1
Triple only
[1 mark]A food chain is: grass → grasshopper → frog → snake. Nothing eats the snake. Which statement about the snake is correct?
- It is at trophic level 3 and is a secondary consumer
- It is at trophic level 4 and is a primary consumer
- It is at trophic level 4 and is an apex predator
- It is at trophic level 1 and is a producer
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Answer: C C (1)
2
Triple only
[2 marks]Explain how decomposers break down dead animals.
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- they secrete enzymes into the environment / onto the dead material (1)
- small soluble food molecules then diffuse into the microorganism (1)
- do not accept decomposers eat / ingest the dead animal
3
Triple only
[3 marks]The table shows the biomass at each trophic level in a food chain. (a) A student draws a pyramid of biomass using a scale of 1 mm = 20 g per m². Calculate the length of the bar for the caterpillars. (1) (b) Calculate the efficiency of biomass transfer from the caterpillars to the blue tits. Give your answer as a percentage. (2)
| Trophic level | Organism | Biomass in g per m² |
|---|---|---|
| 1 | Oak leaves | 2000 |
| 2 | Caterpillars | 240 |
| 3 | Blue tits | 18 |
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- (a) 240 ÷ 20 = 12 mm (1)
- (b) 18 ÷ 240 × 100 (1)
- = 7.5% (1) allow 7.5 with no working for 2 marks
4
Triple only
[3 marks]Only about 10% of the biomass at one trophic level is transferred to the next. Explain why.
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- not all the ingested material is absorbed, some is egested as faeces (1)
- large amounts of glucose are used in respiration, and lost as carbon dioxide and water (1)
- water and urea are lost in urine (1)
- ignore energy 'used up' unqualified