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1.6.4Unit 1 — Cell Biology

Fermentation — SQA National 5 Biology Revision Notes & Topical Questions

5 min read 4 parts Lesson 26 of 28

📚 SQA National 5 Biology Hub / Topical Revision
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Part 1 of 4Respiration Without Oxygen

1.6.4 Fermentation
Definition
  • Fermentation releases some energy from glucose when oxygen is not available.
Incomplete
  • Glucose is only partly broken down, so much less energy is released than in aerobic respiration.
Cytoplasm
  • Fermentation takes place in the cytoplasm and does not need mitochondria.
Two types
  • The products differ in animal cells and in plant and yeast cells.
Why it matters
  • Fermentation lets cells keep releasing a little energy for a short time when oxygen is in short supply, such as in a sprinting muscle.

Part 2 of 4Animal Cells

1
During hard exercise, muscle cells cannot get oxygen fast enough to meet their energy demand.
2
Glucose is partly broken down without oxygen, and lactic acid is formed: glucose → lactic acid + a small amount of energy.
3
Lactic acid builds up in the muscles and can cause fatigue and cramp.
4
After exercise extra oxygen is taken in, mainly to break down the lactic acid, which is why breathing stays rapid for a time.

Part 3 of 4Plant and Yeast Cells

Plant and Yeast Cells
Products
  • Glucose → ethanol + carbon dioxide + a small amount of energy.
Brewing
  • Yeast fermentation makes the ethanol in beer and wine.
Baking
  • Carbon dioxide produced by yeast makes bread dough rise.
Plant roots
  • Plant roots in waterlogged soil may ferment, producing ethanol, which damages the plant.
Energy remaining
  • Ethanol still stores a lot of chemical energy, which is why it can be burned as a fuel and why fermentation releases so little.

Part 4 of 4Exam Checklist & Tips

1.6.4 – Key Points for the Exam

  • Fermentation Release of energy from glucose without oxygen.
  • Lactic acid The product of fermentation in animal muscle cells.
  • Ethanol The alcohol produced by fermentation in yeast and plant cells.
  • Fatigue Tiredness of muscles due to lactic acid build-up.

Common Mistakes

  • Saying that fermentation releases no energy; it releases a small amount.
  • Writing that lactic acid is produced by yeast; yeast makes ethanol and carbon dioxide.
  • Stating that humans produce ethanol in muscles.
  • Thinking that fermentation happens in mitochondria; it happens in the cytoplasm.

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