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S5 Biology: Respiration (Paper 3)
S5 Biology: Respiration (Paper 3)
The third paper links respiration to applications and whole-body metabolism: exercise, brewing, energy budgeting, ventilation and inhibitors.
Direct answer Anaerobic respiration is an emergency supply that still needs oxygen to clear lactate; oxygen is the final electron acceptor; fat holds over twice the energy per gram of carbohydrate; ventilation equals rate times tidal volume.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S5 Biology: Respiration |
| Level | Four basic, three advanced, two challenge and one error-repair item |
02 Questions (10 items)
- FoundationWhy do muscles switch to anaerobic respiration during hard exercise?
- FoundationWhy is yeast kept without oxygen when brewing?
- FoundationWhat is the final electron acceptor of the electron transport chain?
- FoundationHow much of the energy released by respiration is captured as ATP, and where does the rest go?
- IntermediateA person uses 60 dm³ of oxygen in 30 minutes. What is the average oxygen uptake per minute?
- IntermediateRespiration doubles from 20 °C to 30 °C but falls sharply at 40 °C. Explain.
- IntermediateFat gives about 39 kJ/g and carbohydrate about 17 kJ/g. How much more energy do 5 g of fat release than 5 g of carbohydrate?
- ChallengeBreathing rate rises from 12 to 24 per minute with each breath still 500 cm³. How does minute ventilation change?
- ChallengeCyanide blocks the electron transport chain. Why do cells die even when blood oxygen is normal?
- Error redoA student says respiration happens only in the lungs. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Oxygen supply cannot keep up, so anaerobic respiration provides ATP immediately | Anaerobic respiration is fast and needs no oxygen, but lactate builds up and limits how long it can continue. |
| 2 | Without oxygen it carries out alcohol fermentation, producing ethanol and carbon dioxide | With oxygen, yeast oxidises sugar completely to carbon dioxide and water, giving no ethanol. |
| 3 | Oxygen, which is reduced to water | Oxygen is reduced to water, so without it the whole chain stalls. |
| 4 | Only part is captured as ATP and the rest is lost as heat | This explains the rise in body temperature during exercise and why food energy is not all usable ATP. |
| 5 | 2 dm³ per minute, that is 2 000 cm³ | Sixty divided by thirty gives two, and one cubic decimetre is one thousand cubic centimetres. |
| 6 | Up to the optimum the enzymes speed up, but beyond it they denature irreversibly | Denaturation is irreversible, so cooling down does not restore the rate at once. |
| 7 | 110 kJ more, that is 195 kJ against 85 kJ | Five grams of fat gives 195 kJ and five grams of carbohydrate 85 kJ, a difference of 110 kJ. |
| 8 | It doubles from 6 000 cm³ to 12 000 cm³ | Twelve times five hundred is six thousand and twenty-four times five hundred is twelve thousand. |
| 9 | The chain stalls, oxidative phosphorylation stops and ATP runs out | Oxygen is present but unusable, so cells are effectively stuck in an anaerobic state. |
| 10 | Every living cell respires in its cytoplasm and mitochondria, while the lungs only exchange gases | The lungs only exchange gases; oxygen must be carried by blood to the cells that respire. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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