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Contains the answers

Answers · Homeostasis

Homeostasis — return questions key

Check meaning, not exact wording. These are teaching points, not official Cambridge marks.

1. WR1 · Return

Model answer. Homeostasis is the maintenance of a constant internal environment, keeping conditions such as the core temperature close to a set point.

A full answer includes

  • The maintenance of a constant internal environment.

Also accept

  • maintenance of a constant internal environment

Watch for

  • “Keeping the body at the same temperature as its surroundings.” — The surroundings change a lot; homeostasis keeps the inside of the body steady.

2. WR2 · Return

Model answer. (a) The arterioles narrow (vasoconstriction), so less blood flows near the surface and less heat is lost. (b) The muscles shiver, and respiration releases heat.

A full answer includes

  • (a) They narrow (vasoconstriction).
  • (b) They shiver: contract quickly, releasing heat.

Also accept

  • (a) narrow; (b) shiver

Watch for

  • “(a) They widen to carry more warm blood to the skin.” — Widening would lose more heat. In the cold they narrow.

3. WR3 · Return

Model answer. The arterioles supplying the surface capillaries widen (vasodilation), so more heat is lost; sweat glands release sweat, which cools the skin as it evaporates.

A full answer includes

  • The arterioles supplying the skin surface capillaries widen (vasodilation).
  • Sweat glands release sweat, which evaporates.

Also accept

  • vasodilation; sweating

Watch for

  • “The hairs stand up to let heat out.” — Raised hairs are a response to cold. In the warm the hairs lie flat.

4. FR1 · Return

Model answer. The seven parts are the hairs, hair erector muscles, sweat glands, receptors, sensory neurones, blood vessels and fatty tissue.

A full answer includes

  • Any four of: hair; hair erector muscle; sweat gland; receptor; sensory neurone; blood vessels; fatty tissue.

Also accept

  • any four of the seven

Watch for

  • “Bones.” — Bones are not part of the skin.

5. FR2 · Return

Model answer. In negative feedback a condition changes away from its set point; receptors detect the change; the brain coordinates and the effectors respond so that the change is reversed and the condition returns towards the set point.

A full answer includes

  • A condition changes away from its set point.
  • Receptors detect the change.
  • Effectors respond so that the change is reversed and the condition returns to the set point.

Also accept

  • change from set point; receptors detect; effectors reverse it

Watch for

  • “Negative feedback makes the change bigger.” — That would be the opposite. Negative feedback reverses the change.

6. GR1 · Return

Model answer. (a) The pancreas secretes insulin. (b) Insulin decreases the blood glucose concentration.

A full answer includes

  • (a) The pancreas.
  • (b) It decreases it.

Also accept

  • (a) pancreas; (b) decreases

Watch for

  • “(a) The liver.” — The liver responds to insulin; the pancreas secretes it.

7. GR2 · Return

Model answer. (a) Glucagon, secreted by the pancreas. (b) Glycogen, which the liver breaks down into glucose and releases into the blood.

A full answer includes

  • (a) Glucagon.
  • (b) Glycogen.

Also accept

  • (a) glucagon; (b) glycogen

Watch for

  • “(a) Glycogen.” — Glycogen is the store in the liver. The hormone is glucagon.

8. GR3 · Return

Model answer. Type 1 diabetes is treated by measuring the blood glucose concentration regularly, injecting insulin, and planning meals and exercise around it.

A full answer includes

  • Measure the blood glucose concentration.
  • Inject insulin.
  • Plan meals and exercise around the insulin.

Also accept

  • measure; inject insulin; plan meals and exercise

Watch for

  • “Taking glucose tablets every day.” — The treatment replaces the missing hormone: insulin is injected.