Skin and negative feedback — answer key

1. FQ1 · Practice

Model answer. B is the hair erector muscle, joined to the side of the hair; it contracts to raise the hair. C is a sweat gland, a coiled tube deep in the skin with a duct to a pore on the surface.

A full answer includes

• B: hair erector muscle.
• C: sweat gland.

Also accept

• B hair erector muscle; C sweat gland

Watch for

• “C is a blood vessel, because it is a tube.” — C is coiled and has a duct to a pore on the surface: it is a sweat gland.

2. FQ2 · Practice

Options as numbered on the pupil sheet: 1 — insulates: slows the loss of heat; 2 — releases sweat onto the surface; 3 — carries impulses towards the brain; 4 — detects a change in temperature.

Model answer. The receptor detects a change in temperature. The sensory neurone carries impulses from it towards the brain. The fatty tissue insulates. The sweat gland releases sweat onto the surface.

A full answer includes

• receptor: detects a change in temperature; sensory neurone: carries impulses towards the brain; fatty tissue: insulates; sweat gland: releases sweat.

Also accept

• receptor detects; neurone carries impulses; fat insulates; gland sweats

Watch for

• “The sensory neurone releases sweat.” — A neurone carries impulses. Sweat comes from the sweat gland.

3. FQ3 · Practice

Options as numbered on the pupil sheet: 1 — The core temperature rises back towards the set point.; 2 — The brain sends impulses to the effectors.; 3 — Muscles shiver and the arterioles supplying the skin surface narrow.; 4 — The core temperature falls below the set point.; 5 — Receptors detect the fall..

Model answer. The change comes first, then the receptors detect it, the brain coordinates, the effectors respond, and the change is reversed.

A full answer includes

• The core temperature falls below the set point; receptors detect the fall; the brain sends impulses to effectors; muscles shiver and arterioles narrow; the core temperature rises back towards the set point.

Also accept

• fall; receptors; brain; effectors; rises back

Watch for

• “The brain acts before the receptors detect anything.” — The brain only responds to impulses from receptors that have detected a change.

4. FQ4 · Practice

Model answer. The feedback is negative because the response works against the change: a rise in temperature causes responses that lower it, and a fall causes responses that raise it, so the condition returns towards its set point.

A full answer includes

• The response reverses the change: a rise causes responses that lower the temperature, and a fall causes responses that raise it.

Also accept

• the response reverses the change

Watch for

• “Because the body does something harmful.” — "Negative" means the response works against the change, which is helpful.

5. FQ5 · Practice

Model answer. Temperature receptors are in the skin and in the brain itself.

A full answer includes

• In the skin and in the brain.

Also accept

• skin and brain

Watch for

• “Only in the sweat glands.” — Sweat glands are effectors. The receptors are in the skin and the brain.

6. FQ6 · Practice

Model answer. D is a receptor, a nerve ending near the surface. E is the sensory neurone leading from it. F is the blood vessels: an arteriole, the capillaries near the surface and a vein. G is the fatty tissue under the skin.

A full answer includes

• D: receptor.
• E: sensory neurone.
• F: blood vessels.
• G: fatty tissue.

Also accept

• D receptor; E sensory neurone; F blood vessels; G fatty tissue

Watch for

• “E is a blood vessel.” — E leads from the receptor and carries impulses: it is a sensory neurone.

7. FQ7 · Practice

Model answer. The drops are sweat, made by sweat glands. Each sweat gland is a coiled tube deep in the skin; a duct carries the sweat up to a pore on the surface.

A full answer includes

• Sweat glands.
• They are coiled tubes deep in the skin, joined to pores on the surface by ducts.

Also accept

• sweat glands, deep in the skin, ducts to pores

Watch for

• “The sweat glands are on the surface of the skin.” — Only the pores are on the surface. The glands are deep in the skin.

8. FQ8 · Practice

Model answer. The core temperature rises above its set point of 37 °C. Receptors in the skin and the brain detect the rise. The brain sends impulses to the effectors: sweat glands release sweat, and the arterioles supplying the skin surface capillaries widen. More heat is lost, so the core temperature falls back towards 37 °C, and the responses slow down.

A full answer includes

• The core temperature rises above the set point of 37 °C.
• Receptors in the skin and the brain detect the rise.
• The brain sends impulses to effectors: sweat glands release sweat and arterioles supplying the skin surface widen.
• More heat is lost, so the temperature falls back towards 37 °C.

Also accept

• rise; receptors; brain; sweating and vasodilation; falls back

Watch for

• “The sweat glands decide to sweat on their own.” — The brain coordinates: it sends impulses to the sweat glands after receptors detect the rise.

9. FQ9 · Practice

Model answer. (a) With sweating off in the warm room the core reached 37.4 °C: 0.4 °C above the set point. (b) With shivering off in the porch it fell to 36.6 °C: 0.4 °C below. With every response on it stayed within 0.1 °C.

Checked automatically

• (a) Above the set point with sweating off: 0.4 °C (within ±0.05 °C)
  • Common wrong answer 37.4 : That is the temperature itself. Subtract 37.0.
• (b) Below the set point with shivering off: 0.4 °C (within ±0.05 °C)
  • Common wrong answer 0.3 : That compares with 36.9 °C. Use the set point: 37.0 − 36.6.

A full answer includes

• (a) 37.4 − 37.0 = 0.4 °C.
• (b) 37.0 − 36.6 = 0.4 °C.

Also accept

• (a) 0.4 °C; (b) 0.4 °C

Watch for

• “(b) 0.3 °C.” — That compares 36.6 with 36.9 (all on). The question asks about the set point, 37.0 °C.

10. FQ10 · Practice

Model answer. Sweating is a response to the body being too warm: it loses heat. In the cold the body does not sweat anyway, so switching sweating off there changes nothing. To test sweating you must switch it off in the warm.

A full answer includes

• In the cold the body does not sweat, so switching sweating off changes nothing.
• Sweating only works when the body is too warm: it loses heat.

Also accept

• no sweating in the cold anyway

Watch for

• “Sweating does not help to control temperature.” — With sweating off in the warm room the core rose to 37.4 °C. Sweating helps, but only when the body is too warm.

11. FT1 · Apply

Model answer. (a) The set point is 25 °C. (b) The sensor detects the temperature, like a receptor. (c) The heater responds, like an effector. It is negative feedback because the response reverses the change: when the water cools below 25 °C the heater warms it back, and when it is above 25 °C the heater switches off.

A full answer includes

• (a) 25 °C.
• (b) The sensor.
• (c) The heater.
• The response reverses the change: a fall in temperature switches the heater on, raising the temperature back to 25 °C.

Also accept

• 25 °C; sensor; heater; response reverses the change

Watch for

• “The heater is the receptor.” — The heater responds; the sensor detects. Detecting is the receptor's job.

12. FT2 · Apply

Model answer. The hair erector muscles contracted and pulled the hairs upright, making the goose bumps. Receptors near the skin surface detected the cold and sent impulses along sensory neurones to the brain.

A full answer includes

• Hair erector muscles raised the hairs.
• Receptors in the skin detected the cold.

Also accept

• hair erector muscles; receptors

Watch for

• “The hairs raised themselves.” — Hairs have no muscle of their own: the hair erector muscle joined to each hair pulls it upright.

13. FT3 · Apply

Model answer. Shivering releases heat, so it matters in the cold. A fair test changes only the shivering switch, in the cold porch, for the same 10 minutes, and compares with the run with all responses on. The core fell to 36.6 °C instead of 36.9 °C.

A full answer includes

• Switch only shivering off and keep the person in the cold porch for 10 minutes; compare with all responses on in the porch.

Also accept

• shivering off in the porch, compared with all on

Watch for

• “Switch shivering off in the warm room.” — In the warm the body does not shiver, so nothing would change.