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Chapter 13

Skin - "The Jack of All Trades"

Class 9 - Concise Biology Selina


Multiple Choice Type

Question 1

If for some reason the sebaceous glands fail to function:

  1. the body will not be able to regulate the body temperature
  2. the skin will turn darker with more melanin
  3. the hairs will fail to grow
  4. the skin will turn dry and rough ✓

Question 2

Which one of the following pairs includes the abnormal conditions of skin pigmentation?

  1. Leukoderma, Ringworm
  2. Albinism, Leukoderma ✓
  3. Baldness, Albinism
  4. Rickets, Baldness

Question 3

Which one of the organs listed below, functions in regulating our body temperature most actively?

  1. Heart
  2. Lungs
  3. Skin ✓
  4. Stomach

Question 4

Sweat glands are situated in :

  1. Epidermis
  2. Dermis ✓
  3. Both
  4. None of these

Question 5

The epidermis is highly thickened in:

  1. Eyelid
  2. Thigh
  3. Lip
  4. Palm ✓

Very Short Answer Type

Question 1

Name the principal body heat regulating centre in our brain.

Answer

The principal body heat regulating centre in our brain is located in hypothalamus.

Question 2

Name any one modified sweat gland and any one modified sebaceous gland.

Answer

Modified sweat gland — Mammary gland

Modified sebaceous gland — Ceruminous gland

Question 3

Name the skin glands which when inflamed cause acne.

Answer

The skin glands which when inflamed cause acne are sebaceous glands due to hormonal imbalance.

Short Answer Type

Question 1

State any two functions of the mammalian skin other than those concerned with heat regulation.

Answer

The two functions of the mammalian skin are-

  1. The primary function of skin is to provide protection through four different means:
    1. Mechanical shocks.
    2. Prevention of excessive water loss.
    3. Prevents entry of diseases.
    4. Protects the body against excess ultraviolet light.
  2. The skin stores reserve food in the form of a layer of fat contained in special cells.

Question 2

What is "goose-flesh"? How is it brought about?

Answer

During winter or during some emotion our hairs get lifted and the surface of the skin presents a somewhat contracted and wrinkled appearance. This abnormal roughness of the skin generated by fear or cold wherein the hair follicles turn rigidly upright forming bumps on the skin is known as "goose-flesh".
These occur when the erectors contract. Erectors are the obliquely arranged muscles located between the base of the hair follicles and the outer part of the dermis. These smooth muscles are required to bring about motion of the hairs. When the erector muscles contract, it causes the hair to get pulled vertically thereby depressing the epidermis, causing "goose-flesh".

Question 3

What is the differences between leukoderma and albinism?

Answer

LeukodermaAlbinism
Skin pigmentation is lost from smaller or longer patches at different region of the body.Complete loss of pigmentation all over the body including hair, eyebrows, eyelashes and even the iris. Skin of such persons appears pinkish because of the underlying blood capillaries.

Question 4

Name any two glands found in the human skin. State their functions.

Answer

Two glands found in the human skin are:

  1. Sebaceous gland — They produce sebum, an oily secretion which makes the hair and the outer surface of the skin oily and waterproof to keep the epidermis supple and to prevent water loss by evaporation.
  2. Ceruminous gland — It secretes cerumen which lubricates and protects the delicate eardrum from dust particles and germs.

Question 5

An otherwise normal healthy young man started perspiring, while it was intensely cold outside, What could have been one reason for it ?

Answer

Perspiration can be caused even when it is intensely cold outside when the temperature of the body rises due to strenuous physical activity, fever and sickness (Hypertension, High blood pressure).

Long Answer Type

Question 1

Enumerate in a tabular form the different structures found in the epidermis and dermis of the human skin.

Answer

The different structures found in the epidermis and dermis of the human skin are:

EpidermisDermis
Stratum corneum (cornified layer) — It is the outermost layer of piled up dead cells of protein called keratin.It is the inner thick layer of connective tissue made of elastic fibers and is tough and flexible. it consists of nerve fibers, blood vessels, sense organs, hair follicles, sweat glands etc.
Granular layer — Thin middle layer having 2-3 sublayers of flattened cells. 
Malpighian layer (germinative layer) innermost layer of the epidermis where the cells divide actively to generate new cells. 

Question 2

Explain the terms “vasodilation” and “vasoconstriction”. How do these processes contribute in the regulation of the body temperature?

Answer

Vasodilation — It is the dilation of blood vessels in the skin that leads to an increase in the blood supply. Vasoconstriction — It is the narrowing of the blood vessels causing reduction in the blood supply to the skin.

Explain the terms “vasodilation” and “vasoconstriction”. How do these processes contribute in the regulation of the body temperature? Skin, Concise Biology ICSE Class 9.

Temperature Regulation:
In Cold Weather — When temperature is low, the blood vessels get narrowed. This reduces the blood supply to the skin. As a result, there is less loss of heat by convection, conduction and radiation and also less loss of it through vaporization of sweat because with reduced blood supply, the sweat gland secrete less sweat.
In Hot Weather — When outside temperature is high, there is vasodilation which results in greater loss of heat by radiation etc. and also by vaporization of sweat which is now produced in larger quantities due to the rich system of blood to the skin. Air movements over the body help to speed up evaporation of sweat leading to cooling effect on our body.

Question 3

How does our skin provide protection to our body against the following?

a) Entry of germs

b) Excessive loss of heat in severe cold

c) Entry of harmful ultra-violet rays.

Answer

It provides protection in the following ways:

(a) Entry of germs — The skin checks the entry of toxic substances or the agents causing infection into the body.

(b) Excessive loss of heat in severe cold — The skin prevents loss of heat in cold weather and facilitates loss of heat in hot weather.

(c) Entry of harmful ultra-violet rays — It protects the body against excess ultra violet light which is potentially very harmful.

Structured / Application / Skill Type

Question 1

Draw a labelled diagram of the generalized vertical section of mammalian skin.

Answer

Below diagram shows the generalized vertical section of mammalian skin:

Draw a labelled diagram of the generalized vertical section of mammalian skin. Skin, Concise Biology ICSE Class 9.

Question 2

Given below is a diagrammatic sketch of the vertical section of human skin.

Given below is a diagrammatic sketch of the vertical section of human skin. Label the parts numbered 1 to 9. State one main function of each of the following parts. Skin, Concise Biology ICSE Class 9.

(a) Label the parts numbered 1 to 9

(b) State one main function of each of the following parts:

  1. Part 2.
  2. Part 3.
  3. Part 4.
  4. Part 9.

(c) Name any one of the above parts which has at least three functions.

(d) Part 4 may add to one's good appearances or the "figure". State one example of this function which may be common to both men and women.

Answer

(a) The labels are as follows:

  • 1 → Sweat-pore
  • 2 → Sebaceous gland
  • 3 → Sweat gland
  • 4 → Fat
  • 5 → Dermis
  • 6 → Stratum Malpighian
  • 7 → Stratum corneum
  • 8 → Epidermis
  • 9 → Hair

(b)

  1. In the given figure, Part 2 is sebaceous gland. Its main function is to produce sebum to help keep the skin moist.
  2. In the given figure, Part 3 is sweat gland. It secretes a transparent liquid (sweat) containing water and salts from the body in order to regulate body temperature.
  3. In the given figure, Part 4 is Fat. The skin stores food in the form of a fat layer.
  4. In the given figure, Part 9 is hair. Hair provides a touch sensation. It can be also used in the forensic study.

(c) From the above parts, the one which has atleast three functions is Sebaceous gland. Its functions are the following:

  1. Protects skin
  2. Produces sebum that lubricates hair and skin of mammals.
  3. Sebum also protects from bacterial and fungal infections.

(d) In the given figure, Part 4 is fat. Fat accumulation in body plays a major role in determining if a person is overweight, underweight or just the right weight for both males and females. Person with balanced body weight is considered healthy. So, the right amount of fat at right places of body gives nice appearance and figure to both males and females.

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