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12.3Respiration

Anaerobic respiration — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

5 min read 9 parts Lesson 4 of 4 1 quiz

📚 Cambridge IGCSE Biology 0610 Hub / Topical Revision
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Lesson summary

12.3 Anaerobic respiration — IGCSE BIOLOGY notes: Describe anaerobic respiration in muscles and yeast, its equations and the oxygen debt.Anaerobic respiration = the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.Incomplete br…

  • Incomplete breakdown
  • No carbon dioxide
  • Bread making
  • Lactic acid build-up
  • Repaying the debt
  • Fermentation

Part 1 of 7Definition

Anaerobic respiration
Anaerobic respiration the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.
Incomplete breakdown
  • Glucose is only partly broken down.
Energy
  • A relatively small amount of energy is released compared with aerobic respiration.
Products
  • They differ with the type of organism.

Part 2 of 7Anaerobic respiration in animals

Where
  • Mainly in muscle cells during vigorous exercise.
Why
  • Oxygen cannot be delivered fast enough for aerobic respiration, so some glucose is broken down without oxygen.
Equation
  • Equation glucose → lactic acid.
Energy
  • Energy remains in the bonds of lactic acid, so less is released.
No carbon dioxide
  • Lactic acid is the only product in animals.

Part 3 of 7Anaerobic respiration in yeast

Equation
  • Equation glucose → alcohol + carbon dioxide.
Bread making
  • The carbon dioxide makes dough rise.
Brewing
  • Ethanol gives the beer its alcohol and carbon dioxide gives it fizz.

Part 4 of 7Balanced equation in yeast (Supplement)

Equation
  • C6H12O6 → 2C2H5OH + 2CO2.
Products
  • One glucose molecule gives two ethanol molecules and two carbon dioxide molecules.

Part 5 of 7Oxygen debt (Supplement)

Lactic acid build-up
  • Lactic acid accumulates in muscle cells and lowers their pH, which could denature enzymes.
Removal
  • Cells excrete it into the blood and it is taken to the liver.
Oxidation
  • In liver cells lactic acid reacts with oxygen to form carbon dioxide and water.
Repaying the debt
  • Fast heart rate and deep, fast breathing continue to carry lactic acid to the liver and supply oxygen.

Part 6 of 7Aerobic and anaerobic compared

FeatureAerobicAnaerobic
OxygenNeededNot needed
Glucose breakdownCompleteIncomplete
Energy per glucoseRelatively largeRelatively small
Products in animalsCarbon dioxide and waterLactic acid
Products in yeastCarbon dioxide and waterEthanol and carbon dioxide

Part 7 of 7More from the specification

More from the specification
Alcoholic Fermentation in Yeast Suspensions
  • Yeast cells respiring anaerobically metabolise glucose into ethanol and carbon dioxide gas, a reaction widely harnessed in brewing and bread-making industries.
Decolourisation Time versus Rate of Reaction
  • In methylene blue indicator experiments, a shorter time for the colour change corresponds to a higher metabolic rate of respiration.
    • (Rate = 1 / Time)
Lactic Acid Accumulation and Oxygen Debt
  • Rapid anaerobic respiration in skeletal muscles produces lactic acid,
  • which lowers cellular pH and requires subsequent aerobic oxidation in the liver to repay the oxygen debt.
Independent variable
  • The factor deliberately changed in an investigation.
Dependent variable
  • The factor measured to see the effect of the change.

Key terms

TermMeaning
Anaerobic respirationReactions that release energy from nutrients without oxygen.
Lactic acidProduct of anaerobic respiration in animal muscle.
EthanolAlcohol produced by yeast in anaerobic respiration.
FermentationAnaerobic respiration by yeast producing ethanol and carbon dioxide.
Oxygen debtExtra oxygen needed after exercise to oxidise lactic acid.

Avoid these mistakes

1
Saying animals make ethanol anaerobically — animals make lactic acid only.
2
Saying anaerobic respiration releases more energy — it releases much less per glucose.
3
Saying carbon dioxide is made when muscles respire anaerobically — it is not.
4
Saying the oxygen debt is repaid immediately — breathing and heart rate stay raised until lactic acid is removed.

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