Selina Concise Solutions for ICSE Class 9 Biology Chapter 13 Skin The Jack Of All Trades

Exercise 1

Question 1:
Answer: (d) the skin will turn dry and rough
Our skin needs natural oils produced by glands to stay soft and flexible. Without this moisture, the outer layer becomes brittle and can easily develop cracks.
Teacher's Tip: Think of your skin like a leather boot; it needs oil to stay soft and stop from cracking.
Exam Tip: Be sure to select the option that mentions both "dry" and "rough" to describe the texture change accurately.

Question 2:
Answer: (b) Albinism, Leucoderma
These conditions are related to the pigment called melanin which gives skin its color. Albinism is a total lack of pigment, while leucoderma causes white patches.
Teacher's Tip: "Albi" comes from the Latin word for white, just like the "Albino" animals you see in zoos.
Exam Tip: In your answer, clarify that albinism affects the entire body whereas leucoderma is localized to patches.

Question 3:
Answer: (c) Skin
The skin is actually the largest organ in the human body. It works hard every day to protect our internal systems from germs and weather.
Teacher's Tip: Don't forget that an organ is just a group of tissues working together for a big job, and skin does that perfectly!
Exam Tip: If asked for the "largest organ," the answer is always skin, not the liver or heart.

Question 4:
Answer: (b) Dermis
The dermis is the thick, inner layer of the skin located right beneath the epidermis. It contains important structures like blood vessels, nerves, and hair roots.
Teacher's Tip: Remember "D" for Dermis and "D" for Deep; it is the deeper layer of your skin.
Exam Tip: Note that while the epidermis is the outer shield, the dermis is where most of the skin's living functions happen.

Question 5:
Answer: (d) Palm
The skin on our palms and the soles of our feet is designed to be much thicker to handle constant friction. This thick skin also lacks hair follicles to provide a better grip.
Teacher's Tip: Look at your hands; the skin on your palm is much tougher than the skin on your arm because you use it to hold things.
Exam Tip: Identify the palm and sole as the primary areas of "thick skin" in the human body.

Question B.1:
Answer: Hypothalamus, a portion of the forebrain is the principal body heat regulating centre in our brain.
This tiny part of the brain acts just like a thermostat in a house. It senses when you are too hot or cold and triggers responses like sweating or shivering.
Teacher's Tip: Think of "Hypo-Therm" - "Therm" means heat, and this is your thermal controller.
Exam Tip: Always specify that the hypothalamus is located in the "forebrain" for a complete biological answer.

Question B.2:
Answer: Modified sweat gland: Mammary gland
Modified sebaceous gland: Ceruminous gland
Mammary glands are specialized to produce milk for nursing young ones. Ceruminous glands are found in the ear canal and produce protective earwax.
Teacher's Tip: "Cerumen" is the scientific name for ear wax, which makes "Ceruminous" easier to remember.
Exam Tip: Make sure you don't swap the two; mammary is a sweat gland modification while ceruminous is sebaceous.

Question B.3:
Answer: Sebaceous glands
These glands produce a natural oil called sebum that waterproofs our skin. It also helps to keep our hair from becoming dry and brittle.
Teacher's Tip: These are "Oil Spouts" located right next to your hair roots.
Exam Tip: Spelling is important! Practice writing "Sebaceous" to ensure you get full marks.

Question C.1:
Answer: 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.
Beyond cooling us down, the skin serves as a vital warehouse for nutrients. It also uses the sun's energy to create vitamins that keep our bones healthy and strong.
Teacher's Tip: Your skin is a "Storage Bin" and a "Vitamin Factory" all at once!
Exam Tip: Mention the "hypodermis" as the specific layer where fat is stored for extra marks.

Question C.2:
Answer: 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.
This reaction is a leftover from our ancestors who had much more body hair. By making the hair stand up, the body tried to trap a layer of warm air near the skin.
Teacher's Tip: Imagine your skin making tiny "tents" with your hair to catch warmth.
Exam Tip: Use the term "arrector muscles" to describe the mechanism that pulls the hair upright.

Question C.3:
Answer: 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.
Shivering is essentially your body's way of doing an emergency workout to create warmth. Rapid muscle movement generates thermal energy through the burning of stored fuel in your cells.
Teacher's Tip: Shivering is just "Exercise for Warmth" that your body does automatically.
Exam Tip: Include the term "metabolic rate" when explaining how shivering generates internal body heat.

Question C.4:
Answer: Leucoderma: Loss of skin pigmentation from smaller or larger patches at different regions of the body.
Albinism: Complete loss of pigmentation of the skin all over the body.
The main difference is the extent of pigment loss across the skin surface. Albinism is usually a genetic condition present from birth, while leucoderma can develop later.
Teacher's Tip: Think of "Patches" for Leucoderma and "Pure White" for Albinism.
Exam Tip: Use words like "complete" and "localized" to describe the difference in coverage between these two.

Question C.5:
Answer: 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.
These glands show how versatile our skin can be by adapting its structures for different needs. One keeps our ears clean while the other provides nutrition for newborn mammals.
Teacher's Tip: "Auditory canal" is just a fancy scientific way to say "Ear Hole."
Exam Tip: If asked for glands, always mention what they secrete (like ear wax or milk) for full credit.

Question C.6:
Answer: Fever and sickness or any kind of vigorous activity can lead to perspiration even in cold outside.
When you are sick, your body's internal thermostat resets to a higher temperature to fight off germs. Even if the air around you is chilly, your body will sweat to try and bring that fever down.
Teacher's Tip: Sweat is the "Body's Coolant," and it works whenever the internal engine gets too hot.
Exam Tip: Mention "fever" as the primary non-weather reason for sweating in your exam answers.

Question D.1:
Answer: Epidermis:
1. Stratum corneum: It is the outermost layer having layers of flattened dead cells made up of horny protein called keratin.
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.
Dermis:
It consists of elastic fibres, blood vessels, nerves, etc.
The epidermis acts as the waterproof shield of our body, constantly replacing its cells. The dermis is the thick foundation underneath that provides strength and sensation.
Teacher's Tip: Think of Epidermis as the "Shingles" on a roof and the Dermis as the "Wooden Beams" underneath.
Exam Tip: List the three layers of the epidermis in order (Corneum, Granular, Malpighian) for maximum marks.

Question D.2:
Answer: 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.
By changing the size of blood vessels, the body controls how much heat reaches the surface to be released. It's like opening or closing the windows in a room to regulate the temperature.
Teacher's Tip: "Dilation" means getting wider (like a wide door letting heat out). "Constriction" means squeezing shut.
Exam Tip: Be sure to explain how blood flow directly affects the amount of "sweat secretion" in different temperatures.

Question D.3:
Answer: (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.
The skin is our first line of defense against almost everything in the environment. It keeps out invisible bacteria, traps internal warmth, and acts as a shield against the sun's radiation.
Teacher's Tip: Think of your skin as a "Triple Guard" - Guarding against Germs, Cold, and Sun.
Exam Tip: When discussing UV rays, mention "melanin" if you want to show extra scientific depth.

Question E.2:
Answer: (a) 1. Sweat pore, 2. Sebaceous gland, 3. Sweat gland, 4. Fat, 5. Dermis, 6. Stratum malpighian, 7. Stratum corneum, 8. Epidermis, 9. 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.
This detailed anatomy shows how many different systems are packed into our skin. Each part, from the oily glands to the insulating fat, works together to keep our body stable and safe.
Teacher's Tip: Part 4 (Fat) is your body's "Pillow" and "Heater" combined into one layer.
Exam Tip: Practice drawing this diagram and labeling the nine parts to be ready for diagram-based questions.