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S5 Biology: Homeostasis (Paper 1)
S5 Biology: Homeostasis (Paper 1)
The first paper builds the conceptual frame: the definition, the three parts of negative feedback, the contrast with positive feedback, and normal ranges for temperature and blood glucose.
Direct answer Homeostasis holds the internal environment within narrow limits; negative feedback uses a receptor, coordination centre and effector whose response opposes the change; only positive feedback amplifies it.
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: Homeostasis |
| Level | Four basic, three advanced, two challenge and one error-repair item |
02 Questions (10 items)
- FoundationWhat is homeostasis?
- FoundationWhich three parts make up a negative feedback mechanism?
- FoundationGive one example of negative feedback.
- FoundationWhy must body temperature be kept stable?
- IntermediateHow does positive feedback differ from negative feedback?
- IntermediateNormal body temperature is 37 °C. What is a rise of 2 °C, and what does it indicate?
- IntermediateWhat is the normal fasting blood glucose range?
- ChallengeBody temperature falls from 39.0 °C to 37.5 °C after sweating. How much did it fall, and which feedback is this?
- ChallengeA diabetic patient has a blood glucose of 12 mmol/dm³ against an upper limit of 8. How far above the limit is that?
- Error redoA student says negative feedback makes a change grow larger. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Keeping the internal environment, such as temperature, blood glucose, water and pH, within narrow limits despite outside changes | Stability is achieved by constant small adjustments rather than by a fixed, unchanging state. |
| 2 | Receptor, coordination centre and effector | A receptor detects the change, a coordination centre compares it with the set point, and an effector responds to restore it. |
| 3 | A rise in body temperature increases sweating, which brings the temperature back down | Sweating removes heat, so once temperature falls sweating slows, which makes the loop self-limiting. |
| 4 | Enzymes work best at an optimum temperature; a shift slows metabolism and excess heat denatures them | Metabolism depends on enzymes, and once denatured they cannot recover, so temperature control is a matter of survival. |
| 5 | Negative feedback reverses a change; positive feedback amplifies it, as in uterine contractions during birth | Positive feedback is rare and is used for processes that must be completed quickly. |
| 6 | 39 °C, which counts as a fever | Thirty-seven plus two gives 39 °C, above the normal range and usually a sign of infection. |
| 7 | About 4 to 6 mmol/dm³, and usually below 8 mmol/dm³ after a meal | Insulin and glucagon act together to hold blood glucose inside this range. |
| 8 | A fall of 1.5 °C, which is negative feedback | Thirty-nine minus 37.5 gives 1.5, and the cooling is pulling the raised value back towards the set point. |
| 9 | 4 mmol/dm³ above the limit | Twelve minus eight gives four, which is half as much again as the upper limit. |
| 10 | Negative feedback opposes the change and restores the set point; it is positive feedback that amplifies it | Confusing the two is the commonest lost mark; remember that negative means the response opposes the change. |
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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