1. Communities & Ecosystems Stephen Taylor
IB Diploma Biology
Stephen Taylor
Photo: Wasp in Java, by Stephen Taylor ©

2. Assessment Statements Obj.
5.1.1
Define species, habitat, population, community, ecosystem & ecology. 1
5.1.2
Distinguish between autotroph and heterotroph. 2
5.1.3
Distinguish between consumers, detritivores and saprotrophs.
5.1.4
Describe what is meant by a food chain, giving three examples, each with at least four linkages.
5.1.5
Describe what is meant by a food web.
5.1.6
Define trophic level.
5.1.7
Deduce the trophic level of an organism in a food chain & food web. 3
5.1.8
Construct a food web containing up to 10 organisms, using appropriate information.
5.1.9
State that sunlight is the initial energy source for almost all communities.
5.1.10
Explain the energy flow in a food chain.
5.1.11
State that energy transfers are never 100% efficient.
5.1.12
Explain reasons for the shape of a pyramid of energy.
5.1.13
Explain that energy enters and leaves ecosystems, but nutrients must be recycled.
5.1.14
State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.
Command terms:
Assessment statements from: Online IB Biology Subject Guide

8. Food webs show all of the feeding relationships within a habitat.
Read this research article and generate a food web.
The state of the oceans, part 2: Delving deeper into the sea's bounty. John Tibbetts
This is a good thing.

9. Food webs show all of the feeding relationships within a habitat.
Read this research article and generate a food web.
The state of the oceans, part 2: Delving deeper into the sea's bounty. John Tibbetts
This is a good thing.

10. Food webs show all of the feeding relationships within a habitat.

11. Food webs show all of the feeding relationships within a habitat.

17. Outline the roles of bacteria in the nitrogen cycle.
(Total 6 marks)

18. Rhizobium / nitrogen-fixing bacteria lives in root nodules / symbiotic relationship with legumes; fixes nitrogen into ammonia; using energy from ATP;
Azotobacter / nitrogen-fixing bacteria lives free in soil; fixes nitrogen into ammonia;
Nitrosomonas / nitrifying bacteria converts ammonia to nitrite;
Nitrobacter / nitrifying bacteria converts nitrite to nitrate; Nitrosomonas and Nitrobacter live in well aerated soil / require good supply of oxygen;
Pseudomonas denitrificans / denitrifying bacteria converts nitrate to nitrogen; nitrate is used as terminal electron acceptor instead of oxygen; carries this out in low oxygen / badly aerated soil; 6 max Responses must include at least three types of bacteria to achieve full marks. Award [0] for responses with just the name of bacterium.

19. Explain how energy and nutrients enter, move through, and exit a food chain in an ecosystem.
(Total 8 marks)

20. energy enters from (sun)light; chloroplasts / plants / producers / autotrophs capture (sun)light; energy flows through the trophic levels / stages in food chain; energy transfer is (approximately) 10% from one level to the next; heat energy is lost through (cell) respiration; energy loss due to material not consumed / assimilated / egested / excreted; labelled diagram of energy pyramid; energy passes to decomposers / detritivores / saprotrophs in dead organic matter;
nutrient cycles within ecosystem / nutrients are recycled; example of nutrient cycle with three or more links; nutrients absorbed by producers / plants / roots; nutrients move through (food chain) by digestion of other organisms; nutrients recycled from decomposition of dead organisms; nutrients from weathering of rocks enter ecosystem; nutrients lost by leaching / sedimentation (eg shells sinking to sea bed); 8 max
(Plus up to [2] for quality)

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