Respiration
Glycolysis, link reaction, Krebs cycle, oxidative phosphorylation, respiratory substrates, anaerobic pathways and respirometry.
How to study A-level Biology
Move between scales deliberately: identify the biological process, trace matter or information, use quantitative evidence, then evaluate the method and conclusion.
Core concepts
Concept 1
Respiration transfers energy from substrates through phosphorylation and redox reactions to ATP.
Exam cue: Track carbon atoms, reduced coenzymes and ATP rather than memorising isolated stage names.
Concept 2
Glycolysis occurs in the cytoplasm; later aerobic stages in mitochondria generate reduced coenzymes and an electrochemical gradient.
Exam cue: Explain oxygen as the final electron acceptor in oxidative phosphorylation.
Concept 3
Anaerobic pathways regenerate oxidised coenzyme but yield less ATP than complete aerobic respiration.
Exam cue: In respirometry, account for gas volume, temperature, pressure and absorption of carbon dioxide.
Risk pitfalls and guardrails
Saying oxygen is used directly in glycolysis.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Equating respiration with breathing or gas exchange.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Assuming all organisms produce lactate during anaerobic respiration.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Memory anchors
Glycolysis
Glycolysis converts glucose to pyruvate in the cytoplasm with a small ATP yield.
Link Reaction
Pyruvate is decarboxylated and oxidised to form acetyl coenzyme A.
Krebs Cycle
The Krebs cycle releases carbon dioxide and produces reduced coenzymes and ATP.
Oxidative Phosphorylation
Electron transfer creates a proton gradient that drives ATP synthase.
Respiratory Quotient
Respiratory quotient is carbon dioxide produced divided by oxygen consumed.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A cell extract produces pyruvate from glucose even after mitochondria are removed. In which cellular location do the enzymes responsible normally act?
What is a key outcome of glycolysis?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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