AQA GCSE Biology (8461), Higher tier · Ecology › Trophic levels in an ecosystem
Practise Transfer of biomass. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Animals also lose water and one other waste substance in urine. Name this waste substance.
Urea
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Only some of the biomass at one trophic level is transferred to the next trophic level.
(a) Approximately what percentage of the biomass at one trophic level is transferred to the level above? Tick (✓) one box.[1]
1%
10%
50%
90%
(b) Which two of the following are reasons why biomass is lost between trophic levels? Tick (✓) two boxes.[2]
Some ingested material is egested as faeces
Some material is lost as carbon dioxide and water in respiration
Organisms at higher trophic levels are larger
Producers absorb all the light that reaches them
(c) Animals also lose water and one other waste substance in urine. Name this waste substance.[1]
Show the answer and mark scheme
(a)Answer: 10%
(b)Answer: Some ingested material is egested as faeces; Some material is lost as carbon dioxide and water in respiration
(c)Answer: Urea
urea
Question 2Medium7 marks
Food chains rarely have more than four or five trophic levels.
(a) Explain why.[3]
(b) A lake contains 50 000 kg of algae (trophic level 1). Assume that 10% of the biomass is transferred between each trophic level. Calculate the biomass at trophic level 4.[2]
(c) Explain how the loss of biomass between trophic levels affects the number of organisms at each level.[2]
Show the answer and mark scheme
(a)
only about 10% of the biomass is transferred from one trophic level to the next
so the biomass decreases rapidly along the food chain
there is not enough biomass at the top to support another trophic level
(b)Answer: 50 kg
50 000 × 0.1 × 0.1 × 0.1
50 (kg)
(c)
there is less biomass at each higher trophic level
so fewer organisms can be supported at higher trophic levels (especially as they are often larger)
Question 3Hard7 marks
A young bull eats 8.0 kg of grass (dry mass) each day. Each day:
3.0 kg of dry mass is egested in its faeces
4.6 kg of the absorbed material is used in respiration or lost in urine
the rest is used for growth.
(a) Calculate the mass of new tissue made each day.[1]
(b) Calculate the percentage of the biomass eaten that becomes new tissue.[2]
(c) Explain why a large proportion of the grass eaten by the bull is egested.[2]
(d) Farmed fish turn a much higher percentage of their food into new tissue than cattle do. Suggest why.[2]
Show the answer and mark scheme
(a)Answer: 0.4 kg
8.0 − 3.0 − 4.6 = 0.4 (kg)
(b)Answer: 5%
0.4 ÷ 8.0 × 100
5 (%)
(c)
grass contains a lot of cellulose / fibre that is difficult to digest
so not all of the ingested material is absorbed
(d)
cattle keep their body temperature constant, so they use a lot of glucose in respiration to keep warm
fish body temperature changes with the water, so less respiration is needed
fish food (pellets) is high in protein and easier to digest than grass
fish are supported by water, so less energy is used for movement / supporting the body