1[2 marks]
Explain why it is important for the body to maintain a constant internal environment when conditions outside the body change.
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- enzymes work best at their optimum conditions / within narrow limits (1)
- so cells can function properly / reactions continue at a suitable rate (1)
2
Triple only
[3 marks]Explain why core body temperature must not rise far above 37°C.
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- high temperature denatures enzymes / changes the shape of the active site (1)
- the substrate no longer fits the active site (1)
- so reactions in the cells slow down or stop (1)
3
Triple only
[2 marks]A person drinks a large amount of water and the blood becomes too dilute. Explain the effect this could have on animal cells.
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- water enters the cells by osmosis (1)
- the cells swell and may burst (1)
4
Triple only
[3 marks]Describe the roles of the hypothalamus and the dermis in controlling body temperature.
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- the hypothalamus monitors blood temperature / receives impulses from skin temperature receptors (1)
- the hypothalamus coordinates the response / sends nerve impulses to effectors (1)
- the dermis contains the sweat glands / blood vessels / temperature receptors (1)
5
Triple onlyHigher tier
[6 marks]A person walks from a warm building into very cold air. Explain how the body responds to keep core body temperature constant.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | A detailed explanation that links detection by the hypothalamus to at least two responses, including shivering and vasoconstriction, and explains how each helps keep body temperature constant. |
| 2 | 3–4 | Some explanation with at least one response linked to its effect on body temperature. Detection or a second response may be missing or incomplete. |
| 1 | 1–2 | Simple statements about the body responding to cold, with little or no explanation. |
Indicative content
- temperature receptors in the skin and the hypothalamus detect the fall in temperature
- the hypothalamus sends nerve impulses to effectors
- shivering: muscles contract rapidly
- respiration in the muscles releases heat, warming the body
- vasoconstriction: blood vessels supplying the skin surface narrow
- less blood flows near the skin surface so less heat is lost
- sweating is reduced
- temperature returns to about 37°C, which is negative feedback