7.4 Food chains and predator-prey cycles
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In the food chain grass → rabbit → fox, name the producer and the secondary consumer.
Mark scheme
- producer: grass (1)
- secondary consumer: fox (1)
Model answer
The producer is the grass and the secondary consumer is the fox.
What do the arrows in a food chain represent?
Mark scheme
transfer of biomass / energy / "is eaten by"
Model answer
The direction in which biomass and energy are transferred, from the organism eaten to the one that eats it.
Explain why every food chain starts with a producer.
Mark scheme
- producers make glucose / biomass by photosynthesis (1)
- they are the source of all biomass / energy in the community (1)
Model answer
Producers make their own food by photosynthesis, so they are the source of all the biomass that is passed along the chain.
Explain why the numbers of foxes and rabbits rise and fall in cycles.
Mark scheme
- more rabbits means more food for foxes (1)
- so fox numbers rise (1)
- more foxes eat more rabbits so rabbit numbers fall (1)
- less food so fox numbers fall, then rabbits increase again (1)
Model answer
When there are many rabbits, foxes have plenty of food, so more foxes survive and breed. More foxes eat more rabbits, so rabbit numbers fall. Then foxes have less food and their numbers fall, so more rabbits survive and the cycle starts again.
On a predator-prey graph, the peak in predator numbers comes after the peak in prey numbers. Explain why.
Mark scheme
it takes time for predators to breed / reproduce in response to more food
Model answer
It takes time for the predators to breed and their numbers to increase after the food supply rises.
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