Topics

CGP, Oxford, and more
Amazon amazon.co.uk
Microscope Slides
Prepared slides for practicals
Amazon amazon.co.uk
Biology Field Guides
Required practical support
Amazon amazon.co.uk
Fastmail — Private Email
Privacy-first email with no ads and no tracking
fastmail.com
Dynadot — Domain Registration →
Register or transfer domains with free SSL and affordable pricing
dynadot.com
Zen Internet — UK Broadband →
Award-winning UK broadband with no data caps and great customer service
zen.co.uk
Biology Revision Guides
A-Level Revise Aid: This resource is designed to support your revision and may contain errors. If you find a discrepancy with your class teaching, your teacher is correct -- please let us know at alevelrevise@scott.scottrix.co.uk.

Biochemistry and Respiration

Year 1 / ASYear 2 / A-Level All Boards (AQA, Edexcel, OCR, WJEC, CCEA) AQA

A-Level Biology revision: Biochemistry and Respiration. Learning objectives, key points, worked examples and practice questions across AQA, Edexcel, OCR, WJEC and CCEA.

Fastmail

📌 Key Points

Key Fact: Glycolysis: glucose -> 2 pyruvate (cytoplasm); net 2 ATP, 2 NADH; Link: pyruvate -> acetyl CoA + CO₂ + NADH (mito matrix); Krebs: acetyl CoA + 3NAD⁺ + FAD + GDP -> 2CO₂ + 3NADH + FADH₂ + GTP; ETC: NADH/FADH₂ -> H⁺ gradient -> ATP synthase -> ATP
Key Fact: SLP: direct phosphate transfer (glycolysis, Krebs); OxPhos: H⁺ pumped across inner membrane, flow through ATP synthase
Key Fact: Theoretical: 10 NADH (2.5 each) + 2 FADH₂ (1.5 each) + 4 ATP = 32 ATP; Actual ~30-32
Key Fact: Anaerobic: animals: pyruvate + NADH -> lactate + NAD⁺ (lactate dehydrogenase); Yeast: pyruvate -> acetaldehyde + CO₂ -> ethanol + NAD⁺
Key Fact: Enzymes: globular proteins, active site, specific; Induced fit: substrate binding changes shape; Factors: temp, pH, [substrate], inhibitors (competitive/non-competitive)
Key Fact: Feedback inhibition: end product inhibits early enzyme; Allosteric: effector binds site != active site, changes conformation

🎯 Learning Objectives

  • Detail glycolysis, link reaction, Krebs cycle, oxidative phosphorylation
  • Explain substrate-level phosphorylation and oxidative phosphorylation (chemiosmosis)
  • Calculate ATP yield per glucose (theoretical vs actual)
  • Describe anaerobic respiration in animals (lactate) and yeast (ethanol)
  • Explain enzyme structure, mechanism (lock-and-key, induced fit), factors affecting activity
  • Understand metabolic pathways regulation: feedback inhibition, allosteric regulation

💡 Worked Example

Exam-Style Question

Question: Calculate total ATP from one glucose via aerobic respiration. Explain why yield is often less than theoretical

Model Answer:

Glycolysis: 2 ATP + 2 NADH (3-5 ATP); Link: 2 NADH (5 ATP); Krebs: 2 ATP + 6 NADH (15 ATP) + 2 FADH₂ (3 ATP) = 25-30 + 4 = 29-32 ATP. Less because: proton leak, shuttle costs (glycerol-3-P shuttle vs malate-aspartate), ATP for transport

❓ Practice Questions

Questions:

  • Where does each stage of respiration occur?
  • Why does anaerobic respiration produce less ATP?
  • Explain induced fit model
  • How does cyanide affect respiration?

🎬 Video Resources

📄 Past Papers & Exam Resources

🔗 Further Reading & Resources