ICSE Class 9 Biology Solutions Chapter 13 Skin -“The Jack of All Trades”

Class 9th ICSE Biology Solutions Chapter 13 Skin -“The Jack of All Trades”

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

1. Protects the underlying tissues from mechanical shocks.
2. Prevents excessive loss of water.
3. Prevents the entry of harmful substances or disease causing germs.
4. Protects the body against excess ultra-violet light.

Question 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.
Answer:
Respiration, Digestion, Secretion of hormone.

Progress Check

Question 1.
Name the three sub-layers of the epidermis from outer to inner:
Answer:

1. Comified layer
2. Granular layer
3. Malpighian layer

Question 2.
Write True (T) or False (F) for the following statements.
(i) Stratum corneum is made of dead cells having keratin. T/F
(ii) The Malpighian layer is hard and resistant to bacterial invasion. T/F
(iii) The pigment melanin which imparts colouration to the skin is found in the Malpighian layer. T/F
(iv) The dermis is very thick on palms and soles. T/F
Answer:
(i) T
(ii) F
(iii) T
(iv) T

Progress Check

Question 1.
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

Answer:
(i) e
(ii) c
(iii) a
(iv) f
(v) d
(vi) b

Question 2.
How do hair provide the sensation of touch?
Answer:
Hair provide a sensation of touch because nerve-fibres extend up to their bases.

Question 3.
How is the outer surface of skin made waterproof?
Answer:
Sebaceous glands sometimes open directly to the outside. They give out an oily secretion which makes the outer surface of the skin oily and waterproof.

Progress Check

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

Question 1.
All mammals are ectothermal.
Answer:
All mammals are endothermal.

Question 2.
Hibernation is also known as summer sleep.
Answer:
Hibernation is also known as winter sleep.

Question 3.
Human body temperature normally is 98.4C.
Answer:
Human body temperature normally is 37°C.

Question 4.
Vigorous activity on a cold day overheats you
Answer:
Vigorous activity on a cold day warms you.

Question 5.
The principal heat-regulating centre is located in the thyroid.
Answer:
The principal heat-regulating centre is located in the hypothalamus.

Question 6.
Increased body heat causes vasoconstriction.
Answer:
Increased body heat causes vasodilation.

Question 7.
Facial hair in human contributes to sex differences.
Answer:
Facial hair in human males contributes to sex differences.

Review Questions

A. Multiple Choice Type :

Question 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
Answer:
(d) the skin will turn dry and rough

Question 2.
Which one of the following pairs includes the abnormal conditions of skin pigmentation?
(a) Leucoderma, Ringworm
(b) Albinism, Leucoderma
(c) Baldness, Albinism
(d) Rickets, Baldness
Answer:
(b) Albinism, Leucoderma

Question 3.
Which one of the organs listed below, functions in regulating our body temperature most actively?
(a) Heart
(b) Lungs
(c) Skin
(d) Stomach
Answer:
(c) Skin

Question 4.
Sweat glands are situated in:
(a) Epidermis
(b) Dermis
(c) Both
(d) None of the above
Answer:
(b) Dermis

Question 5.
The epidermis is highly thickened in:
(a) Eyelid
(b) Thigh
(c) Lip
(d) Palm
Answer:
(d) Palm

B. Very Short Answer Type:

Question 1.
Name the principal body heat regulating centre in our brain.
Answer:
Principal body heat regulating centre in our brain is located in the hypothalamus a portion of the fore brain. It acts as a thermostat. When the body tends to cool below the normal temperature. It switches on or speeds up the heat producing process, and when the body tends the become overheated, it increases the cooling process and heat producing process is switched off.

Question 2.
Name any one modified sweat gland and any one modified sebaceous gland.
Answer:
Modified sweat gland is mammary gland modified sebaceous gland is ceruminous gland.

Question 3.
Name the skin glands which when inflamed cause acne.
Answer:
Sebaceous glands.

C. Short Answer Type

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

1. Synthesis of vitamin D
2. Protection against mechanical shocks.

Question 2.
What is “goose-flesh”? How is it brought about?
Answer:
During winter or some emotion our hair get lifted and the surface of the skin presents a somewhat contracted and wrinkled appearance, This experience is known as “goose- flesh” “Goose-flesh” is caused’by the erector muscle of hair which runs obliquely between the hair follicle and the outer part of the dermis. Due to contraction of this muscle at one end pulls the hair to vertical position, and at the other end, depresses the epidermis.

Question 3.
Why do you shiver and why do your teeth chatter when it is very cold in winter?
Answer:
In cold weather the blood vessels get narrowed (vasoconstriction). This reduces the blood supply and as a result, there is less loss of heat and person shivers and his teeth chatter.

Question 4.
What is the difference between leucoderma and albinism?
Answer:

Leucoderma	Albinism
Skin pigmentation is lost from smaller or longer patches at different regions 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 5.
Name any two glands found in the human skin. State their functions.
Answer:
1. Sweat Glands-Secretory part of sweat gland absorbs fluid from the surrounding cells and blood capillaries of dermis and passes it into the excretory sweat duct which pours it out on the surface. Sweat consists of 99% water,0.2-0.5% salts, p.08% urea.

2. Mammary glands-These are related to the reproductive hormones and pregnancy-the-milk secreted by the mammary glands is highly nutritious for newly born baby. ’

Question 6.
An otherwise normal healthy young man started – perspiring, while it was intensely cold outside, What could have been one reason for it?
Answer:
Fever and sickness (Hypertension, High blood Pressure)

D. Long Answer Type

Question 1.
Enumerate in a tabular form the\different structures found in the epidermis and dermis’ of human skin respectively.
Answer:
The principal components of the human skin are as below:

Question 2.
Explain the terms “vasodilation” and “vasoconstriction”. How do these processes contribute in temperature- regulation of the body?
Answer:
Vasodilation-Dilation of blood vessels in the skin leading to increase in blood supply.

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

Temperature-regulation
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, vaporisation of sweat because With reduced blood supply, the sweat glands secrete less sweat.

Hot Weather-When outside temperature is high, there is vasodilation which results in greater loss of heat by radiation etc. and also by vaporisation 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:
(a) Entry of germs-Prevents the entry of harmful substances or disease causing germs.

(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 via vasoconstriction and vasodilation.

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

E. Structured / Application / Skill Type

Question 1.
Draw a labelled diagram of the generalised vertical section of mammalian skin.
Answer:

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

(a) Label the parts numbered from 1 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.
Answer:
(a)

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

(b)
2. Sebaceous gland-Secretion of oil which makes the hair and outer surface of skin oily and waterproof.

3. Sweat Gland-Secretory part of sweat gland absorbs fluid from the surrounding cells and blood capillaries of dermis and passes it into the excretory sweat duct which pours it out on the surface. Sweat consists of 99% water, 0.2-0.5% salts; 0.08% urea.

4. Fat-Food reserve and also as a heat-insulating layer.

9. Hair-Provide a sensation of touch because nerve of fibres extend up to their bases.
Sebaceous glands have three functions.
(c) Fat cells (adipose tissue)-This subcutaneous fat serves as a food reserve and also as a heat-insulating layer.

Can You Guess :

Why are body hair present in mammals?

Hair and feathers :
1. Hair and feathers in the mammals and birds are exoskeleton. Hair and feather are protective in nature. The large coat of hair in the polar animals does not allow the heat of the body to go out. Those hairs insulate the body against the intense cold and save the body from the bitter cold. In the polar regions as polar bears, tigers have thick coating of hair to save them from severe cold.

2. Hairs give sensation of touch as nerve fibres extend up to their bases.

3. Eye lashes prevent the entry of foreign particles in the eyes.

4. Similarly hairs in the nose prevent the entry of dust. Similarly feathers are exoskeletons and help the birds in flying. Birds have feathers for flying and covering the body to save them from cold and other unfavourable weather conditions.

LOOK AT THE FOLLOWING DIAGRAM

A counterpart of mammalian hair, in birds ………………

This structure in birds is a counterpart of mammalian hair.

Question 1.
What is this?
Answer:
(A feather of a bird) (But this one is secondarily adapted for flight).

Question 2.
What is the one common primary function served by these structures both in birds and mammals?
Answer:
Provides warmth to body by acting as an insulating layer – of air. Both feathers and hair.

Question 3.
What are the other categories of this structure in birds?
Answer:
(a) Flight feathers
(b) Down feathers
(c) Filoplumes

Extra Questions

Question 1.
Out of the organs listed below select the one that most actively functions in regulating our body temperature.
(a) Heart
(b) Lungs
(c) Skin
(d) Stomach
Answer:
Skin actively participates in regulating our body temperature.

Question 2.
In the diagram given below label the following parts. Sweat pore, sweat duct, hair follicle, erector muscle, sweat gland, sebaceous gland, subcutaneous fat.

Answer:
seven parts are shown in diagram

Question 3.
Why should be keep our skin clean?
Answer:
Skin must be kept clean otherwise pores get blocked with dust, grease and germs attack and breed over there causing various diseases.
A clean intact skin is a barrier to bacteria and fungi. So regular bathing with a mild soap and using clean dry towel will keep the hair follicles open.

Question 4.
What basic care must be taken to maintain our skin healthy?
Answer:
Skin: Skin must be kept clean otherwise pores get blocked with dust, grease and germs attack and breed over there producing foul smell.

A clean intact skin is a barrier, to bacteria and fungi. So regular bathing will keep the hair follicles open. Soap dries out the skin and strips it off its protective sebum. Strong. soaps can even cause allergic reactions like itching and soreness. Hence a mild soap is recommended.

Question 5.
Why is it advisable to use a mild soap?
Answer:
Mild soap is recommended for skin as strong soaps can cause allergic reactions like Itching and soreness. Soap dries out skin and strips it off its protective sebum.

Question 6.
Name the three derivatives of the skin.
Answer:

1. Hair
2. Nails
3. glands and several specialised receptors.

Question 7.
In which region of the skin (epidermis or dermis) are the following located? Also state the function of each :
(i) Malpighian layer :
(ii) Sweat gland :
(iii) Sebaceous gland :
(iv) Cornified layer :
(v) Granular layer :
Answer:
(i) Epidermis- It prevents the loss of Tissue fluid. It gives colour to skin and protects body against harmful effect of ultra-violet rays.

(ii) Dermis – Regulate the body temperature and eliminates about 1% of metabolic waste through sweat.

(iii) Dermis- Keep skin soft and supple and prevents it from drying up.

(iv) Epidermis-Protects underling tissues from mechanical damage, bacterial invasion and dehydration.

(v) Epidermis- Its function is to form KERATIN- a protein found in hair and nails.

Question 8.
Why is it advisable to wear gloves when working in the garden dr when washing clothes and dishes?
Answer:
There is always threat, hand have to face [While working in the garden or when washing clothes and dishes] of infection from the soil or is subjected to chemical irritants like detergents. Hands can be protected by wearing gloves They also protect fingernails from picking germs.

ICSE Class 9 Biology Solutions