The following sub-topics are covered in this section. 

(a) The organism in the environment 

(b) Feeding relationships 

(c) Cycles within ecosystems 

(d) Human influences on the environment

Students should: 

4.1 understand the terms population, community, habitat and ecosystem 

4.2 practical: investigate the population size of an organism in two different areas using quadrats 

4.3B understand the term biodiversity 

4.4B practical: investigate the distribution of organisms in their habitats and measure biodiversity using quadrats 

4.5 understand how abiotic and biotic factors affect the population size and distribution of organisms

Students should: 

4.6 understand the names given to different trophic levels, including producers, primary, secondary and tertiary consumers and decomposers 

4.7 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer 

4.8 understand the transfer of substances and energy along a food chain 

4.9 understand why only about 10% of energy is transferred from one trophic level to the next

Students should: 

4.10 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion 

4.11B describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria (specific names of bacteria are not required)

Students should:

4.12 understand the biological consequences of pollution of air by sulfur dioxide and carbon monoxide 

4.13 understand that water vapour, carbon dioxide, nitrous oxide, methane and CFCs are greenhouse gases 

4.14 understand how human activities contribute to greenhouse gases 

4.15 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its consequences 

4.16 understand the biological consequences of pollution of water by sewage 

4.17 understand the biological consequences of eutrophication caused by leached minerals from fertiliser 

4.18B understand the effects of deforestation, including leaching, soil erosion, disturbance of evapotranspiration and the carbon cycle, and the balance of atmospheric gases