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S5 Biology: Respiration (Paper 1)
S5 Biology: Respiration (Paper 1)
The first paper builds the framework: the purpose of cellular respiration, where glycolysis happens, the Krebs cycle and mitochondrial structure.
Direct answer Balance the equation carbon first then oxygen; glycolysis gives a net two ATP and two pyruvate without oxygen; the Krebs cycle turns twice per glucose; cristae raise the membrane area.
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)
- FoundationWhat is the main purpose of cellular respiration?
- FoundationIn the equation for complete oxidation of glucose, how many oxygen molecules are used and how many carbon dioxide molecules are released per glucose?
- FoundationWhere does glycolysis happen, and what is the net yield of ATP and pyruvate per glucose?
- FoundationWhat happens when ATP is hydrolysed to ADP and phosphate?
- IntermediateThe Krebs cycle turns twice per glucose. How many NADH are produced in total?
- IntermediateOne glucose yields about 30 ATP aerobically. About how many ATP do three glucose molecules yield?
- IntermediateHow does cellular respiration differ from breathing?
- ChallengeWhich two structural features of a mitochondrion favour aerobic respiration?
- ChallengeHeart muscle cells contain far more mitochondria than ordinary body cells. Suggest why.
- Error redoA student says glycolysis needs oxygen. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | To release chemical energy from food and store it as ATP | Cells cannot use food energy directly, so respiration converts it into ATP. |
| 2 | Six oxygen in, six carbon dioxide out | One glucose needs six oxygen molecules and gives six carbon dioxide molecules, with water as the other product. |
| 3 | In the cytoplasm; a net gain of two ATP and two pyruvate | Glycolysis makes four ATP but spends two at the start, so the net gain is two. |
| 4 | Energy is released for activities such as muscle contraction and active transport | ATP is the immediate energy currency, so its hydrolysis supplies energy straight away. |
| 5 | Six NADH, three per turn | Each turn gives three NADH and glucose drives two turns, giving six in total. |
| 6 | About 90 ATP | Thirty times three gives ninety, so ATP yield rises in proportion to glucose. |
| 7 | Respiration releases energy inside cells, while breathing is the mechanical movement of air | Ventilation only moves oxygen to the lungs and then to cells; the energy release itself happens inside cells. |
| 8 | Cristae fold the inner membrane to hold the electron transport chain, and the matrix holds Krebs cycle enzymes | A larger membrane area carries more electron transport chain, so more ATP can be made. |
| 9 | The heart contracts continuously and needs a large, steady supply of ATP | The greater the ATP demand, the more mitochondria and cristae a cell tends to contain. |
| 10 | Glycolysis needs no oxygen and occurs in the cytoplasm as the shared first stage | Oxygen only acts at the end of the electron transport chain, so glycolysis proceeds with or without it. |
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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