Edexcel A Level Biology B
Edexcel A Level Biology B Topic 5: Energy for Biological Processes Exam Questions
Free Edexcel A Level Biology B exam questions for Topic 5: Energy for Biological Processes, with a mark scheme for every pack. Covers ATP, glycolysis, link reaction, Krebs cycle, oxidative phosphorylation, anaerobic respiration, photosynthesis and photosynthetic pigments.
Topic 5: Energy for Biological Processes exam questions
8 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer 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 Edexcel A Level Biology B Topic 5: Energy for Biological Processes
Topic 5 of Edexcel A Level Biology B covers how organisms release and capture energy. You study aerobic respiration in detail, from glycolysis in the cytoplasm through the link reaction and Krebs cycle in the mitochondrial matrix to oxidative phosphorylation and chemiosmosis on the inner mitochondrial membrane. Anaerobic respiration in animals and yeast explains how NAD is regenerated when oxygen is limited. Photosynthesis is studied through the light-dependent reactions on the thylakoids and the light-independent reactions in the stroma, together with the photosynthetic pigments and how they are separated by chromatography. Questions often involve respirometer data and interpreting the effect of inhibitors on these pathways.
What you need to know
- Aerobic respiration overview Respiration releases energy from glucose to make ATP. The stages are glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation.
- Glycolysis Glucose is phosphorylated, split into two triose phosphates and oxidised to two pyruvate, with a net yield of two ATP and two reduced NAD.
- Link reaction and Krebs cycle Pyruvate is decarboxylated and oxidised to acetyl coenzyme A. In the Krebs cycle, acetyl CoA joins a four-carbon compound; decarboxylation and dehydrogenation produce CO2, reduced NAD, reduced FAD and ATP.
- Oxidative phosphorylation Electrons pass along the electron transport chain; protons are pumped into the intermembrane space and diffuse back through ATP synthase. Oxygen is the final electron acceptor.
- Anaerobic respiration In mammals pyruvate is reduced to lactate; in yeast it forms ethanol and CO2. Both regenerate NAD so glycolysis can continue.
- Photosynthesis and pigments Light-dependent reactions produce ATP, reduced NADP and oxygen. The Calvin cycle fixes CO2 with RuBP using RuBisCO to form GP, which is reduced to GALP. Pigments are separated by chromatography and identified by Rf values.
Common mistakes in Topic 5: Energy for Biological Processes
- Saying ATP stores large amounts of energy; it releases small, usable amounts when hydrolysed.
- Stating that anaerobic respiration produces no ATP; glycolysis still produces a net two ATP.
- Confusing NAD with NADP; NAD is used in respiration, NADP in photosynthesis.
- Placing the Calvin cycle on the thylakoids; it takes place in the stroma.
- Forgetting that oxygen from photosynthesis comes from the photolysis of water.
Try three Topic 5: Energy for Biological Processes exam-style questions
1. A pigment travelled 2.4 cm and the solvent front travelled 6.0 cm. Calculate the Rf value. (2 marks)
Show the mark scheme answer
2.4 / 6.0; = 0.40.
2. Explain why a respiratory inhibitor that blocks the electron transport chain stops the Krebs cycle. (3 marks)
Show the mark scheme answer
Reduced NAD and FAD cannot be oxidised; no NAD or FAD is regenerated; Krebs cycle dehydrogenation reactions cannot continue without them.
3. Describe what happens to pyruvate in the link reaction. (3 marks)
Show the mark scheme answer
Pyruvate enters the mitochondrial matrix; it is decarboxylated, releasing CO2; it is oxidised, producing reduced NAD; combines with coenzyme A to form acetyl CoA.
Topic 5: Energy for Biological Processes FAQs
What does Edexcel A Level Biology B Topic 5: Energy for Biological Processes cover?
It covers ATP, the stages of aerobic respiration, anaerobic respiration, the light-dependent and light-independent reactions of photosynthesis and photosynthetic pigments.
Which paper is Topic 5 examined in?
At A Level, this topic is assessed in Paper 1 and can also appear in Paper 3, which covers general and practical principles from all topics.
How do I learn respiration without getting lost in detail?
Draw each stage on one page showing its location, inputs, outputs and the number of ATP, reduced NAD and reduced FAD made, then practise linking the stages together.
