AQA A Level Biology (7402) · Paper 2 and Paper 3
AQA A Level Biology 3.5 Energy Transfers Exam Questions
Free AQA A Level Biology exam questions by topic for 3.5 Energy transfers in and between organisms, with a mark scheme for every pack. Covers photosynthesis, respiration, energy and ecosystems, and nutrient cycles.
3.5 Energy Transfers exam questions by subtopic
4 question packs covering every part of the specification, with thousands of real past exam questions between them. Do not stop after a few: answer as many as you can, without notes, and mark each one with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA A Level Biology topic 3.5
Topic 3.5 opens Paper 2. It follows energy from light captured in photosynthesis, through respiration, and on through food chains, then covers how nitrogen and phosphorus are recycled. The biochemistry is detailed, so learn the location and products of each stage.
What you need to know for 3.5 Energy Transfers
- 3.5.1 The light-dependent reaction in the thylakoid membranes (photoionisation of chlorophyll, photolysis of water, ATP made by chemiosmosis and reduced NADP) and the light-independent reaction in the stroma (rubisco combines carbon dioxide with RuBP, GP is reduced to triose phosphate, RuBP is regenerated). Limiting factors.
- 3.5.2 Glycolysis in the cytoplasm, anaerobic respiration producing lactate or ethanol, the link reaction and Krebs cycle in the matrix, and oxidative phosphorylation using the electron transfer chain and chemiosmosis.
- 3.5.3 Biomass, gross and net primary production (NPP = GPP - R), net production of consumers (N = I - (F + R)), efficiency of energy transfer, and how farming increases efficiency.
- 3.5.4 The nitrogen cycle (saprobionts, ammonification, nitrification, nitrogen fixation and denitrification), the phosphorus cycle, mycorrhizae, fertilisers, leaching and eutrophication.
Common mistakes in 3.5 Energy Transfers
- Saying the light-independent reaction happens in the dark. It happens in the light too; it just does not use light directly.
- Forgetting that ATP and reduced NADP from the light-dependent reaction are used to reduce GP to triose phosphate.
- Missing the point of anaerobic respiration: it oxidises reduced NAD, regenerating NAD so glycolysis can continue to make ATP.
- Subtracting the wrong values in production calculations. NPP is GPP minus respiratory losses.
- Putting the steps of the nitrogen cycle in the wrong order. Nitrification is ammonium to nitrite to nitrate, by nitrifying bacteria in aerobic conditions.
Try three 3.5 Energy Transfers exam-style questions
1. Explain why producing lactate allows a muscle cell to keep making ATP during anaerobic respiration. (2 marks)
Show the mark scheme answer
Pyruvate is reduced to lactate, which oxidises reduced NAD; this regenerates NAD so glycolysis can continue.
2. The gross primary production of a field is 20 000 kJ m-2 year-1 and respiratory losses are 15 000 kJ m-2 year-1. Calculate the net primary production. (1 mark)
Show the mark scheme answer
20 000 - 15 000 = 5000 kJ m-2 year-1.
3. Describe what happens to carbon dioxide in the light-independent reaction. (3 marks)
Show the mark scheme answer
Carbon dioxide combines with RuBP, catalysed by rubisco; this produces two molecules of GP; GP is reduced to triose phosphate using ATP and reduced NADP.
Want more? Every pack above has many more past exam questions on energy transfers.
3.5 Energy Transfers FAQs
What does AQA A Level Biology topic 3.5 cover?
Topic 3.5, Energy transfers in and between organisms, covers photosynthesis, respiration, energy and ecosystems, and nutrient cycles.
Which AQA A Level Biology paper is topic 3.5 on?
Topic 3.5 is examined in Paper 2, which covers topics 3.5 to 3.8. Paper 3 can also include questions on any topic, so it is worth revising for that paper too.
Are these AQA A Level Biology 3.5 exam questions free?
Yes. Every question pack and mark scheme on this page is a free PDF download, with no sign-up needed.
