GCSERevise
AQASpec 4.4.2Foundation & Higher~25 min

Respiration

Biology · Topic revision workspace

Topic progress0%

Read the notes, score 80% and know 75% of the cards.

Topic overview

What you need to know

Respiration is a key part of GCSE Biology. Connect structures to their functions and explain biological processes as clear causal sequences. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy). Glucose + oxygen → carbon dioxide + water + energy. Glucose → lactic acid (+ small amount of energy). Occurs without oxygen, e.g. during intense exercise. Glucose → ethanol + carbon dioxide (+ small amount of energy). Also called fermentation.

Exam tip

Use precise scientific vocabulary and make each link in an explanation explicit.

Revision notes

Core ideas

Secure these ideas first. Say each definition in your own words, then connect it to the topic overview.

  • Aerobic Respiration Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy). Glucose + oxygen → carbon dioxide + water + energy.
  • Anaerobic Respiration (Animals): Glucose → lactic acid (+ small amount of energy). Occurs without oxygen, e.g. during intense exercise.
  • Anaerobic Respiration (Plants/Yeast): Glucose → ethanol + carbon dioxide (+ small amount of energy). Also called fermentation.
  • Exothermic Reaction: A reaction that releases energy to the surroundings. Respiration is exothermic — it transfers energy.

Revision notes

Apply it in the exam

The exam will rarely ask for an isolated definition. Practise selecting the right idea and using it as part of a complete explanation or method.

  • Mitochondria: The organelle where aerobic respiration occurs. Has a folded inner membrane to increase surface area for reactions.
  • Oxygen Debt: The extra oxygen needed after anaerobic exercise to break down the accumulated lactic acid.
  • Fermentation: Anaerobic respiration in yeast: glucose → ethanol + CO₂. Used in brewing and bread-making.
  • Metabolism: The sum of all chemical reactions in an organism. Includes both building up (anabolic) and breaking down (catabolic) reactions.

Core knowledge

Key facts for Respiration

1

Aerobic Respiration Equation

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy). Glucose + oxygen → carbon dioxide + water + energy.

2

Anaerobic Respiration (Animals)

Glucose → lactic acid (+ small amount of energy). Occurs without oxygen, e.g. during intense exercise.

3

Anaerobic Respiration (Plants/Yeast)

Glucose → ethanol + carbon dioxide (+ small amount of energy). Also called fermentation.

4

Exothermic Reaction

A reaction that releases energy to the surroundings. Respiration is exothermic — it transfers energy.

5

Mitochondria

The organelle where aerobic respiration occurs. Has a folded inner membrane to increase surface area for reactions.

6

Oxygen Debt

The extra oxygen needed after anaerobic exercise to break down the accumulated lactic acid.

7

Fermentation

Anaerobic respiration in yeast: glucose → ethanol + CO₂. Used in brewing and bread-making.

8

Metabolism

The sum of all chemical reactions in an organism. Includes both building up (anabolic) and breaking down (catabolic) reactions.

Active recall

Close the notes and answer these

  1. 1.Without looking, explain aerobic respiration equation and give one example or consequence.
  2. 2.Without looking, explain anaerobic respiration (animals) and give one example or consequence.
  3. 3.Without looking, explain anaerobic respiration (plants/yeast) and give one example or consequence.
  4. 4.Without looking, explain exothermic reaction and give one example or consequence.

Content reviewed 23 July 2026 against the current linked specification.

Finished learning?

Mark the notes complete, then test what you can recall.

Previous topicPhotosynthesis
Official AQA specification
Next topicHomeostasis & Response