Session XP: 0
B8 · BioenergeticsAQA GCSE Biology · 8461 (Triple)

Respiration — Aerobic & Anaerobic

Aerobic and anaerobic equations, response to exercise, oxygen debt, fermentation. Paper 1 and Paper 2.

Best score
Last attempt
Best attempt progress
0
XP earned
Watch first
CognitoAerobic and anaerobic respiration
MrExhamRespiration — exercise and oxygen debt
Key facts & methods

Aerobic respiration

  • Word equation: glucose + oxygen → carbon dioxide + water
  • Symbol equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
  • Aerobic respiration is an exothermic reaction — releases energy to the environment.
  • Most reactions take place in the mitochondria.
  • Energy released is used for: muscle contraction, maintaining body temperature, active transport, building molecules.

Anaerobic respiration

  • Occurs when oxygen supply is insufficient (e.g. during vigorous exercise).
  • In animals: glucose → lactic acid. Equation: glucose → lactic acid.
  • Lactic acid causes muscle fatigue and soreness.
  • In plants and yeast: glucose → ethanol + carbon dioxide.
  • Yeast fermentation used in brewing (alcohol) and bread making (CO₂ causes rising).
  • Anaerobic respiration releases much less energy than aerobic (incomplete oxidation of glucose).

Response to exercise

  • During exercise: heart rate, breathing rate and breath volume increase.
  • More blood to muscles → more O₂ and glucose delivered, more CO₂ removed.
  • At very high intensity, anaerobic respiration supplements aerobic.
  • Oxygen debt (excess post-exercise oxygen consumption): extra O₂ needed after exercise to oxidise lactic acid.
  • Lactic acid transported in blood to liver where it is converted back to glucose.

Comparing aerobic and anaerobic

  • Aerobic: needs O₂, complete oxidation, high energy yield, CO₂ + H₂O produced.
  • Anaerobic (animals): no O₂, incomplete oxidation, low energy yield, lactic acid produced.
  • Anaerobic (yeast): no O₂, incomplete oxidation, ethanol + CO₂ produced.
  • Both start with glucose. Both release energy. Aerobic releases far more.
  • AQA exam tip: always state where aerobic respiration mainly occurs (mitochondria).
Exam questions — 5 questions · 12 marks · AQA 8461 style
Show all reasoning — the AI marks against the AQA mark scheme. Partial credit for correct biology even if wording differs.
1 markAerobic equationAQA 8461 style

What are the products of aerobic respiration?

A Glucose and oxygen
B Lactic acid
C Carbon dioxide and water
D Ethanol and carbon dioxide
3 marksAnaerobic respirationAQA 8461 P1 style

A student runs a 400 m race. Describe what happens in their muscle cells to release energy when oxygen supply is insufficient, and explain what causes the "burning" sensation in the muscles. (3 marks)

Hint: Name the process, name the product, explain the consequence.
+30 XP
3 marksOxygen debtAQA 8461 style

After a sprint race, an athlete continues to breathe heavily for several minutes. Explain why, in terms of oxygen debt. (3 marks)

Hint: Link to: what was produced during the sprint, what needs to happen to it, why extra O₂ is needed.
+30 XP
4 marksFermentation applicationAQA 8461 style

Yeast is used to make bread. Explain how the metabolic process occurring in the yeast causes the bread to rise. Include the word equation for the relevant reaction. (4 marks)

Hint: Name the type of respiration, write the word equation, and explain how the gas produced causes rising.
+40 XP
1 markComparing respiration typesAQA 8461 style

Which statement correctly compares aerobic and anaerobic respiration in muscle cells?

A Both produce the same amount of energy per glucose molecule
B Aerobic respiration releases more energy and requires oxygen; anaerobic releases less energy and produces lactic acid
C Anaerobic respiration only occurs during rest
D Aerobic respiration produces lactic acid

Module complete! 🎉

Score loading...

+10 XP