Module 7 of 9Lesson 1 of 21 · B16 Homeostasis and temperature control by the skin
BGCSE Science Double Award · Biology · Form 5 · Section 14 Control of the internal environment
Lesson B16 · about 10 minutes

Homeostasis and temperature control by the skin

On a summer afternoon in Gaborone the air can reach about 35 °C. On a winter night in the Kgalagadi it can fall below 0 °C. Yet inside your body the temperature stays at about 37 °C, the best temperature for your enzymes. Your skin does the work — and your brain is in charge.

Prof KitsoIn 2024 Paper 3, Q10 most candidates lost marks here. They named the skin as the coordinating organ (it is the brain), dilated every vessel instead of the arteriole, and forgot the key words: more blood near the surface, more heat lost.
Gaborone,summer afternoon:about 35 °C Kgalagadi,winter night: canfall below 0 °C Inside you: about 37 °C
Papers 1 and 3Skin in 4 theory papers (2010–2022)Skin: 2024 Paper 3, Q10🔬 Skin thermoregulation lab

Learn5 cards

Homeostasis

is the maintenance of a constant internal environment.

Body temperature (about 37 °C), water and glucose are kept nearly constant. When one changes, detect it, the brain coordinates, and bring it back. The correction works against the change.

body temperaturerises or falls receptorsdetect it brain coordinates effectorscorrect it back to about 37 °C:a constant internal environment
The same loop works for a rise and for a fall.

The skin

The outer layer is the epidermis. Below it, in the dermis, are hairs, with ducts to pores, temperature receptors (nerve endings) and blood vessels: and capillaries.

A fat layer under the dermis insulates the body.

hairepidermishair erectormuscletemperaturereceptorfat layersweat porecapillaryarteriolesweat gland
How to label it: ruled lines that touch the part, no arrowheads, labels in columns.

Blood vessels near the surface

Too hot: arterioles near the surface dilate (). More blood flows near the surface, so more heat is lost by radiation.

Too cold: the arterioles constrict (). Less blood flows near the surface, so less heat is lost.

The vessels do not move — only their width changes.

too hot arteriole dilates:more blood flowsnear the surface→ more heat lostby radiationtoo cold arteriole constricts:less blood flowsnear the surface→ less heat lost
Why a face looks red after running: more blood near the surface.

Sweating, shivering and hairs

Too hot: sweat glands make more sweat. The water in it evaporates and takes heat from the skin.

Too cold: less sweat is made. — muscles contract quickly, and respiration in them releases heat. Tiny muscles raise the hairs, trapping a layer of air (only a small effect in humans).

too hottoo cold water vapour more sweat: waterevaporates, takingheat from the skin shivering: musclescontract quickly;respirationreleases heat hairs raised: trapair (small effect)
Sweat cools only when it evaporates.

The brain coordinates

Temperature receptors in the skin (and in the brain) detect the change. Nerve impulses go to the brain.

The brain the response: it sends impulses to the effectors — sweat glands, arterioles and muscles.

The skin carries out the response, but the brain is the coordinating organ.

temperature receptors in theskin (and brain) detect a change nerve impulses to the brain BRAIN coordinates sweatglandsarteriolesmuscles(shivering)
Exam answer for the coordinating organ: the brain.

See it live

Move the air-temperature slider from 5 °C to 45 °C and switch exercise on and off. Watch the sweat glands, the arterioles near the surface and shivering keep the core at about 37 °C — notice that the arterioles get wider, but never move.

Then label the skin, put the hot and cold flow charts in order, and describe the sweat-rate graph using both variables.

Skin thermoregulation labA section of skin that responds to heat, cold and exercise; label it, order the flow charts and describe a sweat-rate graph

Worked example3 examples

Example 1Grade C
Define homeostasis. Then name two effectors in the skin and say what each does on a hot day. [3]
definitionHomeostasis is the maintenance of a constant internal environment.
effector 1Sweat glands make more sweat; the water evaporates and takes heat from the skin.
effector 2Arterioles near the surface dilate, so more blood flows near the surface and more heat is lost by radiation.
Effector or receptor?Receptors detect the change; effectors respond. Sweat glands, arterioles and muscles are effectors. The temperature receptors only send impulses to the brain.
Example 2Grade B
The graph shows the sweat rate of a student at different air temperatures (example data). Describe the graph, then explain the change between 20 °C and 40 °C. [5]
0102030400200400600air temperature / °Csweat rate / cm³ per hour
Example data, not a real measurement.
describe 1From 10 °C to 20 °C the sweat rate stays low: it rises only from 40 to 50 cm³ per hour.
describe 2From 20 °C to 40 °C, as the air temperature increases, the sweat rate increases more and more steeply, from 50 to 600 cm³ per hour.
explain 1Temperature receptors in the skin detect the higher temperature and send impulses to the brain.
explain 2The brain coordinates: it sends impulses to the sweat glands, which make more sweat.
explain 3More water evaporates from the skin, so more heat is lost and the body temperature stays at about 37 °C.
Describe with both variablesName both quantities and every range: “from 20 °C to 40 °C, as the air temperature increases, the sweat rate increases”. “The graph goes up” or “the rate is constant” is not enough.
Example 3Grade A
Lorato leaves a warm classroom at 25 °C and waits outside on a Kgalagadi winter night at about 0 °C. Explain how her body keeps its temperature at about 37 °C. [6]
detectTemperature receptors in her skin detect the fall in temperature and send nerve impulses to the brain.
coordinateThe brain coordinates the response and sends impulses to the effectors.
arteriolesArterioles near the skin surface constrict, so less blood flows near the surface and less heat is lost by radiation.
sweatHer sweat glands make less sweat, so less heat is lost by evaporation.
shiveringHer muscles contract quickly (shivering); respiration in the muscles releases heat.
hairsHair erector muscles raise the hairs, trapping a layer of air that insulates — a small effect in humans.
Use comparative wordsEvery effect needs “more” or “less”: less blood near the surface, less heat lost. Never write that the blood vessels move away from the surface — they stay where they are and become narrower.

Misconception busterfrom the BEC examiner reports

The skin is the organ that coordinates temperature control.
The brain is the coordinating organ. The skin only carries out the response.

Examiner report: 2024 Paper 3, Q10(a)

Showing every blood vessel in the drawing as dilated.
Only the arteriole near the surface dilates.

Examiner report: 2024 Paper 3, Q10(b)(i)

Writing only that blood flows to the skin, or that heat is lost by conduction.
More blood flows near the skin surface, so more heat is lost by radiation.

Examiner report: 2024 Paper 3, Q10(b)(ii)

Describing the sweat-rate graph with one variable, or calling it constant.
Use both variables and every range: as the temperature of the surroundings increases, the rate of sweat production increases.

Examiner report: 2024 Paper 3, Q10(c)(i)

Mixing up vasodilation and vasoconstriction.
Dilation = wider (hot, more heat lost); constriction = narrower (cold, less heat lost).

Examiner report: 2024 Paper 1, Item 51

Blood vessels move closer to the surface when you are hot.
The vessels stay in place; the arterioles get wider, so more blood flows through the capillaries near the surface.

Common error (teacher experience)

Prof KitsoLearn the chain in order: receptor detects → brain coordinates → effector responds → more or less heat lost. Each link earns its own mark.

Quick check5 questions · Paper 1 style

1Which is the definition of homeostasis?

  1. ✓ Right. This is the syllabus definition, word for word.
  2. ✗ Not this one. That is excretion (lesson B17).
  3. ✗ Not this one. The body stays at about 37 °C whatever the air temperature.
  4. ✗ Not this one. That is respiration.

2Which organ coordinates the control of body temperature?

  1. ✗ Not this one. The skin carries out the response; it does not coordinate it.
  2. ✓ Right. The brain receives impulses from the receptors and sends impulses to the effectors.
  3. ✗ Not this one. A sweat gland is an effector.
  4. ✗ Not this one. The heart pumps blood; it does not control temperature.

3On a hot day, what happens to the arterioles near the skin surface?

  1. ✗ Not this one. Constriction happens in the cold, to keep heat in.
  2. ✗ Not this one. Blood vessels do not move.
  3. ✓ Right. Vasodilation: more blood near the surface, so more heat is lost by radiation.
  4. ✗ Not this one. Blood always reaches the skin; the amount changes.

4How does shivering help on a cold night?

  1. ✗ Not this one. That is the job of the hair erector muscles, not shivering.
  2. ✗ Not this one. True in the cold, but this is not shivering.
  3. ✗ Not this one. Evaporation cools the body — the opposite of what is needed.
  4. ✓ Right. Shivering muscles respire faster, and respiration releases heat.

5Which structures in the skin detect a change in temperature?

  1. ✗ Not this one. Sweat glands are effectors: they respond.
  2. ✓ Right. Receptors (nerve endings) detect the change and send impulses to the brain.
  3. ✗ Not this one. Arterioles are effectors: they dilate or constrict.
  4. ✗ Not this one. These muscles are effectors: they raise the hairs.

Exam cornerPaper 3 style · 10 marks

Fig. 10.1 shows a section through human skin.

ADCB
(a)
Name structures B and D. [2]
(b)
Name the organ that coordinates the control of body temperature. [1]
(c)
On a hot day, describe what happens to blood vessel C and explain how this helps to cool the body. [3]
(d)
Explain how structure B helps to cool the body on a hot day. [2]
(e)
Explain how shivering helps to keep the body warm on a cold night. [2]
Model answer

(a)

B: sweat gland.
D: temperature receptor.

(b)

The brain.

(c)

Arteriole C dilates.
More blood flows near the skin surface.
More heat is lost from the blood by radiation.

(d)

B makes more sweat.
The water in the sweat evaporates and takes heat from the skin.

(e)

Muscles contract quickly.
Respiration in the muscles releases heat, which warms the body.
Marking key — how the examiner awards the marks
Mark pointMark
(a)B: sweat glandB1
D: (temperature) receptor / nerve endingB1
(b)brain (accept hypothalamus / hypothalamus in the brain; reject skin)B1
(c)C (the arteriole) dilates / gets widerB1
more blood flows near the skin surface (reject “blood flows to the skin”)B1
more heat is lost by radiation (reject conduction)B1
(d)makes / secretes more sweatB1
the water (in sweat) evaporates, taking heat from the skinB1
(e)muscles contract quickly / repeatedlyB1
(more) respiration in the muscles releases heatB1

Total: 10 marks

Examiner tip. Copy the key words the examiners look for: arteriole, dilates, more blood near the surface, more heat lost by radiation, and brain for the coordinator. Anything you add in brackets must also be correct.

Rememberone-page card to download

  • Homeostasis = the maintenance of a constant internal environment (body temperature about 37 °C).
  • Receptors in the skin detect a change → impulses to the brain (coordinates) → effectors: sweat glands, arterioles, muscles.
  • Hot: arterioles dilate → more blood near the surface → more heat lost by radiation. Sweat evaporates and takes heat.
  • Cold: arterioles constrict; less sweat; shivering (respiration releases heat); hairs raised.
  • Blood vessels never move — only the arterioles change width.

Hot and cold compared

Too hotToo cold
sweat glands make more sweatsweat glands make less sweat
arterioles dilate: more blood flows near the surfacearterioles constrict: less blood flows near the surface
more heat lost by radiation and evaporationless heat lost
no shiveringshivering: respiration in muscles releases heat
hairs lie flathairs raised: trap a layer of air
Download this card (PDF)

Science that earnsa skill you can sell

Heat-safety kits for outdoor workers

Builders, farm workers and road crews work in the Botswana summer sun. They lose a lot of water as sweat. A heat-safety kit gives them a refillable water bottle, a wide-brim hat, a cotton neck cloth and your one-page leaflet.

Your leaflet uses this lesson: why sweating cools, why water lost as sweat must be replaced, and why shade and loose clothing help.

Example costs
10 refillable 1 litre bottlesP250
10 wide-brim hatsP350
10 cotton neck clothsP100
Leaflets printed (10)P30
Costs for 10 kitsP730
Sales: 10 kits at P100P1000
ProfitP270

Your leaflet is general safety information, not medical advice. It should say: rest in the shade and sip water often. Anyone who feels dizzy, sick or confused, has a bad headache or stops sweating in the heat needs medical help at once — call for help or go to the clinic. Sell only sealed, unopened items, and ask the site manager before you sell on a work site.

Example figures only — check prices in your local shops before you start.

Syllabus checklist Tap when you can do it

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Stadira Training Institute · Gaborone, Botswana · BGCSE Science Double Award (0569) Complete Tutor

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