Energy transfer between trophic levelsAQA A-Level Biology: Flashcards
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Question
State the equation for the net production of a consumer.
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- State the equation for the net production of a consumer.
- N = I − (F + R)
- What does I stand for in N = I − (F + R)?
- The chemical energy store in the ingested food.
- What does F stand for?
- Chemical energy lost to the environment in faeces and urine.
- What does R stand for?
- Energy lost in respiration.
- What is the net production of a consumer?
- The chemical energy stored in its new biomass, available for growth, reproduction and the next trophic level.
- How do you calculate the efficiency of energy transfer?
- Net production at the higher level ÷ net production at the lower level × 100.
- Give three reasons why energy transfer between trophic levels is not 100 % efficient.
- Not all is eaten; not all eaten is absorbed (faeces and urine); energy is lost in respiration as heat.
- Why is some food lost as F?
- Some of the food is not digested or absorbed, so its energy leaves the consumer in faeces.
- What happens to the energy in dead organisms and faeces?
- Bacteria and fungi feed on it, using some as respiratory substrates, so energy is lost as heat.
- Which organisms consume biological molecules made by photosynthesis?
- Animals, bacteria and fungi.
- Why do endotherms convert less of their intake to biomass than ectotherms?
- They use more energy in respiration to release heat and maintain a constant body temperature.
- A cow ingests 250 MJ, loses 90 MJ in F and 110 MJ in R. What is N?
- 250 − (90 + 110) = 50 MJ.
Exam questions on Energy transfer between trophic levels
- A dairy cow grazes on a pasture. During one day, the chemical energy store in the grass she ingests is 250 MJ. She loses 90 MJ in faeces and urine and releases 110 MJ in respiration.Calculate the net production of the cow in MJ per day and express it as a percentage of the energy she ingests.2 marks
- An ecologist studies a food chain in an estuary. The net primary production of the phytoplankton is 20 000 kJ m⁻² year⁻¹. The net production of the zooplankton that feed on them is 2 400 kJ m⁻² year⁻¹, and the net production of the small fish that feed on the zooplankton is 360 kJ m⁻² year⁻¹.Calculate the efficiency of energy transfer from the zooplankton to the small fish.2 marks
- In an oak woodland the net primary production of the trees is 14 000 kJ m⁻² year⁻¹. Herbivorous insects consume 1 400 kJ m⁻² year⁻¹ of this. Most of the rest falls to the ground as leaf litter and dead wood, and a small amount is stored as new wood in the living trees.Calculate the percentage of the trees' net primary production that is consumed by herbivorous insects, and suggest two reasons why most of the net primary production is not consumed by them.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).