13: Module 11: Diversity of Life I - Biology

13: Module 11: Diversity of Life I

BLGY1124 The Diversity of Life

Living Planet provides students with an overview of the evolution and diversity of life, from bacteria to mammals. As well as an overview of the evolutionary processes that have generated the world’s biodiversity, students will also learn about the key features that define key groups and the role of those taxa in ecological processes.


The goal of the module is to introduce all School of Biology students to biological principles from whole organisms to planetary scales. Key features include:

  • (i) an introduction to evolution as the mechanism by which biodiversity is produced,
  • (ii) a broad overview of key taxa,
  • (iii) a summary of ecological principles from population to community to ecosystem to biosphere.


The module will run over 11 weeks, beginning with the origins of life, then moving through the evolution of key taxa, and finishing with a summary of ecological principles.

Learning Outcomes

By the end of the module, students will be able to

  • - Understand the principles of evolution by natural selection and how they have created global biodiversity
  • - Explain the defining traits of a range of biological taxa, and the mechanisms by which they evolved.

Skills Outcomes

  • - Understanding the origin and diversity of life and why it is studied.
  • - Developing analytical skills through online MCQs

Topic 3: Transport

The transport of water and sugars in plants is carried out by vascular bundles which are made up of two main tissue types: xylem and phloem. The xylem tissue is made up of dead cells (tracheids) that lie end to end to form hollow tubes. The cell wall of the xylem is reinforced with lignin to provide more rigidity and prevent its collapse as water moves upwards through it. Xylem transports water and mineral ions only in a unidirectional way (i.e. from roots to leaves only).

By Kelvinsong – Own work, CC BY-SA 3.0, [modified]

  • Transpiration: water evaporates out of the stomata in the leaf, more water moves in from the xylem to replace it.
  • Adhesion: the attractive forces between the water molecules and the xylem wall.
  • Cohesion: the attractive force in between the water molecules.
  • Tension: the pulling force created by surface tension occurring in air spaces inside the leaves’ as they lose water due through evaporation.

By FeltyRacketeer6 – Own work, CC BY-SA 4.0,

Sugars are distributed around the plant through phloem tissue in a bidirectional way. Phloem tissue is made up of living cells called sieve tubes. These cells have sieve plates to allow the flow of sugars throughout the phloem and companion cells that provide energy for the active transport of sugars in and out of the phloem.

By Kelvinsong – Own work, CC BY-SA 3.0, [modified]

The Pressure-Flow hypothosis

The Pressure-Flow hypothesis also known as source-to-sink theory explains how sugars move through the phloem tissue. The source is the site where sugars are made (i.e. leaves) and the sink is any part of the plant that require sugar for growth and other metabolic functions.

Sugar production through photosynthesis in plant leaves results in phloem loading due the high sugar concentration at the source. This causes water in the xylem to flow into the phloem by osmosis. The pressure of water movement from the source to the sink forces the sugars to move along with it. At the sink, sugar is unloaded to parts of plants that need it, causing water to move out of the phloem and into the xylem again by osmosis.

By CNX OpenStax –[email protected]:[email protected]/Introduction, CC BY 4.0,

Animal circulatory systems

The circulatory system in animals is a network system that aids in the transport of gases and nutrients to nourish the cells while removing metabolic wastes such as urea. There are two types of circulatory systems: open and closed circulatory systems.

In an open circulatory system, open ended vessels fill a cavity known as haemocoel with blood-like fluid called haemolymph that is pumped by a simple tube heart. Exchange of nutrients and wastes occurs when cells and tissues interact with this haemolymph. The open system is commonly seen in invertebrates such as insects as shown below. Haemolymph does NOT however transport gases since invertebrates have a separate system for gas exchange.

Organisms that are larger in size such as mammals rely on a closed circulatory system as it is more efficient in transporting materials. In a closed circulatory system, the heart pumps blood containing gases, nutrients and wastes around the body through closed vessels. These vessels include arteries, veins, and capillaries.

  • Arteries have thick, muscular wall and carry oxygenated blood away from the heart
  • Veins have internal valves and thin muscular wall and carry de-oxygenated blood from rest of the body back to the heart
  • Capillaries are microscopic vessels that connect arteries and veins together

By Kelvinsong – Own work, CC BY-SA 3.0,

Unlike invertebrates, the heart of vertebrates is more efficient as it contains chambers. In humans, there are four chambers that separate oxygenated blood from de-oxygenated blood. This means that one system flows from the heart to lungs and back (Pulmonary circulation) and the other system flows from the heart to the body and back (Systemic circulation). This is described as a double circulatory system.

By OpenStax College – Anatomy & Physiology, Connexions Web site., Jun 19, 2013., CC BY 3.0,

Changes in fluid composition during circulation

The composition of the blood changes as it moves around an organism to distribute nutrients, gases and wastes. In animals, as blood moves through the lungs, the concentration of oxygen increases while carbon dioxide decreases due to the gas exchange in the alveoli.

In plants, fluid composition in the xylem and phloem changes as it moves around the plant. This includes an increase in sugar concentration in leaves due to photosynthesis and a decrease in sugar concentration in any growing parts of the plants that uses sugar. You will cover more examples about changes in composition in further details in your class.

Structures in plants and animals can be visualised using different technologies such as the light microscope. In animals, the light microscope can produce micrographs to visualise blood components and cells. You will be required to draw scaled diagrams and perform calculations to estimate the size of the cells.

Microscopic structures in plants can be observed using a light microscope. An example of a transverse section of a root is shown below.

11.5 Common Misconceptions about Evolution

Although the theory of evolution initially generated some controversy, by 20 years after the publication of On the Origin of Species it was almost universally accepted by biologists, particularly younger biologists. Nevertheless, the theory of evolution is a difficult concept and misconceptions about how it works abound. In addition, there are those that reject it as an explanation for the diversity of life.

Concepts in Action

This website addresses some of the main misconceptions associated with the theory of evolution.

Evolution Is Just a Theory

Critics of the theory of evolution dismiss its importance by purposefully confounding the everyday usage of the word “theory” with the way scientists use the word. In science, a “theory” is understood to be a concept that has been extensively tested and supported over time. We have a theory of the atom, a theory of gravity, and the theory of relativity, each of which describes what scientists understand to be facts about the world. In the same way, the theory of evolution describes facts about the living world. As such, a theory in science has survived significant efforts to discredit it by scientists, who are naturally skeptical. While theories can sometimes be overturned or revised, this does not lessen their weight but simply reflects the constantly evolving state of scientific knowledge. In contrast, a “theory” in common vernacular means a guess or suggested explanation for something. This meaning is more akin to the concept of a “hypothesis” used by scientists, which is a tentative explanation for something that is proposed to either be supported or disproved. When critics of evolution say evolution is “just a theory,” they are implying that there is little evidence supporting it and that it is still in the process of being rigorously tested. This is a mischaracterization. If this were the case, geneticist Theodosius Dobzhansky would not have said that “nothing in biology makes sense, except in the light of evolution.” 6

Individuals Evolve

An individual is born with the genes it has—these do not change as the individual ages. Therefore, an individual cannot evolve or adapt through natural selection. Evolution is the change in genetic composition of a population over time, specifically over generations, resulting from differential reproduction of individuals with certain alleles. Individuals do change over their lifetime, but this is called development it involves changes programmed by the set of genes the individual acquired at birth in coordination with the individual’s environment. When thinking about the evolution of a characteristic, it is probably best to think about the change of the average value of the characteristic in the population over time. For example, when natural selection leads to bill-size change in medium ground finches in the Galápagos, this does not mean that individual bills on the finches are changing. If one measures the average bill size among all individuals in the population at one time, and then measures the average bill size in the population several years later after there has been a strong selective pressure, this average value may be different as a result of evolution. Although some individuals may survive from the first time to the second, those individuals will still have the same bill size. However, there may be enough new individuals with different bill sizes to change the average bill size.

Evolution Explains the Origin of Life

It is a common misunderstanding that evolution includes an explanation of life’s origins. Conversely, some of the theory’s critics complain that it cannot explain the origin of life. The theory does not try to explain the origin of life. The theory of evolution explains how populations change over time and how life diversifies—the origin of species. It does not shed light on the beginnings of life including the origins of the first cells, which is how life is defined. The mechanisms of the origin of life on Earth are a particularly difficult problem because it occurred a very long time ago, over a very long time, and presumably just occurred once. Importantly, biologists believe that the presence of life on Earth precludes the possibility that the events that led to life on Earth can be repeated because the intermediate stages would immediately become food for existing living things. The early stages of life included the formation of organic molecules such as carbohydrates, amino acids, or nucleotides. If these were formed from inorganic precursors today, they would simply be broken down by living things. The early stages of life also probably included more complex aggregations of molecules into enclosed structures with an internal environment, a boundary layer of some form, and the external environment. Such structures, if they were formed now, would be quickly consumed or broken down by living organisms.

However, once a mechanism of inheritance was in place in the form of a molecule like DNA or RNA, either within a cell or within a pre-cell, these entities would be subject to the principle of natural selection. More effective reproducers would increase in frequency at the expense of inefficient reproducers. So while evolution does not explain the origin of life, it may have something to say about some of the processes operating once pre-living entities acquired certain properties.

Organisms Evolve on Purpose

Statements such as “organisms evolve in response to a change in an environment,” are quite common. There are two easy misunderstandings possible with such a statement. First of all, the statement must not be understood to mean that individual organisms evolve, as was discussed above. The statement is shorthand for “a population evolves in response to a changing environment.” However, a second misunderstanding may arise by interpreting the statement to mean that the evolution is somehow intentional. A changed environment results in some individuals in the population, those with particular phenotypes, benefiting and, therefore, producing proportionately more offspring than other phenotypes. This results in change in the population if the characters are genetically determined.

It is also important to understand that the variation that natural selection works on is already in a population and does not arise in response to an environmental change. For example, applying antibiotics to a population of bacteria will, over time, select for a population of bacteria that are resistant to antibiotics. The resistance, which is caused by a gene, did not arise by mutation because of the application of the antibiotic. The gene for resistance was already present in the gene pool of the bacteria, likely at a low frequency. The antibiotic, which kills the bacterial cells without the resistance gene, strongly selects for individuals that are resistant, since these would be the only ones that survived and divided. Experiments have demonstrated that mutations for antibiotic resistance do not arise as a result of antibiotic application.

In a larger sense, evolution is also not goal directed. Species do not become “better” over time they simply track their changing environment with adaptations that maximize their reproduction in a particular environment at a particular time. Evolution has no goal of making faster, bigger, more complex, or even smarter species. This kind of language is common in popular literature. Certain organisms, ourselves included, are described as the “pinnacle” of evolution, or “perfected” by evolution. What characteristics evolve in a species are a function of the variation present and the environment, both of which are constantly changing in a non-directional way. What trait is fit in one environment at one time may well be fatal at some point in the future. This holds equally well for a species of insect as it does the human species.

Evolution Is Controversial among Scientists

The theory of evolution was controversial when it was first proposed in 1859, yet within 20 years virtually every working biologist had accepted evolution as the explanation for the diversity of life. The rate of acceptance was extraordinarily rapid, partly because Darwin had amassed an impressive body of evidence. The early controversies involved both scientific arguments against the theory and the arguments of religious leaders. It was the arguments of the biologists that were resolved after a short time, while the arguments of religious leaders have persisted to this day.

The theory of evolution replaced the predominant theory at the time that species had all been specially created within relatively recent history. Despite the prevalence of this theory, it was becoming increasingly clear to naturalists during the nineteenth century that it could no longer explain many observations of geology and the living world. The persuasiveness of the theory of evolution to these naturalists lay in its ability to explain these phenomena, and it continues to hold extraordinary explanatory power to this day. Its continued rejection by some religious leaders results from its replacement of special creation, a tenet of their religious belief. These leaders cannot accept the replacement of special creation by a mechanistic process that excludes the actions of a deity as an explanation for the diversity of life including the origins of the human species. It should be noted, however, that most of the major denominations in the United States have statements supporting the acceptance of evidence for evolution as compatible with their theologies.

The nature of the arguments against evolution by religious leaders has evolved over time. One current argument is that the theory is still controversial among biologists. This claim is simply not true. The number of working scientists who reject the theory of evolution, or question its validity and say so, is small. A Pew Research poll in 2009 found that 97 percent of the 2500 scientists polled believe species evolve. 7 The support for the theory is reflected in signed statements from many scientific societies such as the American Association for the Advancement of Science, which includes working scientists as members. Many of the scientists that reject or question the theory of evolution are non-biologists, such as engineers, physicians, and chemists. There are no experimental results or research programs that contradict the theory. There are no papers published in peer-reviewed scientific journals that appear to refute the theory. The latter observation might be considered a consequence of suppression of dissent, but it must be remembered that scientists are skeptics and that there is a long history of published reports that challenged scientific orthodoxy in unpopular ways. Examples include the endosymbiotic theory of eukaryotic origins, the theory of group selection, the microbial cause of stomach ulcers, the asteroid-impact theory of the Cretaceous extinction, and the theory of plate tectonics. Research with evidence and ideas with scientific merit are considered by the scientific community. Research that does not meet these standards is rejected.

NEET Biology Class 11 Biology Notes for NEET – Download PDF

NEET Biology is actually an important section because it is one of the most goal-oriented subjects when students plan their preparations wisely. During the test, questions from biology are so understandable that a well-prepared student will never feel dissatisfied with his or her preparations. NEET Biology plays an important role in determining student achievement in the NEET exam, however, this does not mean that students can focus on two other subjects. To hold a chair at a tertiary medical or dental college, students are advised to hone their skills in Biology. The level of biology difficulty has increased over the years. As a complete analysis of NEET 2021, it was assumed that the test went well in the difficulty meter where among all the other categories, Biology was considered the simplest, followed by Chemistry and then Physics which was the most difficult and challenging section that time.

Preparation notes of Biology is required for students to prepare for the National Eligibility cum Entrance Examination. A standardized test set is designed for students to be admitted to medical colleges. Students who have studied biology as a subject in science stream can apply for the exam and begin preparing for the exam. Students can view notes, syllabus, mock tests here and more details can visit the official site

NEET Chapter Wise Weightage for Biology

Biology is one of those sections that must not be taken lightly. Forming 50% of NEET question paper, Biology will help you get enough marks to qualify the examination.

Every chapter in this section is important, however, candidates need distribute their time effectively amongst various chapters. One can refer to the table below for the chapter-wise weightage of NEET Biology and plan their study accordingly.

NEET Chapter Wise Weightage 2021 for Biology:

Biology Chapters and topicsAverage no. of Questions from the chapterWeightage of the chapter and topic (In percentage)
Plant Diversity712%
Plant Anatomy24%
Plant Morphology47%
Cell Biology & Cell Division610%
Plant Physiology813%
Plant Reproduction59%
Genetics & Biotechnology1524%
Biology in Human Welfare12%
Total 100%
Animal Diversity310%
Animal Tissue13%
Structural Organization in animals12%
Human Physiology1345%
Human Reproduction & Reproductive Health518%
Origin & Evolution310%
Animal husbandry13%
Human Health & Diseases39%
Total 100%

By looking at the NEET Exam Pattern, students can prioritize topics according to their marking weightage and difficulty level. While many students feel that the division of Animal & Plant Kingdom is difficult, some students find it fun to read. So, here on this page, we have come up with a unique way to help you master the test. To help you deal with all the important details of NEET Biology, we have brought you the key points in the article below. If you go down to the NEET syllabus into simple topics, then you will get over 10,000 ideas. StudyRate is STUDY platform offers the best of NEET readings to build your knowledge with the help of notes and other resources made by academic experts. If you complete all these concepts correctly, then it will be easier to crack the NEET 2021 exam.
Please, have a look!

Have a Better Understanding of Botany & Zoology

Biology is a broad field to study. Before we take you to the study essentials, we would like you to go through the basic information about the two crucial parts of NEET Biology.

1. Zoology

Zoology or Animal Biology is a very interesting yet complex subject of the NEET Biology Syllabus. The branch responsible for the study of Animal Kingdom includes architecture, embryology, evolution, classification, practices, and the distribution of both animals – living and extinct. Through Zoology, you can learn about how animals interact with the natural system.

Zoology is also about animal interactions with the ecosystem. It is a very interesting stream of Biology and works on the study of the Animal Kingdom and its structures, evolution, embryos, practices, classification, and the distribution of living and extinct animals. Students are advised to focus on topics such as Reproduction and Psychology while preparing for the exam.

Zoology mainly contains 45 questions in the test and among those, most are easy and limited to try. Considering the level of difficulty of animal questions, experts say that in the entrance test, about 35% of the questions have a high level of difficulty and 15% of questions have a simple level. Zoology comprises the important topics like –

  • Animal Diversity
  • Human Physiology
  • Animal Tissue
  • Human Reproduction
  • Cockroach
  • Evolution
  • Animal Husbandry
  • Human Health & Disease
2. Botany

Botany or Plant Biology, also known as Plant Science or Phytology is the crucial part of NEET Biology & Science of Plant Life. A person specialized in the field of plant study is known as Botanist or Plant Scientist. Botany also includes the Study of Fungi & Algae.

Modern Botany deals with plant structure, growth, differentiation, reproduction, biochemistry & primary metabolism development, disease & plant taxonomy.

Botany mainly consists of 50% questions of average difficulty level 35% questions are mainly of high difficulty level and 15% questions are of an easy level. On the other hand, topics like Genetics & Biotechnology carry high weightage followed by Ecology in the exam.

Some of the important topics of Botany are given below –

  • Plant Anatomy
  • Plant Morphology
  • Cell Biology & Cell Division
  • Biomolecule
  • Plant Physiology
  • Plant Reproduction
  • Genetics & Biotechnology
  • Biology in Human Welfare
  • Ecology
  • Plant Diversity

The preparation for the biology subject is not sufficient to appear for the National Eligibility cum Entrance Examination, students must prepare the physics and chemistry subjects also. The process of preparation of notes, important formula and mock tests are provided in the links given below.

Download 11th and 12th grade Biology Notes in pdf form. It will be especially helpful during small gaps between tests that you appear for. You can easily make a quick overview of all the topics by using it. It contains all the important points, formulas, etc. which greatly help the review to be more effective. So download it and you should pass it on to the best level of preparation. It will also help in preparing for various competitive exams such as NEET, AIIMS etc.Download Typed Notes for biology class 11 and 12 by clicking on links given below.

The intended subject specific learning outcomes.
On successfully completing the module students will be able to have:

An appreciation of the diversity of microbial life (bacteria, fungi unicellular and simple multicellular eukaryotes).
An understanding of plant structural and reproductive diversity and the colonisation of the land by plants.
An understanding that animals are multicellular heterotrophic eukaryotes with tissues that develop from embryonic layers.
An understanding of basic concepts in ecology and the conservation of biodiversity.
The ability to safely handle and conduct experiments on a range of organisms under defined laboratory conditions.

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The last chapter of the class 11 biology syllabus consists of the enlisted topics:

  • Hormones and glands
  • Endocrine system of human
  • Hormone action mechanism
  • Role of hormones as regulators and messengers
  • Hypo and hyperactivity disorders

Thus, the biology syllabus for class 11 covers an array of topics that can be helpful when perusing higher education. Needless to say, with ample career opportunities in this field after class 12th, choosing the right university and course can be a daunting task. Take the assistance of the experts at Leverage Edu through a 30 minutes free career counselling session and get all your queries cleared!

Watch the video: Why is biodiversity so important? - Kim Preshoff (January 2022).