ICSE Solutions for Chapter 13 Skin: The Jack of all Trades Class 9 Biology Selina

Progress Check

1. List the four ways in which the skin serves as a protective layer for our body.

Solution

The four ways in which the skin serves as a protective layer for our body are:

  • It protects the underlying tissues from mechanical shocks
    • It holds the body fluids inside and prevents excessive water loss by evaporation
    • Checks the entrance of diseases or harmful substances causing diseases
    • Protects the body against excess ultraviolet light that can be harmful

 

2. Cross out the items in the following list which are not the functions of the human skin:

Sensation, respiration, storage of glycogen, excretion, digestion, temperature regulation, synthesis of vitamin D, secretion of hormone

Solution

The following are not the functions of the human skin:

  • Respiration
  • Digestion
  • Secretion of hormones


3. Name the three sub-layers of the epidermis from outer to inner.

Solution

The three sub-layers of the epidermis from outer to inner are as follows:

  • Outermost cornified layer
  • Middle granular layer
  • Inner malpighian layer


4. Write True(T) or false (F) for the following statements:

(i) Stratum corneum is made of dead cells having keratin
(ii) The malpighian layer is hard and resistant to bacterial invasion
(iii) The pigment melanin which imparts colouration to the skin is found in the Malpighian layer.
(iv) The dermis is very thick on palms and soles.

Solution

(i) True. The stratum corneum of the outermost layer made of several layers of flattened dead cells.

(ii) False. The cornified layer is a tough layer offering resistance to bacterial infection.

(iii) True,

(iv) True.

 

5. Match the items in Column I with those in Column II.

Column I

Column II

(i) Air spaces

a. Hair

(ii) Mammary glands

b. Sebaceous glands

(iii) “Goose-flesh”

c. Rudimentary in males

(iv) Traces of urea

d. Races of hot countries

(v) More numerous sweat pores

e. Gray hair

(vi) Oily secretion

f. Sweat

  Solution

Column I

Column II

(i) Air spaces

e. Gray hair

(ii) Mammary glands

c. Rudimentary in males

(iii) “Goose-flesh”

a. Hair

(iv) Traces of urea

f. Sweat

(v) More numerous sweat pores

d. Races of hot countries

(vi) Oily secretion

b. Sebaceous glands

 

6. How do hairs provide the sensation of touch?

Solution

Hair provide the sensation of touch as the nerve fibers extend up to their bases.

 

7. How is the outer surface of the skin made waterproof?

Solution

The outer surface of the skin is made waterproof due to the presence of sebaceous glands which secrete oil known as sebum to keep the epidermis supple and to prevent water loss by evaporation.

 

8. The statements given below have some parts printed in bold face. In case these parts are incorrect, rewrite these in correct form.

  1. All mammals are ectothermal.
  2. Hibernation is also known as summer sleep.
  3. Human body temperature normally is 98.6°F (37°C)
  4. Vigorous activity on a cold day overheats you.
  5. The principal heat-regulating centre is located in thyroid.
  6. Increased body heat causes vasoconstriction.
  7. Facial hair in humans contributes to sex differences.

Solution

  1. The statement is incorrect. All mammals are endothermal.
  2. The statement is incorrect. Hibernation is also known as winter sleep.
  3. The statement is correct.
  4. The statement is incorrect. Vigorous activity overheats on a hot day.
  5. The statement is incorrect. The principal heat-regulating centre is located in hypothalamus.
  6. The statement is incorrect. Increased body heat causes vasodilation.
  7. The statement is correct.

 

Review Questions

A. Multiple Choice Type

1. If for some reason the sebaceous glands fail to function:

(a) The body will not be able to regulate the body temperature
(b) The skin will turn darker with more melanin
(c) The hairs will fail to grow
(d) The skin will turn dry and rough

Solution

(d) The skin will turn dry and rough.
Sebaceous glands secrete oil to prevent water loss by evaporation and keep the epidermis supple.


2. Which one of the following pairs include the abnormal conditions of skin pigmentation?

(a) Leukoderma, Ringworm
(b) Albinism, Leukoderma
(c) Baldness, Albinism
(d) Rickets, Baldness

Solution

(b) Albinism, Leukoderma
Both are abnormal conditions of skin pigmentation.

 

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

(a) Heart
(b) Lungs
(c) Skin
(d) Stomach

Solution

(c) Skin
Skin prevents heat loss in cold and promotes heat loss in hot weather.

 

4. Sweat glands are situated in:

(a) Epidermis
(b) Dermis
(c) Both
(d) None of the above

Solution

(b) Dermis
Dermis is the inner thick layer of connective tissue and contains other structures such as hair follicles, sense organs, blood vessels etc.

 

5. The epidermis is highly thickened in:

(a) Eyelid
(b) Thigh
(c) Lip
(d) Palm

Solution

(d) Palm
Epidermis becomes thick and hard as on the palms, soles and even on heels.

 

B. Very short answer type

1. Name the principal body heat regulating centre in our brain.

Solution

Hypothalamus, a portion of the forebrain is the principal body heat regulating centre in our brain.

 

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

Solution

  • Modified sweat gland: Mammary gland
  • Modified sebaceous gland: Ceruminous gland

 

3. Name the skin glands which when inflamed cause acne.

Solution

Sebaceous glands Solution

 

C. Short Answer Type

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

Solution

Functions of the mammalian skin other than those concerned with heat regulation:

  1. Storage of food: Skin acts as a storehouse of energy by storing reserve food in the form of fat in the hypodermis.
  2. Synthesis of Vitamin D: Skin has the ability to synthesize small quantity of Vitamin D in the presence of sunlight.

 

2. What is “goose-flesh”? How is it brought about?

Solution

A peculiar roughness of the skin produced by cold or fear, in which the hair follicles become erect and form bumps on the skin is called goose flesh. Goose flesh occurs when the muscles at the base of hair known as erectors or arrectors, contract. The erector muscles are obliquely placed between the hair follicle and the outer part of dermis. They are smooth muscles that are necessary to move the hair. The contraction of erector muscle pulls the hair vertical and depresses the epidermis, resulting in goose flesh.

 

3. Why do you shiver and why do your teeth chatter when it is very cold in winter?

Solution

Man is a warm-blooded mammal. Our body must maintain an average temperature of 98.6 degree Fahrenheit to function properly. When we feel too hot or too cold, our nervous system sends certain automatic and autonomic reflexes that help to keep us warm. In cold weather, the blood vessels get narrowed (vasoconstricted). Shivering occurs when our muscles expand and contract rapidly to produce extra body heat. The amount of heat produced is increased by increased metabolic rate and muscular activity, which occurs in the form of shivering. That is why, our body shivers and teeth chatter to protect from cold by generating more heat.

 

4. What is the difference between leucoderma and albinism?

Solution

Leucoderma

Albinism

Loss of skin pigmentation from smaller or larger patches at different regions of the body .

Complete loss of pigmentation of the skin all over the body.

 

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

Solution

Two glands found in the human skin are:

  1. Ceruminous gland: It is a modified sebaceous gland found in the auditory canal. It secretes wax-like substance called ear wax.
  2. Mammary gland: It is a modified sweat gland. It is related to reproductive hormones and pregnancy.

 

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

Solution

Fever and sickness or any kind of vigorous activity can lead to perspiration even in cold outside.


D. Long Answer Type

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

Solution

Epidermis

Dermis

Stratum corneum: It is the outermost layer having layers of flattened dead cells made up of horny protein called keratin.

It consists of elastic fibres, blood vessels, nerves, etc.

Granular layer: It is very thin middle layer having two or three sublayers of flattened cells.

 

Malpighlan layer: It is the innermost region of the epidermis. The cells can actively divide to produce new cells.

 

 

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

Solution

Vasodilation: Dilation of blood vessels in the skin leading to an increase in the blood supply.

Vasoconstriction: Narrowing of blood vessels leading to reduction in the blood supply to the skin.

Temperature regulation in cold weather:

  1. At low temperature, the blood vessels get narrowed or vasoconstricted. This reduces the blood supply to the skin.
  2. There is less loss of heat by convection, conduction and radiation. There is less loss of heat through vapourization as reduced blood supply lowers the secretion of sweat by sweat glands.

Temperature regulation in hot weather:

  1. At high temperature, the blood supply to the skin is increased by vasodilation or dilation of blood vessels in the skin.
  2. This results in greater loss of heat by convection, conduction and radiation. There is more loss of heat through vapourization as more sweat is secreted due to rich supply of blood to the skin.

 

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.

Solution

(a) Entry of germs: Skin prevents the entry of harmful substances or infectious agents inside the body.

(b) Excessive loss of heat in severe cold: Skin prevents energy loss from the body. It conserves body heat in cold weather and facilitates loss of heat in hot weather.

(c) Entry of harmful ultra-violet rays: Skin protects the body against harmful ultraviolet light.

 

E. Structured/Application/Skill Type

1. Draw a labeled diagram of the generalized vertical section of the mammalian skin.

Solution


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

(a) Label the parts numbered from | to 9.

(b) State one main function of each of the following parts:
Part 2. _____  Part 3.____
Part 4. _____  Part 9. ____

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

(c) Part 4 may add to one’s good appearance or the “figure”. State one example of this function which may be common to both men and women.

Solution 

(a) 1. Sweat pore

  1. Sebaceous gland
  2. Sweat gland
  3. Fat
  4. Dermis
  5. Stratum malpighian
  6. Stratum corneum
  7. Epidermis
  8. Hair

 

(b) • Function of part 2 (Sebaceous gland): It produces oil called sebum, which plays a role in keeping our skin moist.

  • Function of part 4 (Fat): The skin reserves food in the form of a layer of fat.
  • Function of part 3 (Sweat gland): It secretes a transparent liquid (sweat) containing water and salts from the body in order to regulate body temperature.
  • Function of part 9 (Hair): Hair provide a sensation of touch and are also helpful In forensic investigations.

Part which has at least three functions:
Sebaceous gland:

  1. Skin protection
  2. Secretes an oily substance known as sebum that lubricates hair and skin of mammals.
  3. Presence of sebum enables to experience a wet skin even when we have not taken bath for days

(c) The one function which may be common to both men and women is that the fat serves as a food reserve and heat insulating layer as well as a shock absorber.



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