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IB Biology Objectives
Topic 4: Ecology and Evolution


Topic 1: Cells
Topic 2: The Chemistry of Life
Topic 3: Genetics
Topic 4: Ecology and Evolution
Topic 5: Human Health and Physiology
Topic 7: Cell Respiration and Photosynthesis
Topic 8: Genetics
Topic 9: Human Reproduction
Topic 10: Defense Against Infectious Disease
Topic 11: Nerves, Muscles, and Movement
Topic 12: Excretion
Topic 13: Plant Science
Option E: Neurobiology and Behaviour
Option H: Further Human Physiology

4.1.1 Define ecology, ecosystem, population, community, species and habitat.

  • Ecology - the study of relationships between living organisms and between organisms and their environment.
  • Ecosystem - a community and its abiotic environment
  • Population - a group of organisms of the same species who live in the same area at the same time
  • Community - a group of populations living and interacting with each other in an area
  • Species - a group of organisms which can interbreed and produce fertile offspring
  • Habitat - the environment in which a a species normally lives or the location of a living organism

4.1.2 Explain how the biosphere consists of interdependent and interrelated ecosystems.

  • In an ecosystem, organisms feed off of each other. This relation or interaction of organisms can be in the form of a food chain or a food web. The food chain is a linear and simple feeding relation, where one organism has one type of food and is eaten by one type of organism. However, a food web is a more complex and it includes more variety of organisms, each of which can feed on a variety of other organisms and is fed upon by a variety of organisms. These are not the only interactions that compose the biosphere, however. A remarkable diversity of animal interactions, as well as the work of plants, bacteria, fungus, and protists combine to influence the biosphere. Also, organic cycles such as the water cycle, the recycling of the respiratory products of animals (carbon dioxide) in photosynthesis, and the transpiratory return of water to the atmosphere in plants all play major roles as well.

4.1.3 Define autotroph (producer), heterotroph (consumer), detritovore and saprotrophs (decomposer).

  • Autotrophs - also known as producers, they can make their own food - main producers are photosynthesizers, which utilize the sun's energy and convert it into chemical energy, which they use to build their bodies. Considered net producers of CO2.
  • Heterotroph - are consumers, they feed on ready made organic material, they cannot synthesize their own food, and they are considered net producers of CO2.
  • Detritovore - organisms that feed by ingesting dead organisms (for example - crabs, earthworms and vultures).
  • Saprotrophs or decomposers- organisms that feed on dead organisms and products of living organisms. They secrete enzymes on these materials that cause decomposition, and then they absorb the resulting simple compounds into their bodies. So they do not ingest whole food, but rather, they absorb decomposed and digested food. Examples are bacteria and fungi.

4.1.4 Describe what is meant by a food chain giving three examples, each with at least three linkages (four organisms).

  • A food chain is a linear and simple feeding relation, where one organism has one type of food and is eaten by one type of organism. For example:
    Mosquito larva --------->beetle ---------->mouse------------>snake Plankton---------------->krill----------------->mullet------------->shark Earwig----------------->lizard--------------->shrew------------->owl Clams------------->starfish------------>sea otters------------>orcas

4.1.5 Describe what is meant by a food web.

  • A food web is more complex than a food chain and it includes a larger variety of organisms. Each of which feed on a variety of other organisms and they are in turn fed on by more organisms. Therefore, if one species becomes extinct the ecosystem will still be able to exist. A drawing will be inserted at a later date of a food web.

4.1.6 Define trophic level.

  • Trophic level - the division of species in an ecosystem on the basis of their main nutritional source. The trophic level that ultimately supports all others consists of autotrophs, or primary producers.

4.1.7 Deduce the trophic level of organisms in a food chain and a food web.















4.1.8 Construct a food web containing up to 10 organisms, given appropriate information.

  • Do it yourself. You can check back though for a picture which will be inserted at a later date.

4.1.9 State that light is the initial energy source for almost all communities.

  • Light is the initial energy source for almost all communities.

4.1.10 Explain energy flow in a food chain.

  • Energy losses between trophic levels include material not consumed or material not assimilated and heat loss through cell respiration.

4.1.11 State that when energy transformations take place, including those in living organisms, the process is never 100% efficient, commonly between 10-20%.

  • When energy transformations take place, including those in living organisms, the process is never 100% efficient, commonly between 10-20%.

4.1.12 Explain what is meant by a pyramid of energy and the reasons for its shape.

  • A pyramid of energy shows the flow of energy from one trophic level to the next in a community. The units of pyramids of energy are therefore energy per unit area per unit time.

4.1.13 Explain that energy can enter and leave an ecosystem, but that nutrients must be recycled.

  • Energy can enter and leave an ecosystem but nutrients must be recycled. Sun light is the main source of energy on this planet. It is absorbed by photosynthesizing organisms, which convert light to chemical energy. Nutrients must be recycled by obtaining them from other organisms or products of organisms.

4.1.14 Draw the carbon cycle to show the processes involved.







4.1.15 Explain the role of saprotrophic bacteria and fungi (decomposers) in recycling nutrients.

  • These organisms feed on dead organisms and products of living organisms. They secrete enzymes on these materials that cause decomposition, and then they absorb decomposed and digested foods. Examples include many species of bacteria and fungi. These are essential organisms to an ecosystem, since they cause recycling of materials between biotic and abiotic parts of the ecosystem.

4.2.1 Outline how population size can be affected by natality, immigration, mortality and emigration

  • Population size can be affected by natality (birth) because as birth rate increases, the population increases. The increase in a population is exponential, as the population increases so does the birth rate. Immigration is the arrival to the population from another area. This adds to the numbers in the total population. Mortality is death, and the mortality rate, like the birth rate, increases as the population increases. This, along with emigration (migration of population to another area) can help to stabilize population growth. In order for a population to be stable in size, Natality + immigration = mortality + emigration.

4.2.2 Draw a graph showing the sigmoid (S-shaped) population growth curve.














4.2.3 Explain reasons for the exponential growth phase, the plateau phase, and the transitional phase between these two phases.

  • The exponential growth phase exists because that is when the population has already begun to grow, but not a lot yet, and it rises quickly because there are no limiting factors yet and the resources are in unlimited amounts. The plateau phase begins when the organism hits it's carrying compacity, which is the maximum number of organisms in a population that can be supported by the environment at a certain time, in a certain ecosystem. The transitional phase in between these two phases occurs because this is when the limiting factors in the environment start to limit the increase, slowing the population increase.

4.2.4 Define carrying capacity

  • Carrying capacity is the number of organisms in a population that can be supported by the environment at a certain time, in a certain ecosystem.

4.2.5 List three factors which set limits to population increase.

  • Three factors that set limits to population increase are the availability of nutrients, the number of predators, and the accumulation of waste materials.

4.2.6 Define random sample

  • A random sample is when every object (people or things) have an equal chance of being chosen every time something is chosen.

4.2.7 Describe one technique used to estimate the population size of an animal species based on a capture-mark-release-recapture method.

  • Various mark and recapture methods exist. Knowledge of the Lincoln index is what is required.
    population size = (n(1) + n(2))/n(3)
    n(1) = number of individuals initially caught, marked, and released.
    n(2) = total number of individuals caught in the second sample.
    n(3) = number of marked individuals in the second sample.
    Although some simulations can be carried out (eg. sampling beans in sawdust), it is much more valuable if this is accompanied by a real exercise on a population of animals. The limitations and difficulties of the method can be fully appreciated and some notion of the importance of sample size can be explained. Make sure you understand that there is a need for choosing an appropriate method for marking organisms.

4.2.8 Describe one method of random sampling used to compare the population numbers of two plant species, based on quadrat methods.







4.2.9 Calculate the mean of a set of values.

  • Set of values (2, 7, 3, 16, 11, 4, 14) 2+7+3+16+11+4+14 = 57 57/7=8.143

4.2.10 State that the term standard deviation is used to summarize the spread of values around the mean and that 68% of the values fall within + or - 1 standard devation of the mean.

  • Standard deviation is used to summarize the spread of values around the mean and 68% of the values fall within + or - 1 standard deviation of the mean. This rises to about 95% for +or - 2 standard deviations.

4.2.11 Explain how the standard deviation is useful for comparing the means and the spread of ecological data between two or more populations.

  • A small standard deviation indicates that the data is clustered closely around the mean value. Conversely a large standard deviation indicates a wider spread around the mean. Details of statistical tests to quantify variations between populations, such as standard error, or details about confidence limits are not required

4.3.1 Define evolution.

  • Evolution is the process of cumulative change in the heritable characteristics of a population, the descent of modern organisms from preexisting life forms.

4.3.2 State that populations tend to produce more offspring than the environment can support.

  • Populations tend to produce more offspring than the environment can support.

4.3.3 Explain that the consequence of the potential overproduction of offspring is the struggle for survival.

  • The world has limited resources. Organisms produce many more offspring than can live off of these limited resources. Therefore, there is a struggle to survive between offspring. This allows for natural selection, because those best suited for thier environment survive and pass on their better-suited genes.

4.3.4 State that the members of a species show variation.

  • The members of a species show variation.

4.3.5 Explain how sexual reproduction promotes variation in a species.

  • Sexually reproduction promote variations because, unlike the cloning that occurs in asexual reproduction ,every offspring in a genetic combination of his of her parents. This allows for infinite possibilities, as one can easily see by looking at the people around them. During meiosis, many different gametes are created because chromosomes are independently assorted during meiosis. Then, during fertilization, one of the many gametes from the mother joins with one of the many gametes from the father, creating a new and unique combination of genes.

4.3.6 Explain how natural selection leads to the increased reproduction of individuals with favorable heritable variations

  • Combining the ideas of the struggle to survive, and the great variation in organisms, we can see that a group of different organisms are all fighting to occupy a certain niche (a place in the ecosystem). If organism A is better suited for this environment than organism B, organism A will survive and reproduce more than organism B. It is very important to understand that longer life is not a "goal" of natural selection. An organism that is better suited to an environment will be able to reproduce and pass on thier superior genes. The ability of better sutied organisms to reproduce more than other organisms that are not as suited for thier environment allows for the better suited organisms to produce more organisms with those same genes. These organisms have inherited the superior genes, so the amount of organisms with superior genes has increased.

4.3.7 Discuss the theory that species evolve by natural selsction

  • In order to answer this question, the ideas aforementioned should be used.
  • If more organisms are produced that have "superior" genes, genes that make the organisms more suited for their environment, then they are able to produce more organisms with superior genes. This causes the population become more and more made of these superior organisms. When a population of a species changes as a result of natural selection, the species has evolved.

4.3.8 Explain two examples of evolution in response to environmental change; one must be multiple antibiotic resistance in bacteria

  • Example 1: Two varieties of the moth Biston betularia exist in the forms of different body color. One is black, the other is speckled. The black moth is easily seen by predators while the speckled one is camoulflaged. When on a tree covered in lichens, the peppered moth blends in very well. The number of speckled moths was greater than the number of black moths, because the speckled genes made the speckled moths more suitable for thier environment of lichenous trees. Because they were able to camouflage, they could evade predators more than black moths could, which allowed them to reproduce more moths with the genes for speckled color. Then, the trees began to get covered in suit due to the industrialization, and the black moth was able to be more camouflaged than the speckled moths. Because of this more black moths than speckled moths evaded predators, allowing them to produce more black moths. So the population of black moths then increased and the speckled moth population decreased.

    Example 2: Resistance to antibiotics in bacteria. If a culture of bacteria is sprayed with antibiotics, most of the bacteria is killed. A small number that naturally have genes resistant to antibiotics, will remain. It is important to note that these bacteria did not "learn" to resist antibiotics. These bacteria has mutated genes that somehow allowed them to resist antibiotics. These bacteria will reproduce and pass on thier resistant genes. Natural selection chose the antibiotic resistant ones, so those are the only ones to exist. This can become a problem when trying to kill a bacterial infection in a patient, because if the bacteria is resistant to the antibiotics given, then they can't be killed. Someone would have to come up with a new antibiotic that it is not resistant to, which can be difficult.

4.4.1 Define species.

  • Species - a particular kind of organisms; members possess similar anatomical characteristics and have the ability to interbreed and produce fertile offspring.

4.4.2 Describe the value of classifying organisms.

  • The number of species on this planet is huge and this requires a system of ordering and grouping that facilitate the process of studying and investigating the different aspects of these species. Similar species are grouped by their similar characteristics.

4.4.3 Outline the binomial system of nomenclature.

  • Organisms are given two names in this system (binomial). The first name indicates the genus and the second indicates the species. The genus is written in a capital letter and the species in small letters. Also the two names are usually printed or underlined. Naming organisms in this way facilitates the process of identification and helps in overcoming language barriers between scientists.

4.4.4 State that organisms are classified into the kingdoms Prokaryotae, Protoctista, Fungi, Plantae and Animalia.

  • Organisms are classified into the kingdoms Prokaryotae, Protoctista, Fungi, Plantae and Animalia.

4.4.5 List the seven levels in the hierarchy of taxa - kingdom, phylum, class, order, family, genus and species - using examples for each level.

  • Kingdom - Animalia
    Phylum- Chordata
    Class - Mammalia
    Order - Cetacea
    Family - Delphinidae
    Genus - Tursiops
    Species - truncatus
    -Bottlenose Dolphin-

4.4.6 Apply and/or design a key for a group of up to eight organisms.

  • Dichotomous key for: Blue whale, lobster, codfish, ant, monarch butterfly, honey bee, dove, and bat.

1. Is it aquatic (cannot survive on land)?

If yes, go to 2

If no, go to 4

2. Does it have gills?

If yes, go to 3

If no, it is a blue whale

3. Does it have legs?

If yes, it is a lobster

If no, it is a codfish

4. Does it have a body divided into 3 distinct parts: head, abdomen, and thorax?

If yes, go to 5

If no, go to 7

5.Does it have a stinging structure on its thorax?

If yes, it is a bee

If no, go to 6

6. Does it have wings with visible orange-and-black coloration?

If yes, it is a monarch butterfly

If no, go to 7

7. Does it have mandibles as its mouth parts?

If yes, it is an ant

If no, go to 8

8. Does it have feathers?

If yes, it is a dove

If no, it is a bat


4.5.1 Outline the two local or global examples of human impact causing damage to an ecosystem or the biosphere. One example must be the increased greenhouse effect.

  • The greenhouse effect is a naturally occuring phenomena in the ecosystem of the planet. It is simply the accumulation of carbon dioxide and other gases such as methane in the atmosphere, which traps heat from the sun's radiation and raises planetary temperatures. Recently, however, increased industry and burning of fossil fuels have caused the release of excessive amounts of carbon dioxide into the atmosphere. The planet is now enveloped by a layer of carbon dioxide far thicker than would be there naturally, which allows the sun radiation to enter our atmosphere, but prevents it from going out. This causes the trapping of heat into our atmosphere, and the consequent gradual increase in temperature around the world, hence global warming. This effect is called the greenhouse effect, since the layer of carbon dioxide around our planet has similar effects to the glass walls of a greenhouse in causing increased temperature inside.

    The ozone layer is present at about 20 Km above the surface of the earth. It absorbs ultra violet light that radiates from the sun, thus protecting us from the harmful effects of these radiations. Increased industry in the last 20 years or so, have caused the breaking of ozone molecules into oxygen, resulting in a hole in this protective layer. The chemicals responsible for this effect are a group of chlorofluoro carbons (CFCs) that are used in refrigeration, aerosol cans and other types of industry. These compounds are very light and they escape to the upper layers of the atmosphere, reaching the ozone layer and destroying it. A hole in the ozone layer is most prominent over the Antarctic.

4.5.2 Explain the causes and effects of the two examples in 4.5.1, supported by data.

  • The greehouse effect is largely a result of human industry and machinery, including automobiles and other vehicles that emit significant amounts of carbon dioxide from the burning of fossil fuels. Its effects have included an increase in global temperature by several degrees over the past decade, a melting of glacial deposits across the globe, and the recent thinning of Artic and Anartic pack ices; all of the effects reported as the much-publicized global warming. Many scientists predict more drastic changes in temperature and environment in the future if current warming patterns continue. Ozone depletion, as previously mentioned, is due to chemicals called CFCs being released into the atmosphere. CFCs, or chlorofluorocarbons, are a compound of chlorine, fluorine and carbon, as the name would suggest. They are found in refrigerants and a variety of aerosol containers. When these compounds are released into the atmosphere, by the action of spraying a can of hair spray, for example, they react with and break apart double-bonded oxygen molecules (ozone). One molecule of CFC can destroy thousands of ozone molecules; thus their large-scale release into the atmosphere during the 1980's and early 1990's was very damaging. The result was the opening of a large hole in the ozone layer (the atmospheric layer responsible for deflecting UV radiation from the sun harmful to most organisms) which was centered over Anartica. For several years the hole moved throughout the Southern Hemisphere, often exposing countries such as Austrailia to dangerously high amounts of UV radiation. Today the hole still exists, but since the banning of the production or use of CFCs it has shrunk considerably due to the repair of the ozone by natural causes.

4.5.3 Discuss measures which could be taken to contain or reduce the impact of the two examples, with reference to the functioning of the ecosystem.

  • The best method currently agreed upon to resolve the greenhouse effect issue is a twofold proposal. The first involves attempts to reduce the production of greenhouse gases by international treaties on the amount of gases emitted, such as the Kyoto Treaty, the use of alternative fuel and energy sources that emit little or no greenhouse gases, and improved filtering for industrial and automotive gases already produced. The second involves allowing the environment to stabilize this problem itself. This includes checking the destruction of forests and other photosynthetic environs and organisms, as these naturally regulate the amount of carbon dioxide in the atmosphere.