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Class 9 SELINA Solutions Biology Chapter 13 - Skin - The Jack Of All Trades

Skin - The Jack Of All Trades Exercise Ex. 1

Solution A.1(a)

(iv) the skin will turn dry and rough

Solution A.1(b)

(ii) Albinism, Leukoderma

Solution A.1(c)

(iii) Skin

Solution A.1(d)

(ii) Dermis 

Solution A.1(e)

(iv) Palm 

Solution A.1(f)

(iv) Skin 

Solution A.1(g)

(iii) Adipose tissue

Solution A.1(h)

(iv) Hair shaft

Solution A.1(i)

(i) Hypothalamus

Solution A.1(j)

(ii) Prolactin

Solution B.1

(a) Skin proper and Derivatives of the skin

(b) Epidermis and Dermis

(c) Cornified layer, Granular layer and Malpighian layer

(d) Hair, Nails, Sebaceous glands, Sweat glands and Mammary glands

(e) Leukoderma (Vitiligo) and Albinism

Solution B.2

(a) The contraction of erector (arrector) muscle pulls the hair to a somewhat vertical position.

(b) The oily secretion sebum makes the skin waterproof.

(c) Cornified layer of the skin is composed of flattened dead cells.

(d) The hard outer part of the nail is termed as plate.

(e) Meibomian glands open on the margins of the eyelids.

Solution B.3

(a) Melanin protects us from ultraviolet rays.

(b) Vitamin D can be synthesized when skin is exposed to sunlight.

(c) Acne is caused due to hormonal influence and inflammation of the sebaceous gland.

(d) Mammary glands are modified sweat glands.

(e) The optimum temperature for enzymatic activity in our body is 35°C to 40°C. 

Solution C.1

(a) Skin is the body's largest organ, made of water, protein, fats and minerals accounting for 15% of an adult human's total body weight.

(b) Piloerection is the reflex process in which the erector hair muscles contract and cause the hair to stand erect.

(c) Heatstroke or sunstroke is a condition in which sweat production is unable to keep pace with its evaporation in very hot winds.

(d) Perspiration, also known as sweating is the process by which sweat poured in the sweat glands is eliminated from the skin surface to lose body heat by evaporation.

(e) Stratum malpighi also called as germinative layer, is the innermost region of the epidermis which contains actively dividing cells.

Solution C.2

(a) Differences between Leukoderma/Vitiligo and Albinism:


 (b) Differences between Cold blooded and warm-blooded animals:


 (c) Differences between Vasodilation and Vasoconstriction:


(d) Differences between Hibernation and Aestivation:


(e) Differences between Pimples and Black heads:


Solution C.3

(a) Melanin: Contained in the cells of the malpighian layer of the skin epidermis.

(b) Keratin: Found in nails, hairs, horns and hooves.

(c) Hypothalamus: Found in forebrain hidden between the cerebral hemispheres.

(d) Granular layer: Located in the middle of the epidermis consisting of two or three sub-layers of flattened cells.

(e) Matrix: Located just below the skin surface at the base of the nail.

Solution C.4

(a) Cerumen lubricates and protects the delicate eardrum from dust particles and germs.

(b) Sebum makes the hair and the outer surface of the skin oily and waterproof to keep the epidermis supple and prevent the loss moisture by evaporation.

(c) Keratin is the fibrous structural protein found in the hair, nails, horns, hooves and epidermis of the skin.

(d) Melanin is the skin pigment which gives colouration to the skin.

(e) Secretion of meibomian glands is oily and serves to lubricate the margins of the eyelids and prevent the overflow of tears.

Solution C.5

(a) The skin, lungs, and liver of vertebrates are accessory excretory organs. The skin assists in the process of excretion of water, salts and urea in the form of sweating. Since sweating from the skin occurs mainly for temperature regulation, skin cannot be considered as the main excretory organ. It is said to be an accessory excretory organ.


(b) Cold sweat may occur due to psychic influences such as fright and nervousness. A person can sweat when he is anxious or suffering from hypertension or cardiac arrest. In such cases, the adrenaline hormone causes the blood pressure to rise. The skin begins to perspire to expel the increasing body temperature. Sweating may also accompany nausea and severe pain.


(c) Hairs from different parts of the body such as chest, arm pit, beard and nose show subtle differences. As hair can be transferred during physical contact, the presence of hair can associate a suspect with a victim or a suspect/victim to a crime scene. The type of hair recovered, and the condition and number of hairs found all impact on their value as evidence in a criminal investigation.

Solution C.6

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

(i) Storage of food: Skin acts as a storehouse of energy by storing reserve food in the form of fat in the hypodermis.

(ii) Synthesis of Vitamin D: Skin has the ability to synthesize small quantity of Vitamin D in the presence of sunlight.

Solution C.7

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.

Solution D.1



1. 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.

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

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


Solution D.2

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.

Solution D.3

(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.

Solution E.1


            Vertical section of the mammalian skin

Solution E.2


1: Sweat pore

2: Sebaceous gland

3: Sweat gland

4: Fat

5: Dermis

6: Stratum malpighian

7: Stratum corneum

8: Epidermis

9: Hair


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.

(c) Part which has at least three functions (Sebaceous gland):

(i) Skin protection

(ii) Secretes an oily substance known as sebum that lubricates hair and skin of mammals

(iii) Presence of sebum enables to experience a wet skin even when we have not taken bath for days

(d) 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. 

Solution E.3

(a) Vasoconstriction (A) and Vasodilation (B).

(b) Vasoconstriction occurs in cold weather whereas vasodilation occurs in hot weather.

(c) When vasoconstriction occurs, it makes a person look pale or bluish because of the reduced blood supply to the skin. In vasodilation, the person's face turns reddish due to the rich supply of blood to the skin.

(d) Some emotional problems, such as stress or danger tighten the blood vessels (vasoconstriction) and strong emotions can lead to shortness of breath and rapid breathing (vasodilation).

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