5.1.1

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

1

Species: a group of organisms that can interbreed and produce fertile offspring.

Habitat: the environment in which a species normally lives or the location of a living organism.

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.

Ecosystem: a community and its abiotic environment.

Ecology: the study of relationships between living organisms and between organisms and their environment.

5.1.2

Distinguish between autotroph and heterotroph.

2

Autotroph: an organism that synthesizes its organic molecules from simple inorganic substances.

Heterotroph: an organism that obtains organic molecules from other organisms.

5.1.3

Distinguish between consumers, detritivores and saprotrophs.

2

Consumer: an organism that ingests other organic matter that is living or recently killed.

Detritivore: an organism that ingests non-living organic matter.

Saprotroph: an organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion.

5.1.4

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

2

Only real examples should be used from natural ecosystems. indicates that A is being “eaten” by B (that is, the arrow indicates the direction of energy flow). Each food chain should include a producer and consumers, but not decomposers. Named organisms at either species or genus level should be used. Common species names can be used instead of binomial names. General names such as “tree” or “fish” should not be used.

5.1.5

Describe what is meant by a food web.

2

5.1.6

Define trophic level.

1

5.1.7

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

3

Students should be able to place an organism at the level of producer, primary consumer, secondary consumer, and so on, as the terms herbivore and carnivore are not always applicable.

5.1.8

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

3

5.1.9

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

1

No reference to communities where food chains start with chemical energy is required.

5.1.10

Explain the energy flow in a food chain.

3

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

5.1.11

State that energy transformations are never 100% efficient.

1

Reference to the second law of thermodynamics is not expected.

5.1.12

Explain reasons for the shape of pyramids of energy.

3

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, for example, kJ m–2 yr–1.

5.1.13

Explain that energy enters and leaves ecosystems, but nutrients must be recycled.

3

5.1.14

State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.

1

5.2.1

Draw and label a diagram of the carbon cycle to show the processes involved.

1

The details of the carbon cycle should include the interaction of living organisms and the biosphere through the processes of photosynthesis, cell respiration, fossilization and combustion. Recall of specific quantitative data is not required.

TOK: What difference might it make to scientific work if nature were to be regarded as a machine, for example, as a clockwork mechanism, or as an organism, that is, the Gaia hypothesis? How useful are these metaphors?

5.2.2

Analyse the changes in concentration of atmospheric carbon dioxide using historical records.

3

Data from the Mauna Loa, Hawaii, or Cape Grim, Tasmania, monitoring stations may be used.

5.2.3

Explain the relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect.

3

Students should be aware that the greenhouse effect is a natural phenomenon. Reference should be made to transmission of incoming shorter-wave radiation and re-radiated longer-wave radiation. Knowledge that other gases, including methane and oxides of nitrogen, are greenhouse gases is expected.

5.2.4

Outline the precautionary principle.

2

The precautionary principle holds that, if the effects of a human-induced change would be very large, perhaps catastrophic, those responsible for the change must prove that it will not do harm before proceeding. This is the reverse of the normal situation, where those who are concerned about the change would have to prove that it will do harm in order to prevent such changes going ahead.

TOK: Parallels could be drawn here between success in deterring crime by increasing the severity of the punishment or by increasing the chance of detection. If the possible consequences of rapid global warming are devastating enough, preventive measures are justified even if it is far from certain that rapid global warming will result from current human activities.

5.2.5

Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect.

3

Aim 8: Consider whether the economic harm of measures taken now to limit global warming could be balanced against the potentially much greater harm for future generations of taking no action now. There are also ethical questions about whether the health and wealth of future human generations should be jeopardized, and whether it is right to knowingly damage the habitat of, and possibly drive to extinction, species other than humans.

The environmental angle here is that the issue of global warming is, by definition, a genuinely global one in terms of causes, consequences and remedies. Only through international cooperation will a solution be found. There is an inequality between those in the world who are contributing most to the problem and those who will be most harmed.

5.2.6

Outline the consequences of a global temperature rise on arctic ecosystems.

2

Effects include increased rates of decomposition of detritus previously trapped in permafrost, expansion of the range of habitats available to temperate species, loss of ice habitat, changes in distribution of prey species affecting higher trophic levels, and increased success of pest species, including pathogens.

5.3.1

Outline how population size is affected by natality, immigration, mortality and emigration.

2

Aim 7: Simulation exercises can be performed.

5.3.2

Draw and label a graph showing a sigmoid (S-shaped) population growth curve.

1

5.3.3

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

3

5.3.4

List three factors that set limits to population increase.

1

5.4.1

Define evolution.

1

Evolution is the cumulative change in the heritable characteristics of a population.

If we accept not only that species can evolve, but also that new species arise by evolution from pre-existing ones, then the whole of life can be seen as unified by its common origins.

Variation within our species is the result of different selection pressures operating in different parts of the world, yet this variation is not so vast to justify a construct such as race having a biological or scientific basis.

5.4.2

Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures.

2

5.4.3

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

1

5.4.4

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

3

5.4.5

State that the members of a species show variation.

1

5.4.6

Explain how sexual reproduction promotes variation in a species.

3

5.4.7

Explain how natural selection leads to evolution.

3

Greater survival and reproductive success of individuals with favourable heritable variations can lead to change in the characteristics of a population.

Aim 7: Computer simulations can be performed.

5.4.8

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

3

Other examples could include: the changes in size and shape of the beaks of Galapagos finches; pesticide resistance, industrial melanism or heavy-metal tolerance in plants.

5.5.1

Outline the binomial system of nomenclature.

2

TOK: The adoption of a system of binomial nomenclature is largely due to Swedish botanist and physician Carolus Linnaeus (1707–1778). Linnaeus also defined four groups of humans, and the divisions were based on both physical and social traits. By 21st-century standards, his descriptions can be regarded as racist. How does the social context of scientific work affect the methods and findings of research? Is it necessary to consider the social context when evaluating ethical aspects of knowledge claims?

5.5.2

List seven levels in the hierarchy of taxa—kingdom, phylum, class, order, family, genus and species—using an example from two different kingdoms for each level.

1

5.5.3

Distinguish between the following phyla of plants, using simple external recognition features: bryophyta, filicinophyta, coniferophyta and angiospermophyta.

2

5.5.4

Distinguish between the following phyla of animals, using simple external recognition features: porifera, cnidaria, platyhelminthes, annelida, mollusca and arthropoda.

2

5.5.5

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

3

A dichotomous key should be used.