NCERT Solutions for Class 7 Science Chapter 9 Life Processes in Animals (PDF) – 2027

Complex food components (carbohydrate, protein and fat) are broken down into simpler forms in a long tube called the alimentary canal, which runs from the mouth to the anus. Digestive juices from its different parts break the food down; the simple forms are absorbed into the blood, which carries them to all parts of the body.

No, it is not the same in all animals. Cows and buffaloes bring swallowed food back to the mouth to chew it again (rumination); birds have no teeth and grind food in a gizzard.

Yes. Just thinking about a favourite food — hot samosas, a bowl of rasgulla, mango pickle — makes the mouth feel watery. This happens because more saliva is released in the mouth when you recall your favourite food.

Animals eat different kinds of food, in different ways.

Saliva moistens the food, making it soft and easy to swallow, and it contains a digestive juice that breaks down starch into sugar.

When we chew a chapati for a long time (30–60 seconds), it begins to taste sweet, because saliva changes the starch in it into sugar.

Yes — the taste changes. The chapati or rice slowly begins to taste sweet as you keep chewing.

Our elders cleaned their teeth with a datun (a neem or babool twig chewed into a brush) or with a tooth powder (manjan) of charcoal or salt. They scraped the tongue with a metal jibhi, rinsed the mouth (kulla) after every meal, and chewed saunf or clove after food.

Iodine is the test for starch: it turns blue-black where starch is present, and stays its own brownish-orange colour where starch is absent.

The starch in the boiled rice causes it. Iodine gives a blue-black colour with starch. The rice in test tube A was not chewed, so no saliva acted on it and its starch was still present.

Changes to make: chew the rice for longer (say 90–120 seconds), chew it more thoroughly, take a smaller amount of rice, or let the tube stand for a few minutes before adding iodine — changing only one thing at a time.

Yes. The longer we chew, the more starch is changed into sugar, so the blue-black colour becomes lighter and may not appear at all.

The food does not fall down by its own weight — it is pushed. The walls of the food pipe gently contract and relax in a wave-like motion, and this travelling wave squeezes the food forward into the stomach.

The alimentary canal is very long. The small intestine alone is almost 6 metres long — about twice the height of a classroom — and the large intestine is about 1.5 metres long. So the whole canal is more than 7.5 metres long.

The inner lining of the small intestine is thin and has thousands of finger-like projections that increase its surface area. Digested nutrients pass through this thin lining into the blood in the blood vessels of its wall, and the blood carries them to all parts of the body. This is called absorption.

It moves on into the large intestine. There:

1. The large intestine absorbs water and some salts from it, so the watery waste becomes semi-solid.
2. This semi-solid waste is called stool.
3. The stool is stored in the rectum, the lower part of the large intestine, until the body is ready to get rid of it.
4. Finally it is expelled through the anus — a process known as egestion.

Because it is named for its width, not its length. The large intestine is only about 1.5 m long against the small intestine’s 6 m, but it is much wider than the small intestine — and that is why it is called “large”.

The cow is ruminating. Cows partially chew grass and swallow it into the stomach, where it is partially digested. Later, this partially digested food is brought back to the mouth and chewed slowly and thoroughly. This process is called rumination, and such animals are called ruminants. The chewed food then passes down the alimentary canal again for further digestion.

The oxygen is used to break down glucose (sugar from digested food) and release energy. This process is called respiration.

Yes, breathing and respiration are different. Breathing is taking air in and giving it out — a physical process. Respiration is the breakdown of glucose using oxygen inside the body to release energy — a chemical process.

The body stores food and holds water, so we can manage for some days without food and for a day or two without water. But oxygen cannot be stored in the body; it is needed every moment to break down glucose and release energy. When breathing stops, the oxygen supply stops, energy is no longer released, and organs such as the brain begin to fail within minutes.

Yes. There are tiny hair inside the nostrils. These hair, along with mucus, trap dust and dirt from the air we breathe in, so that clean air goes down to the lungs.

That is why we should breathe through the nose and not through the mouth.

Air enters through the nostrils and passes through the nasal passages and the windpipe into the lungs, where it fills tiny sacs called alveoli.

Breathing in: the ribs move up and outwards and the diaphragm moves down, so the space in the chest increases and air enters the lungs. Breathing out: the ribs move down and inwards and the diaphragm moves up, so air is pushed out.

When you pull the rubber sheet downwards, the balloons inflate (blow up). When you release the rubber sheet upwards, the balloons deflate (go flat again).

In this model, the balloons represent the lungs and the rubber sheet represents the diaphragm.

Yes. The lime water in test tube B, into which exhaled air was blown through a straw, turns milky. The lime water in test tube A, into which the air we inhale was passed with a pichkari, does not change.

It indicates that the air we breathe out contains more carbon dioxide than the air we breathe in.

Food gives us energy only with the help of the oxygen we breathe. Digested food is broken down into simple substances like glucose, which the blood carries to all parts of the body. Oxygen from the inhaled air also reaches them through the blood. There, oxygen helps break down glucose to release energy — this is respiration.

Birds breathe through lungs, like humans. Fish breathe through gills, which are richly supplied with blood vessels; oxygen dissolved in the water passes into the blood across the gills, and carbon dioxide passes out. Different animals have different breathing organs to suit their habitats.

The three empty boxes are the food pipe (oesophagus), the small intestine and the large intestine.

Iodine turns blue-black wherever starch is present, and keeps its own brownish-orange colour where starch is absent.

The correct answer is (iii) To help in inhalation and exhalation.

The diaphragm is a dome-shaped muscle below the lungs. It moves down during inhalation (space in the chest increases and air enters the lungs) and up during exhalation (space decreases and air is pushed out).

(i)–(a), (ii)–(d), (iii)–(e), (iv)–(b), (v)–(c)

Sanvi can ask Anil:

1. “Where does the energy in our body come from? Does just taking air in and out release energy?”
2. “Breathing takes place in the nose, windpipe and lungs. In which part of the body does respiration take place?”
3. “Breathing is a physical process. Is breaking down glucose with oxygen (respiration) also a physical process?”
4. “When you hold your breath for a few seconds, does respiration in your body also stop?”

Tanu’s statement is correct. We inhale air, which is a mixture of gases, not pure oxygen; this air has nearly 21% oxygen, much more than the air we breathe out (16–17%). Anu’s statement is true but incomplete, and Shanu’s is wrong because we never inhale only oxygen.

Possible explanations:

• The tiny hair and mucus in the nose can trap only a limited amount of dust; when the air is very dusty, many particles get through.
• The dust particles irritate the lining of the nasal passages.
• Sneezing is the body’s protective reaction: a sudden, strong rush of air through the nose and mouth throws the dust out, so that it does not reach the lungs.

Any two of these:

1. Anusha may have run faster or farther, so her muscles needed more energy. Releasing more energy needs more oxygen, so she had to breathe faster.
2. Anusha may be less used to running than Paridhi; a person who exercises regularly needs fewer breaths for the same work.
3. She may have counted her breaths sooner after stopping, or she may have a cold or a blocked nose.

Yadu wants to test whether saliva breaks down (digests) starch.

Tube A (rice flour + water) turns blue-black, so starch is still present in it. Tube B (rice flour + water + saliva) does not turn blue-black, so its starch has been broken down. Saliva is the only difference between the two tubes, so the change is due to saliva.

Rakshita is trying to find out whether the air we breathe out contains more carbon dioxide than the air we breathe in.

To confirm: if the lime water in tube B (exhaled air) turns milky while tube A (inhaled air) stays clear, the exhaled air has more carbon dioxide. She should take equal amounts of fresh lime water, pass air for the same time in both tubes, and repeat the experiment a few times.

Sample answer — good practices for oral hygiene:

Sample answer — habits: eat meals at proper times; chew food well and eat slowly (mindful eating); do not overeat; drink enough water; wash hands before eating; stay physically active; avoid too much fried and packaged food.

Sample answer — foods:

How to do this project: take a stiff cardboard sheet as the base and draw a faint human outline on it. Roll and shape coloured clay for each organ, press it into place, then write the names on black paper strips in white ink and pin them beside each organ with a thread leader.

Air quality tells how clean or polluted the air is. AQI (Air Quality Index) is a number from 0 to 500 that tells how polluted the air is on a given day; the higher the AQI, the more polluted the air.

Sample findings: farmers breathe dust and smoke from burning crop waste, factory workers breathe fine dust and fumes, and street vendors breathe vehicle smoke all day. This causes coughing, breathlessness and, over years, lung damage.

Box breathing has four equal steps, like the four sides of a square: breathe in (count 4) → hold (4) → breathe out (4) → hold (4), and repeat.

Benefits: it calms the mind and reduces nervousness, improves concentration, makes breathing slow, deep and regular, helps sleep, and can be done anywhere without any equipment.

A bird’s respiratory system gets more oxygen out of less air:

• Besides lungs, birds have air sacs that store air and keep it moving through the lungs.
• Air flows through a bird’s lungs in one direction, so fresh air reaches the lungs both while breathing in and while breathing out.
• Their lungs have very fine air tubes in close contact with blood, so birds take a larger share of the oxygen from each breath.