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Skin Structure and Heat Regulation ICSE 9 Biology

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BiologyICSE Class 9 · Skin: Structure and Functions

Structure of the Skin, Glands and Heat Regulation (ICSE Class 9 Biology)

Updated 17 October 2026 · Fact-checked

The skin has an outer epidermis (a dead keratinised layer over a living germinative layer with melanin) and an inner dermis (with blood vessels, nerve endings, sweat glands, oil glands and hair follicles) over a fat layer. It protects, senses, excretes, makes vitamin D and keeps the body temperature steady by sweating, vasodilation and vasoconstriction.

Understand Structure of the Skin, Glands and Heat Regulation

1. Epidermis. The outer layer without blood vessels. The topmost *stratum corneum* is made of dead flattened cells filled with keratin and is waterproof and protective; below it the *germinative (Malpighian) layer* has dividing cells and *melanin* pigment cells that protect against ultraviolet light and give colour.

2. Dermis. A thick living layer of connective tissue containing blood vessels, lymph vessels, nerve endings (receptors for touch, pressure, pain, heat, cold), sweat glands, sebaceous glands, hair roots (follicles) and erector muscles. Under it is the *subcutaneous layer* with fat (insulation and energy store).

3. Glands. *Sweat glands* are coiled tubes that open by pores, releasing sweat (water, salts, a little urea) which cools the body. *Sebaceous glands* open into hair follicles and release oily *sebum* that keeps skin and hair soft and waterproof. Mammary glands are modified sweat glands that secrete milk after childbirth.

4. Hair and nails. Hair grows from follicles, traps air for insulation and protects; nails are made of keratin and protect finger tips.

5. Functions. Protection from germs, water loss and ultraviolet light; sensation; excretion of small amounts of wastes; production of vitamin D under sunlight; temperature regulation.

6. Heat regulation. In heat: blood vessels in the skin widen (*vasodilation*), more blood flows near the surface and heat is lost; sweat evaporates and cools. In cold: vessels narrow (*vasoconstriction*), less blood reaches the surface, heat is conserved; sweating stops and hair is raised by erector muscles, trapping air.

Structure of the Skin, Glands and Heat Regulation: key facts

Layers
  • Epidermis: dead keratin layer and germinative layer
  • Dermis
  • Subcutaneous fat
Glands
Sweatcooling and excretion
Sebaceoussebum
Mammarymilk
Pigment
Melanin protects from ultraviolet rays
Heat control
Hot: vasodilation and sweating | Cold: vasoconstriction, hair raised

Structure of the Skin, Glands and Heat Regulation in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Playing in summer

Suppose a student comes home from football on a hot afternoon with a flushed face and wet shirt.

Explain the skin response.

Try it first, then show the solutionSolution
  1. Heat produced in the muscles raises body temperature.
  2. Vasodilation brings warm blood to the skin so the face looks red.
  3. Sweat evaporates and cools the body.

Answer: Vasodilation and sweating lose heat.

Memory hook: Red and wet: cooling.

Tricks to remember Structure of the Skin, Glands and Heat Regulation

Short memory aids. Say each one aloud once, then use it on a question the same day.

  • D for Dilate = Discharge heat

    Vasodilation loses heat; vasoconstriction conserves it.

    Use it when: Heat regulation.

  • Sebum = oil

    Sebaceous glands: sebum oil.

    Use it when: Gland products.

Structure of the Skin, Glands and Heat Regulation: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Layers · 3 marks · Short answerBoard level

Name the layer of the skin that (a) contains melanin, (b) has blood vessels, (c) stores fat. [3]

Try it first, then show the solutionSolution
  1. (a) Germinative layer of epidermis.
  2. (b) Dermis.
  3. (c) Subcutaneous layer.

Answer: (a) Germinative layer (b) Dermis (c) Subcutaneous layer.

Example 2: Sweat vs sebum · 3 marks · Short answerHarder board level

Distinguish between sweat glands and sebaceous glands on structure, secretion and function. [3]

Try it first, then show the solutionSolution
  1. Sweat glands are coiled tubes opening at pores; sebaceous glands open into hair follicles.
  2. Sweat is watery with salts; sebum is oily.
  3. Sweat cools and excretes; sebum lubricates and waterproofs.

Answer: Sweat glands: watery sweat for cooling; sebaceous glands: oily sebum for lubrication.

Example 3: Cold day response · 4 marks · Long answerHarder board level

Describe the changes in the skin of a person who steps out into very cold weather, explaining each. [4]

Try it first, then show the solutionSolution
  1. Blood vessels narrow (vasoconstriction): less heat lost.
  2. Sweating stops: no evaporative cooling.
  3. Erector muscles raise hairs: trapped air insulates.
  4. Fat layer insulates the body.

Answer: Vasoconstriction, no sweating, raised hairs and fat insulation.

Example 4: Fever shivering · 3 marks · Short answerHarder board level

Why does the skin look pale and the body shiver at the start of a fever? [3]

Try it first, then show the solutionSolution
  1. The body temperature set point is raised.
  2. Skin blood vessels constrict, so the skin looks pale and less heat is lost.
  3. Muscles shiver to produce heat.

Answer: Vasoconstriction conserves heat while shivering produces heat.

Example 5: Case: sunburn · 6 marks · Case-basedHOTS / competency

Case. A fair-skinned child spends a day at the beach without cover and her skin turns red and painful. (i) Which pigment gives protection? [1] (ii) Which layer contains it? [1] (iii) Why does the skin of fair persons burn faster? [2] (iv) Suggest two protective measures. [2]

Try it first, then show the solutionSolution
  1. (i) Melanin.
  2. (ii) Germinative layer.
  3. (iii) They have less melanin to absorb ultraviolet rays.
  4. (iv) Wear covering clothes and use sunscreen or shade.

Answer: (i) Melanin (ii) Germinative layer (iii) Less melanin (iv) Covering clothes and sunscreen.

Where students lose marks in Structure of the Skin, Glands and Heat Regulation

The slips examiners see most often, and what to write instead.

  • Mistake: Saying the epidermis has blood vessels

    Layers are mixed.

    Do this: Blood vessels are in the dermis.

    Usually costs: 1 mark.

  • Mistake: Writing sweat contains only water

    Salts and urea omitted.

    Do this: Add salts and a little urea.

    Usually costs: 1 mark.

  • Mistake: Confusing vasodilation with vasoconstriction

    Direction reversed.

    Do this: Dilation widens, loses heat.

    Usually costs: 1 mark.

Exam tips

  • Draw a labelled section of skin.
  • Match each part with its function.
  • Explain heat regulation in both hot and cold conditions.
  • Mention keratin and melanin.

Practice questions on Structure of the Skin, Glands and Heat Regulation

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

  1. Q1 · 1 mark · MCQBoard level

    Sebum is secreted by:
    (a) sweat glands
    (b) sebaceous glands
    (c) mammary glands
    (d) salivary glands

    Hint

    Oil.

    Answer

    (b) sebaceous glands.

  2. Q2 · 2 marks · Very short answerBoard level

    What is keratin and where is it found in the skin? [2]

    Hint

    Protein.

    Answer

    A tough protein in the outer dead layer of the epidermis, hair and nails.

  3. Q3 · 2 marks · Very short answerBoard level

    Name two sensations received by the receptors in the dermis. [2]

    Hint

    Touch.

    Answer

    Touch, pressure, pain, heat or cold (any two).

  4. Q4 · 1 mark · Assertion-reasonHarder board level

    Assertion (A): Sweating helps to cool the body.
    Reason (R): Evaporation of sweat takes away heat from the body.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

    Hint

    Evaporation.

    Answer

    (a).

  5. Q5 · 3 marks · Short answerHarder board level

    Explain why the epidermis has no blood vessels yet remains alive in its lower layer. [3]

    Hint

    Diffusion.

    Answer

    The germinative layer gets nutrients by diffusion from the dermis below.

  6. Q6 · 3 marks · Short answerHarder board level

    Why does humid weather make us feel hotter even when the temperature is not high? [3]

    Hint

    Evaporation.

    Answer

    In humid air sweat evaporates slowly, so less heat is lost and we feel hotter.

  7. Q7 · 2 marks · Very short answerBoard level

    What happens to a mammal that cannot sweat, such as a dog, in hot weather? How does it cool itself? [2]

    Hint

    Panting.

    Answer

    It pants and loses heat through the tongue and mouth.

  8. Q8 · 3 marks · Short answerHarder board level

    Describe how the skin acts as an excretory organ and give a limitation. [3]

    Hint

    Little urea.

    Answer

    Sweat removes water, salts and a little urea, but the amount is small compared to the kidneys.

  9. Q9 · 4 marks · Case-basedHOTS / competency

    Case. A patient with burns over a large area risks dehydration and infection. (i) Which function of the skin is lost? [2] (ii) Why does he need extra warmth? [2]

    Hint

    Protection.

    Answer

    (i) Protection against water loss and germs. (ii) The insulating and heat-regulating role of the skin is damaged.

  10. Q10 · 4 marks · Case-basedHOTS / competency

    Case. In a cold room, a student notices goose pimples. (i) Name the muscles involved. [1] (ii) What do they do to the hair? [1] (iii) Why does this help the fur of an animal more than the hair of a human? [2]

    Hint

    Insulation.

    Answer

    (i) Erector muscles. (ii) Raise the hairs. (iii) Thick fur traps a good layer of air; human hair is sparse so the effect is small.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

  1. 1.Pigment of the skin?Show answer

    Melanin.

  2. 2.Oily secretion?Show answer

    Sebum.

  3. 3.Widening of blood vessels?Show answer

    Vasodilation.

  4. 4.Layer of dead cells?Show answer

    Stratum corneum.

  5. 5.Gland that gives milk?Show answer

    Mammary gland.

Structure of the Skin, Glands and Heat Regulation: frequently asked questions

Why do we get goose pimples?

Erector muscles raise hairs in cold.

Where is vitamin D made?

In the skin under sunlight.

Are nails living?

The visible nail is dead keratin.