Skin

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

1. It protects the underlying tissues from mechanical shocks.
2. It holds the body fluids inside and prevents excessive loss of water by evaporation.
3. It prevents harmful substances or disease-causing germs from entering our body.
4. It protects the body against excess ultraviolet light which is potentially very harmful.

Respiration, storage of glycogen, digestion and secretion of hormone are not the functions of the human skin.

1. Stratum corneum (Cornified outermost layer)
2. Granular layer (middle layer)
3. Malpighian stratum (Malpighian layer or Germinative layer)

1. True
2. False
   Corrected statement— The cornified layer is hard and resistant to bacterial invasion.
3. True
4. True

Hairs provide the sensation of touch because nerve fibres extend up to their bases.

The oily secretion (sebum) of sebaceous gland makes the skin waterproof.

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

the skin will turn dry and rough

Reason — The sebaceous gland keeps the skin oily and conserves moisture in the body.
Body temperature regulation is mainly the function of sweat glands. Skin turning darker depends on melanin, produced by melanocytes.

Albinism, Leukoderma

Reason — In Leukoderma, skin pigmentation (melanin) is lost from smaller or larger patches at different regions of the body. In Albinism, complete loss of pigmentation occurs all over the body. Hair growth depends on hair follicles.

Skin

Reason — The skin prevents loss of heat in cold weather and facilitates loss of heat in hot weather.
The heart pumps blood. Lungs are involved in respiration (exchange of gases). The stomach is involved in digestion.

Dermis

Reason — Sweat glands are located in the dermis, which is the inner layer of the skin. Their ducts pass through the epidermis to open on the skin surface as pores. The epidermis is the outermost layer and does not contain glands, so sweat glands are not situated there.

Palm

Reason — Palm and sole have highly thickened epidermis.
The epidermis is very thin here to allow flexibility and movement. The epidermis is of normal thickness, not highly thickened. The epidermis is thin and delicate, which is why lips are sensitive.

Skin

Reason — Skin is the largest sense organ which forms the integument of our body.
Eyes belong to the visual system, not the integumentary system. The tongue is part of the digestive system and also acts as a taste organ. Ears belong to the auditory system (hearing and balance).

Adipose tissue

Reason — Adipose tissue is special type of tissue that stores fat.
This is the outer protective layer of skin, not involved in fat storage. Dermis does contain connective tissue, but fat storage specifically occurs in a specialized type of connective tissue, not all connective tissue. Muscular tissue is responsible for movement, not fat storage.

Hair shaft

Reason — Hair shaft is the part which projects from the skin and may extend slightly below the surface of the epidermis.
The hair bulb is the rounded base of the hair root, located inside the skin. It is not visible. The hair follicle is the tube-like structure in the skin that holds the hair root. It is also not visible externally. The hair papilla is a small structure at the base of the follicle that supplies nutrients to the growing hair. It is deep inside the skin.

Hypothalamus

Reason — Hypothalamus, present in the fore brain is the principal heat-regulating centre of our body.
The cerebrum controls thinking, memory, and voluntary actions, not temperature regulation. The thalamus mainly acts as a relay station for sensory information, not temperature control. The cerebellum is responsible for balance and coordination of movements, not heat regulation.

Prolactin

Reason — Prolactin is the hormone that is responsible for production of milk.
Progesterone mainly prepares the uterus for pregnancy and maintains it. It does not directly stimulate milk production. Oestrogen is responsible for development of female secondary sexual characteristics and growth of reproductive organs, but not milk secretion. Testosterone is a male sex hormone responsible for male secondary sexual characteristics.

P — Stratum corneum, Q — Germinative layer

Reason — Keratin is a fibrous structural protein that provides protection and waterproofing to the skin. It is found in the stratum corneum, the outermost layer of the epidermis, made up of dead, keratinized cells.
Melanin is the pigment responsible for skin color and UV protection. It is present in the germinative layer, the innermost layer of the epidermis.

P — Meibomian glands, Q — Ceruminous glands

Reason — Meibomian glands are modified sebaceous glands located along the margins of the eyelids. Their function is to secrete an oily substance that lubricates the eyelids.
Ceruminous glands are modified sweat glands found in the ear canal. They produce cerumen (earwax), which traps dust and germs, protecting the delicate eardrum.
Salivary glands are in mouth, help in digestion, not ear protection. Meibomian glands are eyelid glands and they do not protect eardrum.

(a) Skin proper and derivatives of skin.

(b) Epidermis and dermis.

(c) Three regions/sublayers of epidermis are :

1. Stratum corneum (Cornified outermost layer)
2. Granular layer (middle layer)
3. Malpighian stratum (Malpighian layer or Germinative layer)

(d) Five derivatives of skin are :

1. Hair
2. Nail
3. Mammary gland
4. Sweat gland
5. Sebaceous gland.

(e) Albinism, Leukoderma

(a) The contraction of erector 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.

(a) Melanin protects us from ultraviolet rays.

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

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

(d) Ceruminous glands are modified sweat glands.

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

(a) Skin — Skin is the outermost covering of the body stretching all over in the form of a layer. It is the largest organ of our body.

(b) Piloerection — In Piloerection, the hair is lifted due to contraction of the erector muscle and the surface of the skin presents a somewhat contracted and wrinkled appearance.

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

(d) Perspiration — The process of sweating out as a result of thermoregulation is called perspiration.

(e) Stratum malpighi — The innermost germinative layer of epidermis is called stratum malpighi.

(a) Difference between Leukoderma/Vitiligo and Albinism :

(b) Difference between Cold blooded and Warm blooded animals :

(c) Difference between Vasodilation and Vasoconstriction :

(d) Difference between Hibernation and Aestivation :

(e) Difference between Pimples and Black heads :

(a) Melanin — Malpighian layer (stratum malpighi) which is the innermost layer of the epidermis.

(b) Keratin — Nail.

(c) Hypothalamus — Fore brain.

(d) Granular layer — Middle layer of epidermis present below the outer cornified layer (stratum corneum).

(e) Matrix — Below the surface of the skin at the base of the nail.

(a) Cerumen — Wax like substance which protects and lubricates the delicate eardrum from dust particles and germs.

(b) Sebum — It makes the hair and outer surface of skin oily and waterproof.

(c) Keratin — In nails, Keratin forms the nail plate which provides a hard, protective covering over the nail bed.

(d) Melanin — It is responsible for colouration of the skin. It also protects the inner parts of the body from harmful ultraviolet rays of the Sun.

(e) Secretion of meibomian glands — It lubricates the margins of the eyelids and prevents the overflow of tears.

(a) Skin assists in the process of excretion of water, salts and to a very limited extent, urea through sweating. Since sweating occurs mainly for temperature regulation hence skin can be considered as an accessory excretory organ.

(b) A normal healthy young person can start perspiring even in cold atmosphere due to psychic influences such as fright or nervousness. This is referred to as "cold sweat".

(c) Hairs from different part of body show subtle differences. Hair follicles, found at the root of the hair, have the highest concentration of DNA, making them particularly valuable for DNA analysis. Therefore, hairs can be used in forensic investigation.

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.

"Goose-flesh" is the term used to describe the contracted and wrinkled appearance of the skin that occurs during winter or in response to certain emotions. It is caused by the contraction of the erector muscles, located between the hair follicles and the outer part of the dermis. These muscles pull the hair upright, causing the skin to appear rough and forming bumps on the surface.

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

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.

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.

It provides protection in the following ways:

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

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

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

Below diagram shows the generalized vertical section of mammalian skin:

(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.

(a) The process/condition shown in figures A and B are :

• A → Vasoconstriction
• B → Vasodilation

(b) Vasoconstriction occurs in cold climatic conditions. Vasodilation occurs in hot climatic conditions.

(c) The facial appearance of a person becomes pale or bluish during vasoconstriction and reddish during vasodilation.

(d) These situations may occur due to fright, nervousness or sudden emotion.

(a) Rohit has vitiligo whereas Rahman is suffering from albinism.

(b) Vitiligo is loss of pigment in patches of skin only whereas albinism is complete or near-complete absence of pigment in entire body (skin, hair, eyes)

(c) The pigment is located in the basal layer of the epidermis, in special cells called melanocytes.

(d) The name of the above pigment is melanin.

(e) More melanin means darker complexion and less melanin means lighter complexion.

Both A and R are true but R is not the correct explanation of A.

Reason — A is true because adipose cells store reserve food in the form of fat. These fat reserves provide energy during starvation.
R is true because adipose tissue is mainly found in the hypodermis or subcutaneous layer, beneath the dermis, not in the dermis itself.

Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.

Both A and R are true and R is the correct explanation of A.

Reason — A is true because keratin is a fibrous structural protein found in the stratum corneum, the outermost layer of the epidermis. R is true because keratin provides strength, waterproofing, and protection to the skin. It makes the skin tough, and reduces permeability, preventing excessive water loss and entry of pathogens.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

A is False and R is True.

Reason — A is False as leather is made from the dermis, not the epidermis. The dermis, being thick, tough, and durable, is what is treated to make leather.
R is True as the dermis contains dense irregular connective tissue, collagen, and elastic fibers, giving it strength and flexibility.

Therefore, A is False and R is True is the correct option.

Both A and R are true but R is not the correct explanation of A.

Reason — A is true because the skin is the largest sense organ of the human body. It contains sensory receptors for detecting pressure, pain, heat, and cold, playing a vital role in touch and temperature sensation.
R is true because the skin does help protect the body against mechanical, thermal, and physical injury and aids in perspiration but skin is not an organ of the nervous system.

Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.

Both A and R are true and R is the correct explanation of A.

Reason — A is true as vasoconstriction is the narrowing of blood vessels, not widening. It reduces blood flow to the skin, helping to conserve body heat during cold conditions or stress.
R is true because in cold weather, vasoconstriction helps reduce heat loss. It also occurs during nervousness or fear, redirecting blood flow to vital organs.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

(i) The glands that become more active during adolescence are the sebaceous glands.

(ii) The oily substance secreted by these glands is called sebum.

(iii) It lubricates and moisturizes the skin and hair, preventing them from becoming dry and brittle.

(iv) 1, 4 and 5

Reason — Pimples are not caused by inflammation of sweat glands. They are mainly due to sebaceous gland activity and blocked pores. Open pore gets clogged with dead skin cells and oxidation leads to blackheads. Pimples are not caused only by poor hygiene; hormones play a major role.

Body hairs are present in mammals to help regulate body temperature, protect the skin, and sense touch. They act as insulation in cold weather, protect against dust and injury, and help detect movements on the skin.

1. Feather
2. Both the structures help in maintaining a constant body temperature by trapping heat close to the body. This is essential for birds and mammals, as they are warm-blooded animals and need to keep their body temperature stable.