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12.2.912 · Energy and Respiration

Energy Yield- Aerobic and Anaerobic Respiration — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 9 parts Lesson 15 of 18 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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12.2.9 Energy Yield: Aerobic and Anaerobic Respiration — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Compare the ATP yield of aerobic and anaerobic respiration and explain why the yield differs.Glycolysis — 2 ATP net by substrate-level phosphorylation and 2 reduce…

  • Link reaction
  • Krebs cycle
  • Oxidative phosphorylation
  • Reduced NAD
  • Reduced FAD
  • Direct ATP

Part 1 of 7ATP made at each stage of aerobic respiration

1Glycolysis
  • 2 ATP net by substrate-level phosphorylation and 2 reduced NAD.
2Link reaction
  • Link reaction no ATP, 2 reduced NAD.
    • (one per pyruvate)
3Krebs cycle
  • 2 ATP by substrate-level phosphorylation, 6 reduced NAD and 2 reduced FAD.
4Doubling
  • Doubling every figure for the link reaction and Krebs cycle is doubled because one glucose gives two pyruvate.
StageDirect ATPReduced NADReduced FAD
Glycolysis2 (net)20
Link reaction020
Krebs cycle262
Total4102

Part 2 of 7Two types of ATP synthesis

Substrate-level phosphorylation
  • Substrate-level phosphorylation a phosphate is transferred directly from a substrate to ADP.
  • Where
    • in the cytoplasm and the mitochondrial matrix.
  • Yield
    • only about 4 ATP per glucose.
Oxidative phosphorylation
  • ATP made by chemiosmosis using energy from the electron transport chain.
  • Where
    • across the inner mitochondrial membrane.
  • Yield
    • most of the ATP, about 26 to 30 per glucose.
Oxygen
  • Oxygen the final electron acceptor, forming water.

Part 3 of 7Calculating the total yield

Reduced NAD
  • Reduced NAD about 2.5 ATP each by oxidative phosphorylation.
  • 10 reduced NAD give about 25 ATP.
Reduced FAD
  • Reduced FAD about 1.5 ATP each.
  • 2 reduced FAD give about 3 ATP.
Direct ATP
  • 4 ATP from substrate-level phosphorylation.
Maximum total
  • Maximum total about 32 ATP per glucose.
  • Older sources use 3 and 2 ATP per reduced NAD and FAD, giving about 38.
Realistic total
  • Realistic total about 30 ATP because ATP is used to move pyruvate, phosphate and reduced NAD into the mitochondria.
  • Cambridge notes quote roughly 30 to 36, so state the assumptions used.

Part 4 of 7Why the actual yield is lower than the maximum

Proton leak
  • Proton leak some protons cross the inner membrane without passing through ATP synthase.
Transport costs
  • Transport costs energy is used to move ADP, phosphate and pyruvate into the matrix.
Non-integer ratio
  • Non-integer ratio the number of protons pumped per reduced NAD and per ATP is not a whole number.
Heat
  • Heat some energy is released as heat, which is useful in endotherms.
Biosynthesis
  • Krebs cycle intermediates may be withdrawn to make other molecules.

Part 5 of 7Anaerobic respiration yield

1Only glycolysis makes ATP
  • Only glycolysis makes ATP net 2 ATP per glucose in both lactate and ethanol fermentation.
2No oxidative phosphorylation
  • No oxidative phosphorylation reduced NAD is re-oxidised in the fermentation step instead of the electron transport chain.
3Incomplete oxidation
  • Incomplete oxidation glucose is only partially oxidised, so lactate or ethanol keeps most of the chemical energy.
4Mitochondrial stages stop
  • Mitochondrial stages stop with no oxygen as the final electron acceptor, the link reaction, Krebs cycle and electron transport chain cannot run.

Part 6 of 7Aerobic compared with anaerobic

FeatureAerobicAnaerobic
StagesGlycolysis, link reaction, Krebs cycle, oxidative phosphorylationGlycolysis and fermentation
LocationCytoplasm and mitochondriaCytoplasm only
ATP per glucoseAbout 30 to 36 (high)2 (low)
Oxidation of glucoseCompleteIncomplete
ProductsCO2 and H2OLactate (mammals) or ethanol and CO2 (yeast, plants)
Oxygen neededYesNo
EfficiencyAbout 30 to 40 %About 2 to 3 %

Part 7 of 7Efficiency of energy transfer

1Efficiency
  • Efficiency energy transferred to ATP as a percentage of the energy in the glucose.
2Energy per ATP
  • Energy per ATP about 30.5 kJ per mole of ATP made.
3Energy in glucose
  • Energy in glucose about 2880 kJ per mole.
4Consequence
  • Consequence an organism relying on anaerobic respiration needs far more glucose for the same ATP,
    • so only short bursts or tolerant organisms rely on it.

Key terms

TermMeaning
Net yieldATP made minus ATP used.
Substrate-level phosphorylationDirect transfer of a phosphate from an intermediate to ADP.
Oxidative phosphorylationATP formation using energy from the electron transport chain.
Proton leakMovement of protons across the inner membrane without passing through ATP synthase.
Complete oxidationBreakdown of a substrate to CO2 and H2O.
EfficiencyProportion of the energy released that is transferred to ATP.

Avoid these mistakes

1
Quoting 38 ATP without qualification — real yields are lower, about 30, because of proton leak and transport costs.
2
Saying fermentation makes ATP — the 2 ATP are made in glycolysis; fermentation only regenerates NAD.
3
Leaving out the 2 ATP made by substrate-level phosphorylation in the Krebs cycle — they must be included.
4
Forgetting to double link reaction and Krebs cycle figures — one glucose gives two pyruvate.

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