way or the other, as required. Together, the coordinated action of many cilia can propel a paramecium at quite a speed, often making them difficult to observe clearly. The fine details of cilia cannot be seen with an ordinary microscope — their structure was revealed by examining cross sections using powerful electron microscopes. The study of cilia may help with the design of useful nanomachines.

          Observing Paramecia

          Paramecia can usually be obtained from pond or ditch water, especially near decaying vegetation such as dead leaves, which provide a rich food source in the form of bacteria and other microorganisms. A drop of this water placed on a microscope slide, with a cover slip on top, will usually reveal these little creatures. To see the cilia well, a magnification of perhaps 300-400 times is best, and it may be necessary to adjust the lighting to highlight these tiny, transparent structures.

          A common problem with observing paramecia, especially at higher magnifications, is that they simply move too fast for their detailed structure to be clearly seen. Scientists, therefore, sometimes resort to various methods of slowing them down. These include using viscous fluids, and providing food, such as yeast, which they will graze upon, reducing their movements.

          Interesting Paramecium Facts

          A paramecium is shaped roughly like a shoe or slipper, with a covering of cilia and a groove that acts as a mouth. The beating of the cilia, aside from providing propulsion, also creates currents in the water that drive food particles into the “mouth.” Despite being single celled, the organism is quite complex, with a nucleus containing genetic material, and easily identifiable organelles — miniature organs.

          Among these are one or more contractile vacuoles, which gather and expel excess water. Food particles, once “swallowed,” form food vacuoles: little “bags” that surround the food and through which nutrients are absorbed. By feeding paramecia yeast stained with a dye, the formation and progress of these vacuoles can be followed. Like most other single-celled organisms, paramecia usually reproduce by simply dividing in two — the nucleus splits first, duplicating the DNA. They are also capable of conjugation: a primitive form of sexual reproduction in which two organisms temporarily fuse together and exchange genetic material before dividing.

          Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

          Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

          How long can a unicellular organism live without nutrition? What happens after that? Does it depend on the domain? - Biology

          Anaerobic metabolic pathways allow unicellular organisms to tolerate or colonize anoxic environments. Over the past ten years, genome sequencing projects have brought a new light on the extent of anaerobic metabolism in eukaryotes. A surprising development has been that free-living unicellular algae capable of photoautotrophic lifestyle are, in terms of their enzymatic repertoire, among the best equipped eukaryotes known when it comes to anaerobic energy metabolism. Some of these algae are marine organisms, common in the oceans, others are more typically soil inhabitants. All these species are important from the ecological (O2/CO2 budget), biotechnological, and evolutionary perspectives. In the unicellular algae surveyed here, mixed-acid type fermentations are widespread while anaerobic respiration, which is more typical of eukaryotic heterotrophs, appears to be rare. The presence of a core anaerobic metabolism among the algae provides insights into its evolutionary origin, which traces to the eukaryote common ancestor. The predicted fermentative enzymes often exhibit an amino acid extension at the N-terminus, suggesting that these proteins might be compartmentalized in the cell, likely in the chloroplast or the mitochondrion. The green algae Chlamydomonas reinhardtii and Chlorella NC64 have the most extended set of fermentative enzymes reported so far. Among the eukaryotes with secondary plastids, the diatom Thalassiosira pseudonana has the most pronounced anaerobic capabilities as yet. From the standpoints of genomic, transcriptomic, and biochemical studies, anaerobic energy metabolism in C. reinhardtii remains the best characterized among photosynthetic protists. This article is part of a Special Issue entitled: The evolutionary aspects of bioenergetic systems.


          ► Many eukaryotic algae can generate ATP anaerobically via mixed acid fermentations. ► Algae use the same enzymes as heterotrophic eukaryotes for anaerobic energy metabolism. ► Enzymes of algal fermentations were present in the algal and eukaryote common ancestor. ► The H2-producing fermentations of Chlamydomonas are the best studied system to date. ► Anaerobic respirations in algae occur, for example nitrate, but have not been well-characterized.