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S4 Biology: Cellular Respiration Paper 4 (Mixed Calculations)
S4 Biology: Cellular Respiration Paper 4 (Mixed Calculations)
This closing paper puts ATP yield, mole conversions, respiratory quotient and efficiency together. Write the formula first, then substitute.
Quick answer 1. 36 ATP (2/2/32) | 2. 6 O2, 6 CO2, 6 H2O | 3. 2 ethanol + 2 CO2 | 4. lactate and oxygen debt | 5. 60 cm3 | 6. RQ 0.83, carbohydrate | 7. 38.3% | 8. +300% | 9. about 1.5 g | 10. 2 ATP, 18 times
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | 25 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S4 Biology — Cellular Respiration |
| Level | Challenge |
02 Questions (10 items)
- FoundationHow many ATP are gained net from complete oxidation of one glucose molecule, and how much does each stage contribute?
- FoundationComplete oxidation of one glucose molecule needs how many oxygen molecules, and releases how many carbon dioxide and water molecules?
- FoundationWhat does yeast produce when it breaks down one glucose molecule without oxygen, and how many molecules of each?
- FoundationDuring hard exercise with too little oxygen, what does glucose become, and why does breathing stay heavy afterwards?
- IntermediateComplete oxidation of 0.45 g glucose releases what volume of carbon dioxide at room temperature? (molar volume 24 dm3, C6H12O6 = 180)
- IntermediateA tissue uses 6.0 mol of oxygen and releases 5.0 mol of carbon dioxide per minute. What is its respiratory quotient and what fuel dominates?
- IntermediateComplete oxidation of one glucose releases 2 870 kJ and each ATP stores 30.5 kJ. What is the storage efficiency?
- ChallengeAn athlete raises oxygen uptake from 0.25 dm3 to 1.00 dm3 per minute. By what percentage does it rise?
- Challenge200 cm3 of carbon dioxide is collected at room temperature from complete oxidation of glucose. What mass of glucose was used at least?
- Error redoA student claims anaerobic fermentation of one glucose nets 36 ATP. What is correct, and how many times larger is the aerobic yield?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Net gain is 36 ATP: 2 from glycolysis, 2 from the Krebs cycle and 32 from oxidative phosphorylation. | Substrate-level phosphorylation gives only four; the rest comes from hydrogen passing down the chain. |
| 2 | It needs 6 oxygen molecules and releases 6 carbon dioxide and 6 water molecules. | Atoms must balance on both sides, so the coefficient stays at six, never twelve. |
| 3 | It produces 2 ethanol molecules and 2 carbon dioxide molecules. | Alcoholic fermentation stops two steps after glycolysis, so most energy stays in the ethanol. |
| 4 | Glucose becomes lactate; extra oxygen is taken in afterwards to oxidise it, and that extra amount is the oxygen debt. | Lactate is carried to the liver, which is why deep breathing continues after a sprint. |
| 5 | 0.45 g is 0.0025 mol, so 0.0025 x 24 dm3 = 0.060 dm3, that is 60 cm3. | Find moles from mass, multiply by molar volume, then convert dm3 into cm3. |
| 6 | RQ = 5.0 / 6.0 = 0.83, close to 1, so carbohydrate is the main fuel. | Fat gives an RQ near 0.7, so closer to 1 means more carbohydrate. |
| 7 | 36 x 30.5 = 1 098 kJ, and 1 098 / 2 870 = 38.3%. | The rest leaves as heat, which is why exercise raises body temperature. |
| 8 | (1.00 – 0.25) / 0.25 x 100% = 300%, a rise of 300%. | The rise is divided by the original value, not the new one. |
| 9 | 200 / 24 000 = 0.00833 mol, so mass = 0.00833 x 180 = about 1.50 g. | Each glucose gives six carbon dioxide molecules, and that ratio is already inside the mole conversion. |
| 10 | Only 2 ATP is correct; 36 / 2 = 18 times more aerobically, because hydrogen has no chain to run down without oxygen. | Mixing the aerobic total with the glycolytic net gain is the commonest error. |
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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