Question 1
Paper 1A style
Why is negative feedback, not positive feedback, used in homeostasis?
- It amplifies changes so that the response is faster.
- It returns a variable to the set point from values above and below it.
- It keeps a variable exactly at the set point without any fluctuation.
- It only works when a variable rises above the set point.
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Answer: B [1]
Question 2
Paper 1A style
Which is an effect of glucagon on its target cells?
- Muscle cells insert more glucose transporters into their membranes.
- Liver cells convert glucose to glycogen.
- Liver cells break down glycogen and release glucose into the blood.
- β cells increase their secretion of insulin.
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Answer: C [1]
Question 3
Paper 1B style
Two adults each drank a solution containing 75 g of glucose after fasting overnight. Their blood glucose concentration was then measured every 30 minutes (data for practice). (a) Calculate the percentage increase in blood glucose for person A between 0 and 30 minutes. [1] (b) Describe the changes in blood glucose for person A. [2] (c) Person B has type 2 diabetes. Explain the differences between the results for B and A. [2]
| Time (min) | Person A | Person B |
|---|---|---|
| 0 | 5.0 | 7.5 |
| 30 | 8.0 | 12.5 |
| 60 | 6.5 | 14.0 |
| 90 | 5.5 | 13.0 |
| 120 | 5.0 | 11.5 |
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- (a) (8.0 − 5.0) ÷ 5.0 × 100 = 60% [1]
- (b) rises to a peak (8.0 mmol L⁻¹) at 30 minutes [1]
- (b) then falls back to the starting value / 5.0 mmol L⁻¹ by 120 minutes [1]
- (c) B starts higher / rises higher / stays high (above 11 mmol L⁻¹ at 120 min) [1]
- (c) B's target cells are resistant / less responsive to insulin [1]
- (c) so liver / muscle cells absorb less glucose / convert less to glycogen [1]
- (c) A secretes insulin which returns glucose to the set point by negative feedback [1]
- [max 5]
Question 4
Paper 2A style
Outline two risk factors for type 2 diabetes and one method of treatment.
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- obesity / high body mass [1]
- physical inactivity / lack of exercise [1]
- diet high in sugar / fat / refined carbohydrates [1]
- increasing age / family history / genetic factors / ethnicity [1]
- treatment: low-sugar diet / regular exercise / weight loss / drugs that improve insulin sensitivity / insulin injections [1]
- [max 3: max 2 for risk factors]
Question 5
Paper 2B style
Explain how the body temperature of a human is returned to normal after exposure to cold conditions.
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- negative feedback control [1]
- peripheral thermoreceptors in the skin detect the fall in temperature [1]
- hypothalamus detects / compares with the set point (about 37 °C) [1]
- hypothalamus sends nerve impulses to effectors [1]
- vasoconstriction of arterioles supplying skin capillaries [1]
- less blood near the surface so less heat lost (by radiation) [1]
- shivering: rapid contractions of skeletal muscle generate heat from respiration [1]
- uncoupled respiration in brown adipose tissue releases heat instead of producing ATP [1]
- hair erection traps an insulating layer of air [1]
- hypothalamus stimulates the pituitary (TSH) to increase thyroxin secretion [1]
- thyroxin raises the metabolic rate so more heat is generated [1]
- sweating reduced / stops [1]
- behavioural responses, e.g. putting on clothes / seeking warmth [1]
- [max 7]