What this topic covers
Energy transfers in and between organisms (A-level only) has 4 subtopics:
- Photosynthesis (A-level only)
- Respiration (A-level only)
- Energy and ecosystems (A-level only)
- Nutrient cycles (A-level only)
← Back to topics
A Level AQA Biology · Topic 5 of 8
Energy transfers in and between organisms (A-level only) – A Level AQA Biology revision notes
Choose a subtopic. Energy transfers in and between organisms (A-level only) covers Photosynthesis (A-level only), Respiration (A-level only), Energy and ecosystems (A-level only), and Nutrient cycles (A-level only) in A Level AQA Biology. 12 lessons in 4 subtopics.
Revise Energy transfers in and between organisms (A-level only) for A Level AQA Biology, including Photosynthesis (A-level only).
12
Lessons
4
Subtopics
Energy transfers in and between organisms (A-level only) lessons by subtopic
12 lessons, grouped by subtopic.
Photosynthesis (A-level only)
- Photosynthesis: Light-Dependent Reactions: Explain how chlorophyll absorbs light and undergoes photoionisation, releasing high-energy electrons; Describe how ATP and reduced NADP are produced using energy from photoionised electrons; Explain the chemiosmotic theory of ATP synthesis, including the role of the electron transfer chain, proton gradients, and ATP synthase
- Photosynthesis: Light-Independent Reactions (Calvin Cycle): Describe the sequence of reactions in the Calvin cycle, naming the key molecules RuBP, GP, and triose phosphate; Explain how ATP and reduced NADP from the light-dependent reactions are used to drive the light-independent reactions; Analyse the fate of triose phosphate, distinguishing between regeneration of RuBP and synthesis of organic compounds
- Limiting Factors and Agricultural Practices: Identify the environmental factors that limit the rate of photosynthesis; Explain how each limiting factor affects the biochemical processes of photosynthesis; Evaluate data relating to agricultural practices used to overcome limiting factors
Respiration (A-level only)
- Glycolysis and the Link Reaction: Describe the stages of glycolysis, including phosphorylation of glucose, production of triose phosphate, and oxidation of triose phosphate to pyruvate; Explain how ATP and reduced NAD are produced during glycolysis; Describe the link reaction, including the oxidation of pyruvate to acetate and the formation of acetyl coenzyme A
- The Krebs Cycle and Oxidative Phosphorylation: Describe the reactions of the Krebs cycle, including the role of acetylcoenzyme A and the products generated per turn; Explain how oxidative phosphorylation uses the electron transfer chain and chemiosmosis to synthesise ATP via ATP synthase; Analyse the role of reduced coenzymes (NADH and FADH2) as links between the Krebs cycle and oxidative phosphorylation
- Anaerobic Respiration and Required Practical: Explain why pyruvate is converted to ethanol or lactate during anaerobic respiration, linking this to the regeneration of oxidised NAD; Compare the two pathways of anaerobic respiration in animals and yeast, including the products and enzymes involved; Describe how the regeneration of oxidised NAD allows glycolysis to continue under anaerobic conditions
Energy and ecosystems (A-level only)
- Energy Flow and Productivity in Ecosystems: Explain how plants synthesise organic compounds and how these form biomass; Define gross primary production (GPP) and net primary production (NPP) using correct AQA terminology; Calculate NPP using the equation NPP = GPP - R
- Calculating Net Production and Efficiency: Calculate net production of consumers using the equation N = I - (F + R); Explain what each variable in the net production equation represents in biological terms; Calculate the efficiency of energy transfer between trophic levels
- Improving Energy Transfer in Agriculture: Explain how simplifying food webs reduces energy losses to non-human food chains; Explain how reducing respiratory losses within a human food chain improves energy transfer efficiency; Calculate net productivity of producers or consumers from given data
Nutrient cycles (A-level only)
- Decomposition and the Nitrogen Cycle: Explain the role of saprobionts in decomposition, including the processes of extracellular digestion and absorption; Describe the stages of the nitrogen cycle: saprobiotic nutrition, ammonification, nitrification, nitrogen fixation, and denitrification; Explain how bacteria carry out nitrification and denitrification, and the conditions that favour each process
- Mycorrhizae, Phosphorus, and Recycling: Explain the role of mycorrhizae in facilitating the uptake of water and inorganic ions, including phosphorus, by plants; Describe how nutrients are recycled within natural ecosystems, using the phosphorus cycle as an exemplar; Explain the vital role of microorganisms in recycling chemical elements such as phosphorus and nitrogen
- Fertilisers and Eutrophication: Learn about the use of natural and artificial fertilisers, their impact on ecosystems, and the environmental issues arising from their use, including leaching and eutrophication.
Revise Right Mocks '26
AQA A-Level Biology mock draft, 26–31 Oct. Draft coverage: Biology 7402/1 · Paper 1. Reviewed for an original-practice sitting; check student availability before registering. Marking and results will follow later, after separate approval. Eligible new accounts receive a five-day Pro trial when signup email verification completes. Previous trials keep their original expiry. After expiry, new papers need Pro unless you have an explicitly confirmed free sitting offer for this event. That offer adds no Pro time or AI learning. Saved attempts and released results remain readable. No card or automatic charge.
More in this course
Go back to the full A Level AQA Biology topic list, or practise this topic with past-paper questions.
Frequently asked questions
What is Energy transfers in and between organisms (A-level only)?
Energy transfers in and between organisms (A-level only) covers Photosynthesis (A-level only), Respiration (A-level only), Energy and ecosystems (A-level only), and Nutrient cycles (A-level only) in A Level AQA Biology. 12 lessons in 4 subtopics.
What happens in the Krebs cycle?
In the Krebs cycle, in the mitochondrial matrix, acetyl-CoA delivers a two-carbon acetyl group that combines with four-carbon oxaloacetate to form six-carbon citrate. The The Krebs Cycle and Oxidative Phosphorylation notes cover this in full.
What happens in the Calvin cycle?
In the Calvin cycle, in the stroma, rubisco fixes carbon dioxide onto RuBP, forming an unstable six-carbon intermediate that splits into two molecules of GP. The Photosynthesis: Light-Independent Reactions (Calvin Cycle) notes cover this in full.
What is oxidative phosphorylation?
Oxidative phosphorylation is ATP synthesis using energy from electrons carried by NADH and FADH2. The The Krebs Cycle and Oxidative Phosphorylation notes cover this in full.
What are the limiting factors of photosynthesis?
The main limiting factors of photosynthesis are light intensity, carbon dioxide concentration and temperature, and water availability can also limit the rate. The Limiting Factors and Agricultural Practices notes cover this in full.
What happens in the link reaction?
In the link reaction, in the mitochondrial matrix, pyruvate is decarboxylated, losing carbon dioxide, and oxidised to acetate, with NAD being reduced. The Glycolysis and the Link Reaction notes cover this in full.
What happens in the light-dependent reaction?
In the light-dependent reaction, on the thylakoid membranes, light causes photoionisation of chlorophyll in PSII, and photolysis of water replaces the lost electrons. The Photosynthesis: Light-Dependent Reactions notes cover this in full.
What is eutrophication?
Eutrophication is the sequence of events when excess nitrates and phosphates enter water: algae multiply into an algal bloom that blocks light, submerged plants die, and aerobic bacteria decomposing the dead material use up dissolved oxygen. The Fertilisers and Eutrophication notes cover this in full.
What are the stages of the phosphorus cycle?
In the phosphorus cycle, weathering of phosphate-containing rock releases phosphate ions into the soil. The Mycorrhizae, Phosphorus, and Recycling notes cover this in full.