Skip to content
MarkSchemeMarkScheme
Sign up — no card

9700 · 12.2

Respiration — practice questions

Practice and worked examples for 9700 Respiration. Short previews only — attempt the full question in MarkScheme against the official scheme.

Worked example 1

Calculate the theoretical maximum ATP yield from the complete aerobic respiration of one molecule of glucose. Assume that each reduced NAD yields 2.5 ATP and each reduced FAD yields 1.5 ATP.

Show solution outline
  1. Glycolysis:
    • Net ATP from substrate-level phosphorylation: 2 ATP
    • Reduced coenzymes: 2 reduced NAD
  2. Link Reaction (x2 for one glucose):
    • Reduced coenzymes: 2 reduced NAD
  3. Krebs Cycle (x2 for one glucose):
    • ATP from substrate-level phosphorylation: 2 ATP
    • Reduced coenzymes: 6 reduced NAD + 2 reduced FAD
  4. Total reduced coenzymes for Oxidative Phosphorylation:
    • Total reduced NAD = 2 (glycolysis) + 2 (link) + 6 (Krebs) = 10 reduced NAD
    • Total reduced FAD = 2 reduced FAD (from Krebs)
  5. ATP from Oxidative Phosphorylation:
    • From 10 reduced NAD: $10 \times 2.5 = 25ATP ATP
    • From 2 reduced FAD: $2 \times 1.5 = 3ATP ATP
    • Total from oxidative phosphorylation = $25 + 3 = 28ATP ATP
  6. Total ATP Yield:
    • Sum of ATP from all stages = ATP (substrate-level) + ATP (oxidative phosphorylation)
    • Total = (2 ATP from glycolysis + 2 ATP from Krebs) + 28 ATP
    • Final Answer: 32 ATP

Worked example 2

The equation for the aerobic respiration of the lipid tripalmitin is: $2C_{51}H_{98}O_6 + 145O_2 \rightarrow 102CO_2 + 98H_2O$. Calculate the respiratory quotient (RQ) for tripalmitin.

Show solution outline
  1. Identify the formula for RQ: RQ=Volume of CO2 producedVolume of O2 consumedRQ = \frac{\text{Volume of } CO_2 \text{ produced}}{\text{Volume of } O_2 \text{ consumed}}
  2. Use the stoichiometry of the balanced chemical equation: According to Avogadro's Law, the molar ratio of gases is equivalent to their volume ratio under the same conditions.
  3. Extract the molar coefficients for CO₂ and O₂:
    • Moles of CO₂ produced = 102
    • Moles of O₂ consumed = 145
  4. Calculate the RQ: RQ=102145RQ = \frac{102}{145}
  5. Final Answer: RQ≈0.70RQ \approx 0.70. This value is less than 1.0 and is characteristic of lipid respiration, reflecting the higher hydrogen-to-oxygen ratio in the molecule compared to carbohydrates.
Mark a 9700 question on this topicFull lessonOpen in course studio