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Course: SQA National 5 Biology
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SQA National 5 Biology

1. Unit 1 — Cell Biology

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2. Unit 2 — Multicellular Organisms

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3. Unit 3 — Life on Earth

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Text lesson

1.6.5 Comparing Aerobic Respiration and Fermentation

1.6.5 Comparing Aerobic Respiration and Fermentation: Compare aerobic respiration with fermentation in animals and in yeast and plants, using reactants, products, energy released and location.

1.6.5 Comparing Aerobic Respiration and Fermentation
Oxygen
  • Needs oxygen, so it can only continue if the oxygen supply keeps up.
Products
  • Carbon dioxide and water are produced.
Energy
  • A large amount of energy is released from each glucose molecule.
Location
  • The early steps occur in the cytoplasm and the later steps in the mitochondria.
Oxygen debt idea
  • After exercise the body breathes harder to supply the extra oxygen needed to remove lactic acid built up earlier.
Fermentation
No oxygen
  • Occurs without oxygen, so it can continue in low-oxygen conditions.
Animal products
  • Lactic acid is produced and no carbon dioxide.
Plant and yeast products
  • Ethanol and carbon dioxide are produced.
Energy
  • Only a small amount of energy is released from each glucose molecule.
Where it matters
  • Muscle cells switch to fermentation briefly when the oxygen supply cannot meet demand, but cannot keep this up for long periods.
Why the difference
  • In fermentation the glucose is not fully broken down, so much of the stored energy remains in lactic acid or ethanol.
Short-term use
  • Fermentation provides a quick extra supply of energy in muscles during sprints.
Long-term use
  • Aerobic respiration is the sustainable method used for most of a cell's energy needs.
Feature Aerobic respiration Fermentation (animal) Fermentation (yeast/plant)
Oxygen needed Yes No No
Products CO₂ + H₂O Lactic acid Ethanol + CO₂
Energy released Large Small Small
Location Cytoplasm and mitochondria Cytoplasm Cytoplasm

1.6.5 – Key Points for the Exam

  • Aerobic: With oxygen.
  • Anaerobic: Without oxygen.
  • Lactic acid: Product of fermentation in animal cells.
  • Ethanol: Product of fermentation in yeast and plant cells.

Common Mistakes

  • Stating that fermentation makes more energy than aerobic respiration.
  • Mixing up the products of the two types of fermentation.
  • Claiming that aerobic respiration makes only carbon dioxide; it also makes water.
  • Saying fermentation never happens in humans; muscle cells use it during strenuous exercise.
YOUR STUDY PATH

1.6.5 Comparing Aerobic Respiration and Fermentation

SQA National 5 Biology / 1. Unit 1 — Cell Biology

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