Answers · Homeostasis
Homeostasis — final check key
Check meaning, not exact wording. These are teaching points, not official Cambridge marks.
1. WK1 · Final check
Model answer. Homeostasis is the maintenance of a constant internal environment. The core temperature is part of that environment: it fell by only 0.1 °C and stayed close to its set point of 37 °C, while the skin temperature at the surface fell by 8.5 °C.
A full answer includes
- Homeostasis is the maintenance of a constant internal environment.
- The core temperature (internal environment) stayed close to its set point of 37 °C.
- The skin temperature, at the surface, changed a lot.
Also accept
- constant internal environment; core near 37 °C, skin changes
Watch for
- “Homeostasis means the skin stays warm in the cold.” — The skin got much colder. Homeostasis keeps the core temperature steady.
2. WK2 · Final check
Model answer. In the cold the arterioles narrow (vasoconstriction): less blood flows through the surface capillaries, so less heat is lost. In the warm they widen (vasodilation): more blood flows near the surface, so more heat is lost.
A full answer includes
- Cold: the arterioles narrow (vasoconstriction); less blood near the surface; less heat lost.
- Warm: the arterioles widen (vasodilation); more blood near the surface; more heat lost.
Also accept
- cold narrow, less heat lost; warm widen, more heat lost
Watch for
- “In the cold the capillaries move deeper into the skin.” — Vessels do not move: the arterioles narrow.
3. FK1 · Final check
Model answer. Q is the hair erector muscle, T a hair, U a sweat gland and V a sensory neurone.
A full answer includes
- Q: hair erector muscle.
- T: hair.
- U: sweat gland.
- V: sensory neurone.
Also accept
- Q hair erector muscle; T hair; U sweat gland; V sensory neurone
Watch for
- “V is a blood vessel.” — V leads from the receptor near the surface: it is a sensory neurone.
4. FK2 · Final check
Model answer. The core temperature falls below its set point of 37 °C. Receptors in the skin and the brain detect the fall. The brain coordinates the response and sends impulses to the effectors: muscles shiver, releasing heat, and the arterioles supplying the skin surface capillaries narrow, so less heat is lost. The temperature rises back towards 37 °C: the response reverses the change.
A full answer includes
- The core temperature falls below the set point of 37 °C.
- Receptors in the skin and the brain detect the fall.
- The brain sends impulses to effectors: muscles shiver and arterioles supplying the skin surface narrow.
- Heat is released and less is lost, so the temperature rises back towards 37 °C: the change is reversed.
Also accept
- fall; receptors; brain; shivering and vasoconstriction; rises back
Watch for
- “The skin decides to make heat.” — The brain coordinates the response after receptors detect the fall.
5. GK1 · Final check
Model answer. (a) The pancreas secretes insulin into the blood, and insulin decreases the blood glucose concentration. (b) Insulin causes the liver and muscles to take up glucose; the liver converts it into glycogen and stores it, so the concentration falls back to normal.
A full answer includes
- (a) Insulin, secreted by the pancreas: insulin decreases the blood glucose concentration.
- (b) The liver (and muscles) take up glucose from the blood, and the liver converts it into glycogen and stores it.
Also accept
- (a) insulin, pancreas; (b) liver takes up glucose and stores it as glycogen
Watch for
- “Glucagon brings it down after a meal.” — Glucagon raises the blood glucose concentration. Insulin brings it down.
6. GK2 · Final check
Model answer. (a) When the blood glucose concentration falls, the pancreas secretes glucagon, which causes the liver to break down glycogen into glucose and release it into the blood. (b) Type 1 diabetes is treated by measuring the blood glucose concentration regularly and injecting insulin, with meals and exercise planned around it.
A full answer includes
- (a) The pancreas secretes glucagon; the liver breaks down glycogen and releases glucose into the blood.
- (b) Measuring the blood glucose concentration, injecting insulin, and planning meals and exercise.
Also accept
- (a) glucagon, liver releases glucose from glycogen; (b) measure, inject insulin, plan
Watch for
- “(a) The liver secretes glucagon.” — Glucagon is secreted by the pancreas. It acts on the liver.