Topic 2: The Ecosystem
Topic 2.1 Structure
2.1.1 – Distinguish between biotic and abiotic components of the ecosystem.
1. Using figure 1, identify two abiotic factors to which mangrove trees are adapted. [1] (2011 N2 1a)
Figure 1
2. Distinguish between biotic and abiotic factors. [2] (2013 M2 4a)
2.1.2 – Identify the term trophic level
2.1.3 - Identify and explain trophic levels in food chains and food webs selected from the local environment.
3. For an ecosystem you have studied, draw a food chain of at least four named species. [3] (2011 M1 3b)
4. Explain the flow of energy in food webs. [5] (2011 N2 4b)
5. Using figure 2, construct a food chain with four trophic levels. [2] (2013 M1 4a)
Figure 2
6. Using figure 2, suggest why the population of snakes might increase if all the foxes were killed. [1]
2.1.4 - Explain the principles of pyramids of numbers, pyramids of biomass, and pyramids of productivity, and construct
such pyramids from given data.
7. Explain why the pyramid of numbers in figure 3a has fewer producers than consumers. [1] (2011 M1 3a)
Figure 3a
Figure 3b
8. State one other type of pyramid used to show trophic levels. [1] (2011 M1 3c)
9. Evaluate pyramids of numbers as a method of representing the biotic components of an ecosystem. [2] (2011 M1 3d)
10. Deduce, giving a reason, whether the figure below could represent the transfer of energy in a terrestrial ecosystem.
[1] (2012 M1 3a)
2.1.5 - Discuss how the pyramid structure affects the functioning of an ecosystem.
11. Describe two ways in which the pyramid structure of an ecosystem may be changed by a named human activity. [2]
(2011 M1 3e)
12. Rachel Carson’s book Silent Spring drew attention to the environmental impact of DDT on top carnivores. Explain
the vulnerability of top carnivores to non-biodegradable toxins, such as DDT, entering food chains. [2] (2011 N1 2c(iv))
13. Explain why organisms at the top of the food chain in the Great Pacific Garbage Patch are likely to accumulate high
concentrations of persistent organic pollutants. [2] (2013 M2 1b)
2.1.6 - Define the terms species, population, habitat, niche, community and ecosystem with reference to local examples.
14. Define the term species. [1] (2012 M1 3b)
2.1.7 - Describe and explain population interactions using examples of named species.
15. With reference to the Figure 4 only, describe an example of both mutualism and predation. [2] (2010 N2 1a(iii))
(2011 N1 2a)
Topic 2.2 Measuring abiotic components of the ecosystem
2.2.1 List the significant abiotic (physical) factors of an ecosystem.
16. Compare and contrast the abiotic factors found in the straight path of the river with the abiotic factors of the
meandering part of the river. [3] (2012 N2 1a)
2.2.2 Describe and evaluate methods for measuring at least three abiotic (physical) factors within an ecosystem.
17. Describe a method for measuring changes in abiotic components of a named ecosystem affected by human
activity. [5] (2010 M2 4a)
Topic 2.3 Measuring biotic components of the system
2.3.1 Construct simple keys and use published keys for the identification of organisms.
18. Using the key, identify prey species A to F from the lower jaw bones found in owl pellets, from an open European
woodland. [3] (2010 M1 2a)
19. Suggest two visible characteristics of the organisms below which could be used to construct an identification key.
[1] (2012 M1 3d)
20. Suggest one limitation of using a key to identify an organism. [1]
2.3.2 Describe and evaluate methods for estimating abundance of organisms.
21. To estimate the populations of small mammals in a woodland, ecologists set traps in the area before sunset and the
following morning marked all the captured animals before releasing them again. (2010 M1 2b)
a. State what information the ecologists must record before releasing the animals. [1]
b. A week later the traps are set again as before. State what data must be recorded when the traps are opened
and explain how these data may be used to estimate the small mammal population in the area. [2]
22. Suggest one method that could be used to estimate tiger population. [1] (2012 M1 1b, 1c)
23. Outline one difficulty that might be encountered while collecting this type of data. [1]
2.3.3 Describe and evaluate methods for estimating the biomass of trophic levels in a community.
2.3.4 Define the term diversity.
2.3.5 Apply Simpson’s diversity index and outline its significance.
24. Figure 3 below shows the species composition of two areas of forest. There are 100 trees in each area of forest.
The Simpson’s diversity index for Ecosystem A is 1.38. Calculate Simpson’s diversity index for Ecosystem B. [2] (2012
M1 3c)
Topic 2.4 Biomes
2.4.1 Define the term biome
25. With reference to figure 3, identify the type of biome found in Iraq. [1] (2012 M2 1a)
2.4.2 Explain the distribution, structure and relative productivity of tropical rainforests, deserts, tundra and any other
biome.
26. With reference to the resource booklet only, state two biomes which represent the plains bison’s natural habitat. [1]
(2010 N2 1a (i))
27. Describe the distribution, structure, and relative productivity of a named biome, and suggest how these may be
affected by global warming. [6] (2010 N2 3a)
Topic 2.5 Function
2.5.1 Explain the role of producers, consumers, and decomposers in the ecosystem.
2.5.2 Describe photosynthesis and respiration in terms of inputs, outputs and energy transformations.
28. State the two material inputs of photosynthesis. [1] (2013 M2 1d)
2.5.3 Describe and explain the transfer and transformation of energy as it flows through an ecosystem.
29a. List four possible reasons why not all sunlight emitted by the sun is used by plants for photosynthesis. [2] (2011
M1 4d 4e 4f)
b. Explain, giving two reasons, why the net productivity of secondary consumers is much smaller than that of primary
consumers. [2]
c. Compare the energy efficiency of terrestrial and aquatic food production systems. [2]
30. State two processes that reduce the amount of sunlight reaching the Earth’s surface as the light travels through the
atmosphere. [1] (2010 M1 4a 4b)
2.5.4 Describe and explain the transfer and transformation of materials as they cycle within an ecosystem.
31. Using figure 4, construct a quantitative model to show the storages and flows in forest carbon cycling. [3] (2010 M2
1b)
2.5.5 Define the terms gross productivity, net productivity, primary productivity and secondary productivity.
32a. Define the term net primary productivity (NPP). [1] (2011 M1 4a 4b)
b. Define the term gross primary productivity (GPP). [1]
2.5.6 Define the terms and calculate the values of both gross primary productivity (GPP) and net primary productivity
(NPP) from given data.
33. Using the picture below, calculate the efficiency of total insolation (sunlight) to NPP in Figure 5. [1] (2011 M1 4c)
34. Using the figure below, calculate, as a percentage range, the proportion of global NPP used for human food
consumption in one year. [2] (2010 M1 4b)
35. Define the terms gross primary productivity (GPP) and net primary productivity (NPP). Explain, with referenc to two
contrasting biomes, why one biome will be more productive than the other. [7] (2012 M2 5b)
36. Explain why net primary productivity (NPP) rates are higher in some parts of the planet than others. [2] (2012 N1
3b)
Topic 2.6 – Changes
2.6.1 Explain the concepts of limiting factors and carrying capacity in the context of population growth.
37. Define carrying capacity. [1] (2013 M1 3b(i))
2.6.2 Describe and explain S and J population curves.
2.6.3 Describe the role of density‑ dependent and density‑ independent factors, and internal and external factors, in the
regulation of populations.
38. For humans, malaria can be a density-dependent factor. Outline the concept of density-dependent factors. [2]
(2011 N1 2b)
(2013 M1 6b(i))
39. State a density-depnendent factor that might affect the size of a named animal population. [1] (2013 M1 6b(i))
2.6.4 Describe the principles associated with survivorship curves including, K‑ and r‑ strategists.
40. Draw and label a survivorship curve for both a named K-strategist and r-strategist. [4] (2010 N2 5a)
41. Explain how K-strategists and r-strategists are linked to succession. [6] (2010 N2 5b)
42. The figure below shows survivorship curves for two different species, A and B.
a. State the type of scale used on the vertical (y) axis. [1]
b. Identify two reasons why species A is probably a K-strategist but species B is more likely to be an r-strategist. [2]
(2013 M1 6a)
2.6.5 Describe the concept and processes of succession in a named habitat.
43. With reference to the resource booklet only, identify one natural factor and one human factor which interrupt the
process of succession. [2] (2010 N2 1a (ii))
44. With reference to examples, distinguish between the terms succession and zonation. [4] (2012 M2 2a)
45. Explain the relationship between succession and equilibrium. [6] (2011 N2 5b)
46. The figure below shows how vegetation changes with altitude in the Andean mountain chain in South America.
a. State the pattern of vegetation shown in the figure. [1] (2012 N1 1a)
b. Identify two limiting factors in the alpine meadows. [2]
c. Suggest one way the pattern of vegetation might change as a result of global warming. [1] (2012 N1 1a)
47. Japanese knotweed can be described as a pioneer species. Define the term pioneer species. [1] (2012 N1 2a)
2.6.6 Explain the changes in energy flow, gross and net productivity, diversity and mineral cycling in different stages of
succession.
2.6.7 Describe factors affecting the nature of climax communities.
48. With reference to a named example of an ecosystem, explain why the climax community is more diverse and
therefore more stable, than a community which has been interrupted by human activity. [6] (2012 M2 2b)