Levels of Organisation
Recap Levels of Organisation for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Learn the order of ecological organisation: individual, population, community and then the whole ecosystem.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Living organisms are organised into levels within an ecosystem, and photosynthetic organisms are always the starting point.
Plants and algae are the producers of biomass for life on Earth, because they make glucose using light energy. Feeding relationships are shown in food chains, in which producers are eaten by primary consumers, which are eaten by secondary consumers, which are eaten by tertiary consumers.
Consumers that kill and eat other animals are predators, and those eaten are prey. In a stable community, predator and prey population sizes rise and fall in cycles: as prey numbers rise the predators have more food and increase, which then reduces the prey numbers again.
Revision notes
Producers and consumers
Photosynthetic organisms — plants and algae — are the producers of biomass.
Primary consumers eat producers. Secondary consumers eat primary consumers. Tertiary consumers eat secondary consumers. Each is a trophic level in the chain.
Predators and prey
Consumers that kill and eat other animals are predators; those eaten are prey.
In a stable community, the numbers of predators and prey rise and fall in cycles.
Predator-prey cycles
As prey numbers increase, there is more food for predators, so predator numbers increase.
More predators eat more prey, so prey numbers fall. With less food, predator numbers then fall too, allowing prey numbers to recover. The predator peak always lags behind the prey peak.
Key points
- Plants and algae are producers of biomass.
- Primary consumers eat producers.
- Secondary consumers eat primary consumers.
- Predators kill and eat other animals.
- Predator and prey numbers rise and fall in cycles.
- The predator peak lags behind the prey peak.
Worked examples
Example 1
Explain why plants are described as producers. [2 marks]
Model answer
Plants use light energy to make glucose by photosynthesis (1 mark), producing the biomass that all other organisms in the food chain ultimately depend on (1 mark).
Example 2
Explain why the peak in predator numbers comes after the peak in prey numbers. [3 marks]
Model answer
As prey numbers increase there is more food available for the predators (1 mark), so more predators survive and reproduce and their numbers rise (1 mark). This increase takes time, so the predator peak occurs after the prey peak (1 mark).
Example 3
Explain what happens to the prey population when predator numbers are high. [2 marks]
Model answer
More prey are eaten, so the prey population falls (1 mark). With less food available, the predator numbers then fall as well (1 mark).
Common mistakes
Saying predators and prey peak at the same time.
The predator peak lags behind, because the population takes time to grow.
Calling a plant a consumer.
Plants are producers because they make their own food.
Getting the trophic order wrong.
Producer, primary consumer, secondary consumer, tertiary consumer.
Saying the cycles are irregular.
In a stable community they follow a regular repeating pattern.
Exam tips
- Learn the trophic levels in order.
- Explain the lag when describing predator-prey cycles.
- Say producers make biomass using light energy.
- Describe the cycle as a repeating loop in both directions.
Key terms
- Producer
- An organism that makes its own food by photosynthesis.
- Primary consumer
- An animal that eats producers.
- Predator
- An animal that kills and eats other animals.
- Prey
- An animal that is eaten by a predator.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.