WJEC A-Level Geography 601-8455-3
Coastal Landscapes
Glaciated Landscapes
Tectonic Hazards
Changing Places
Water and Carbon Cycles
Global Migration
Global Governance of the Oceans
EcosystemsContemporary theme
Economic Growth and Challenge: IndiaContemporary theme
Economic Growth and Challenge: ChinaContemporary theme
Development in an African ContextContemporary theme
Energy Challenges and DilemmasContemporary theme
Weather and ClimateContemporary theme
Fieldwork and Geographical Skills
Ecosystems
Ecosystem structure, energy flow and productivity
- 3 things to know
- A2 Unit 4
Overview
Trophic level, pyramid of energy and gross primary productivity.
What you need to know
Answer each one before you reveal it.
Name the trophic levels of a simple food chain.
Roughly what proportion of energy is transferred between trophic levels?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Define a trophic level.
Model answer
A trophic level is a position in a food chain, defined by how many steps an organism is from the original source of energy.
- 2
Name the trophic levels of a simple food chain.
Model answer
Producers, primary consumers, secondary consumers and tertiary consumers, with decomposers acting on every level.
- 3
Roughly what proportion of energy is transferred between trophic levels?
Model answer
About 10%, the rest being lost as heat through respiration and in material that is not eaten or not digested.
- 4
Explain why food chains rarely have more than four or five levels.
Model answer
So little energy remains after successive transfers that a further level could not support a viable population.
- 5
What is a pyramid of energy?
Model answer
A pyramid of energy shows the amount of energy passing through each trophic level in a given time, and it always narrows upwards.
- 6
Define gross primary productivity.
Model answer
Gross primary productivity is the total rate at which producers convert light energy into chemical energy through photosynthesis.
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