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Life Processes in Animals

NCERT Class 7 · Science Based on NCERT Class 7 Science textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explores the essential life processes of nutrition and respiration in animals, focusing on how food is broken down and how energy is released. It explains the journey of food through the human digestive system, from the mouth to the anus, and the mechanism of breathing and respiration. The big idea is that all animals carry out these processes, but the structures and methods vary based on their habitat and diet. A student must understand that digestion breaks down complex food into simpler forms, and respiration uses oxygen to release energy from glucose.
Key Concepts (27)
Life processes
Processes essential for the survival of living beings, such as nutrition, respiration, excretion, and reproduction.
e.g. Eating food (nutrition) and breathing (respiration) are life processes that keep us alive.
Alimentary canal
A long tube in the body through which food passes, starting from the mouth and ending at the anus, where digestion and absorption occur.
e.g. The alimentary canal includes the mouth, oesophagus, stomach, small intestine, large intestine, and anus.
Mechanical digestion
The initial breakdown of food into smaller pieces by processes like crushing and chewing, mainly in the mouth.
e.g. Chewing a chapati with your teeth breaks it into smaller pieces, which is mechanical digestion.
Saliva
A digestive juice secreted in the mouth that helps break down starch into sugar.
e.g. When you chew a piece of boiled rice for a long time, it tastes sweet because saliva breaks down the starch into sugar.
Digestion
The process of breaking down complex food components into simpler forms that the body can use.
e.g. The stomach breaks down proteins into simpler components using digestive juice.
Oesophagus
A long, flexible tube that connects the mouth to the stomach, also called the food pipe.
e.g. After swallowing, food moves down the oesophagus into the stomach.
Stomach
A muscular organ where food is churned and mixed with digestive juice, acid, and mucus to break down proteins and kill bacteria.
e.g. The stomach's acid helps digest protein from dal and kills harmful bacteria in food.
Small intestine
The longest part of the alimentary canal (about 6 metres) where most digestion and absorption of nutrients occur.
e.g. Digested nutrients from khichdi are absorbed through the walls of the small intestine into the blood.
Liver
An organ that secretes bile, which neutralises acids and breaks down fats into tiny droplets.
e.g. Bile from the liver helps digest the oil in a samosa.
Pancreas
An organ that secretes pancreatic juice, which neutralises acids and breaks down carbohydrates, proteins, and fats.
e.g. Pancreatic juice helps digest the carbohydrates in a roti.
Absorption
The process by which digested nutrients pass from the small intestine into the blood.
e.g. Glucose from digested food is absorbed into the blood through the finger-like projections in the small intestine.
Large intestine
A wider but shorter part of the alimentary canal (about 1.5 metres) that absorbs water and salts from undigested food, forming stool.
e.g. After digestion, water from leftover food is absorbed in the large intestine, making the waste semi-solid.
Rectum
The lower part of the large intestine where stool is stored until it is expelled.
e.g. The rectum holds the waste until you go to the toilet.
Egestion
The process of expelling undigested waste (stool) from the body through the anus.
e.g. After digestion, the body removes waste through egestion.
Rumination
The process in which grass-eating animals like cows partially chew grass, swallow it, bring it back to the mouth, and chew it thoroughly.
e.g. A cow spends about 8 hours a day chewing its food through rumination.
Ruminants
Animals that carry out rumination, such as cows and buffaloes.
e.g. Cows and goats are ruminants that digest grass by rumination.
Gizzard
A chamber in birds that helps break down food by contraction and relaxation, often with the help of small stones (grit).
e.g. Birds swallow small stones that help the gizzard grind food since they have no teeth.
Breathing
The physical process of inhaling and exhaling air to bring oxygen into the body and remove carbon dioxide.
e.g. When you take a deep breath before running, you are breathing in air.
Respiration
The chemical process inside the body where glucose is broken down using oxygen to release energy, producing carbon dioxide and water.
e.g. When you run, respiration in your cells uses oxygen to release energy from glucose so you can move.
Respiratory system
The system in the body responsible for breathing and respiration, including nostrils, nasal passages, windpipe, lungs, and alveoli.
e.g. The respiratory system helps you breathe in oxygen and breathe out carbon dioxide.
Nostrils
A pair of nasal openings through which air is inhaled and exhaled.
e.g. You should breathe through your nostrils because tiny hairs there trap dust.
Nasal passages
Small passages inside the nose where tiny hairs and mucus trap dust and dirt from inhaled air.
e.g. When you breathe through your nose, the nasal passages filter the air.
Windpipe
The tube that carries air from the nasal passages to the lungs.
e.g. Air travels down the windpipe to reach the lungs.
Alveoli
Small balloon-like sacs in the lungs where the exchange of oxygen and carbon dioxide occurs.
e.g. Oxygen from the air passes into the blood through the thin walls of the alveoli.
Diaphragm
A dome-shaped muscle below the lungs that moves downwards during inhalation and upwards during exhalation to help breathing.
e.g. When you inhale, your diaphragm moves down, increasing chest space and drawing air in.
Gills
Specialised structures in aquatic animals like fish that allow exchange of oxygen and carbon dioxide between blood and water.
e.g. Fish breathe through gills, which extract oxygen dissolved in water.
Circulatory system
The system that transports nutrients, oxygen, and other substances throughout the body, including the heart, blood, and blood vessels.
e.g. The heart pumps blood to carry oxygen from the lungs to all parts of the body.
How It Works
Digestion in humans
  1. Food enters the mouth, where teeth crush and chew it (mechanical digestion).
  2. Saliva in the mouth breaks down starch into sugar (chemical digestion).
  3. The tongue mixes food with saliva and pushes it into the oesophagus.
  4. The oesophagus uses wave-like contractions (peristalsis) to push food into the stomach.
  5. In the stomach, walls churn food and mix it with digestive juice, acid, and mucus; proteins are broken down, and bacteria are killed.
  6. Partially digested food moves to the small intestine, where bile from the liver and pancreatic juice from the pancreas further break down fats, proteins, and carbohydrates.
  7. Digestive juice from the small intestine wall completes digestion into simpler forms.
  8. Nutrients are absorbed through finger-like projections (villi) in the small intestine into the blood.
  9. Undigested food moves to the large intestine, where water and salts are absorbed, forming semi-solid stool.
  10. Stool is stored in the rectum and expelled through the anus (egestion).
💡 Students often confuse the small intestine and large intestine: the small intestine is longer (6 m) but narrower, while the large intestine is shorter (1.5 m) but wider.
Mechanism of breathing
  1. Inhalation: The ribs move up and outwards, and the diaphragm moves downwards, increasing chest space.
  2. Air enters the lungs through the nostrils, nasal passages, and windpipe, filling the alveoli.
  3. In the alveoli, oxygen passes into the blood, and carbon dioxide from the blood moves into the alveoli.
  4. Exhalation: The ribs move down and inwards, and the diaphragm moves upwards, reducing chest space.
  5. Air rich in carbon dioxide is pushed out of the lungs through the windpipe and nostrils.
💡 Students often think that during inhalation, the diaphragm moves up; it actually moves down. The rubber sheet in the model represents the diaphragm.
Respiration (cellular)
  1. Glucose from digested food is transported to cells via the blood.
  2. Oxygen from inhaled air is transported to cells via the blood.
  3. In cells, glucose is broken down using oxygen to release energy.
  4. Carbon dioxide and water are produced as waste products.
  5. Carbon dioxide is carried back to the lungs and exhaled.
💡 Respiration is a chemical process inside cells, not the same as breathing. The word equation is: Glucose + Oxygen → Carbon dioxide + Water + Energy.
Rumination in grass-eating animals
  1. The animal partially chews grass and swallows it into the stomach (rumen).
  2. Partial digestion occurs in the stomach.
  3. The partially digested food is brought back to the mouth.
  4. The animal chews the food thoroughly (rumination).
  5. The thoroughly chewed food passes down the alimentary canal for further digestion.
💡 Rumination is not the same as normal chewing; it is a two-step process where food is brought back to the mouth for re-chewing.
Gas exchange in fish
  1. Water enters the fish's mouth and passes over the gills.
  2. Gills are richly supplied with blood vessels.
  3. Oxygen dissolved in water passes into the blood.
  4. Carbon dioxide from the blood passes into the water.
  5. Water exits the fish's body.
💡 Fish do not breathe air; they extract oxygen dissolved in water using gills.
Exam Traps — Don't Make These Mistakes
⚠ Confusing breathing with respiration
✗ Breathing and respiration are the same process.
→ Breathing is a physical process of inhaling and exhaling air, while respiration is a chemical process inside cells that uses oxygen to break down glucose and release energy.
✓ Breathing is the physical process of taking in oxygen and giving out carbon dioxide, while respiration is the chemical process in cells where glucose is broken down with oxygen to release energy.
⚠ Mixing up small and large intestine lengths
✗ The large intestine is longer than the small intestine.
→ The small intestine is about 6 metres long, while the large intestine is about 1.5 metres long. The large intestine is called 'large' because it is wider, not longer.
✓ The small intestine is the longest part of the alimentary canal (about 6 metres), while the large intestine is shorter (about 1.5 metres) but wider.
⚠ Incorrect diaphragm movement during inhalation
✗ During inhalation, the diaphragm moves upwards.
→ During inhalation, the diaphragm moves downwards, increasing the space in the chest cavity and allowing air to enter the lungs.
✓ During inhalation, the diaphragm moves downwards, and the ribs move up and outwards, increasing chest space and drawing air in.
⚠ Thinking all animals breathe the same way
✗ All animals breathe through lungs like humans.
→ Different animals have different breathing mechanisms: fish use gills, earthworms use moist skin, frogs use skin and lungs, and birds have lungs adapted for high altitudes.
✓ Animals have different breathing organs: humans and land animals use lungs, fish use gills, earthworms use moist skin, and frogs use both skin and lungs.
⚠ Confusing the role of bile and pancreatic juice
✗ Bile breaks down fats completely.
→ Bile only breaks down fats into tiny droplets (emulsification), making digestion easier, but it does not chemically digest fats. Pancreatic juice and intestinal juice complete fat digestion.
✓ Bile from the liver breaks down fats into tiny droplets (emulsification), while pancreatic juice and intestinal juice chemically digest fats into simpler forms.
Compare & Contrast
Nature of the process
Breathing
Respiration
Breathing is a physical process of inhaling and exhaling air, while respiration is a chemical process inside cells that uses oxygen to break down glucose and release energy.
Length and function
Small intestine
Large intestine
The small intestine is longer (about 6 m) and is the main site for digestion and absorption of nutrients, while the large intestine is shorter (about 1.5 m) but wider, and absorbs water and salts from undigested food.
Composition of oxygen and carbon dioxide
Inhaled air
Exhaled air
Inhaled air contains about 21% oxygen and 0.04% carbon dioxide, while exhaled air contains about 16-17% oxygen and 4-5% carbon dioxide.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 SA (3 marks), 1 LA (5 marks) — typically from digestion and respiration topics.
Most asked: Human digestive system and the journey of food · Role of saliva in starch digestion · Difference between breathing and respiration · Mechanism of breathing (role of diaphragm) · Gas exchange in alveoli · Rumination in grass-eating animals
Don't skip: Explain the process of digestion in humans with a diagram of the alimentary canal.; Differentiate between breathing and respiration with the word equation for respiration.; Describe the mechanism of breathing, including the role of the diaphragm.
One-Line Revision (read aloud before the exam)
  1. Life processes include nutrition, respiration, excretion, and reproduction.
  2. The alimentary canal is a long tube from the mouth to the anus where digestion occurs.
  3. Saliva in the mouth breaks down starch into sugar, making chewed chapati taste sweet.
  4. The stomach uses acid to kill bacteria and digestive juice to break down proteins.
  5. The small intestine is the longest part of the alimentary canal (about 6 metres) where most absorption occurs.
  6. Bile from the liver breaks down fats into tiny droplets, and pancreatic juice digests carbohydrates, proteins, and fats.
  7. The large intestine absorbs water and salts from undigested food, forming stool.
  8. Rumination is the process where cows partially chew grass, swallow it, and later bring it back to the mouth for thorough chewing.
  9. Breathing is a physical process of inhaling and exhaling air, while respiration is a chemical process that releases energy from glucose.
  10. The diaphragm moves downwards during inhalation and upwards during exhalation.
  11. Alveoli are tiny sacs in the lungs where oxygen and carbon dioxide are exchanged.
  12. Fish breathe through gills, earthworms through moist skin, and frogs through skin and lungs.
  13. The word equation for respiration is: Glucose + Oxygen → Carbon dioxide + Water + Energy.
  14. Inhaled air has about 21% oxygen and 0.04% carbon dioxide; exhaled air has about 16-17% oxygen and 4-5% carbon dioxide.

MCQs — 10 Questions with Answers

Q1. Which of the following is an example of mechanical digestion?

  • A. Chewing food with teeth ✓
  • B. Saliva breaking down starch
  • C. Stomach acid breaking down proteins
  • D. Villi absorbing nutrients

Answer: A — Mechanical digestion is the physical breakdown of food by chewing, while others are chemical digestion or absorption.

Q2. What does iodine solution turn blue-black to detect?

  • A. Proteins
  • B. Fats
  • C. Starch ✓
  • D. Sugars

Answer: C — Iodine specifically reacts with starch molecules to produce a blue-black colour, making it useful to test for starch presence.

Q3. The alimentary canal is a long tube that starts from the mouth and ends at which part?

  • A. Stomach
  • B. Small intestine
  • C. Anus ✓
  • D. Large intestine

Answer: C — The alimentary canal is the entire digestive tract beginning at the mouth and ending at the anus where waste is expelled.

Q4. How long is the small intestine in a human body?

  • A. About 1.5 metres
  • B. About 6 metres ✓
  • C. About 3 metres
  • D. About 10 metres

Answer: B — The small intestine is approximately 6 metres long, almost twice the height of a classroom, despite being called 'small'.

Q5. Ravi chewed a piece of roti for 30 seconds and then tested it with iodine. What would most likely happen?

  • A. Strong blue-black colour appears
  • B. No colour change or very light blue-black colour ✓
  • C. Red colour appears
  • D. Yellow colour appears

Answer: B — Saliva in the mouth breaks down starch in roti into sugars, so iodine would not react strongly or at all.

Q6. Which organ secretes a substance that breaks down fats into tiny droplets in the small intestine?

  • A. Pancreas
  • B. Liver ✓
  • C. Stomach
  • D. Large intestine

Answer: B — The liver secretes bile, which is basic in nature and breaks fats into smaller droplets for easier digestion.

Q7. Priya has celiac disease. Which of these Indian grains should she avoid?

  • A. Ragi and bajra
  • B. Wheat and barley ✓
  • C. Jowar and maize
  • D. Rice and millet

Answer: B — Wheat and barley contain gluten which damages the small intestine lining in celiac disease; ragi, bajra, and jowar are naturally gluten-free.

Q8. The finger-like projections in the small intestine increase surface area mainly for which process?

  • A. Mechanical digestion
  • B. Chemical digestion
  • C. Nutrient absorption into blood ✓
  • D. Water absorption

Answer: C — Villi in the small intestine increase surface area specifically to allow digested nutrients to be absorbed efficiently into the bloodstream.

Q9. During digestion, what is the main reason stomach acid does NOT damage the stomach itself?

  • A. The acid is very weak
  • B. Mucus protects the stomach lining ✓
  • C. Food absorbs all the acid
  • D. The stomach wall is made of steel-like material

Answer: B — The stomach secretes mucus that coats and protects its inner lining from the strong acid that breaks down proteins.

Q10. If a person does not eat enough fibre-rich foods like vegetables and whole grains, what is most likely to happen?

  • A. The small intestine will become longer
  • B. The liver will stop producing bile
  • C. The large intestine cannot function properly and stool becomes hard ✓
  • D. Saliva production will increase

Answer: C — Fibre helps the large intestine absorb water properly and form soft stool; without it, the stool becomes hard and constipation occurs.

Flashcards

What is mechanical digestion?

Breaking down food into smaller pieces by chewing and crushing with teeth.

Why does chapati taste sweet when chewed for 30-60 seconds?

Saliva contains an enzyme that breaks down starch into sugar.

Name the three sources of digestive juice in the small intestine.

Inner lining of small intestine itself, liver (bile), and pancreas (pancreatic juice).

What are the finger-like projections in the small intestine called?

Villi—they increase surface area for nutrient absorption into blood.

How does food move through the food pipe (oesophagus)?

The walls contract and relax in wave-like motions called peristalsis.

What is the role of mucus in the stomach?

It protects the stomach lining from being damaged by acid.

Why is the large intestine called 'large' if the small intestine is longer?

The large intestine is wider than the small intestine, not longer.

What is egestion?

The process of expelling undigested waste material through the anus.

What is the semi-solid waste in the large intestine called?

Stool—formed after water and salts are absorbed from undigested food.

Which organ secretes bile and why?

The liver secretes bile to neutralise stomach acid and break down fats.

Important Board Questions

What is digestion? [1 mark]

Define as process of breaking complex food into simpler forms. Mention it happens in alimentary canal.

Describe the role of saliva in the mouth during digestion. [2 marks]

Saliva breaks down starch into sugar (chemical action) AND makes food soft and moist for easy swallowing (mechanical aid). Mention enzyme role.

Explain why the small intestine, despite its name, is the longest part of the alimentary canal. How does its structure help in nutrient absorption? [3 marks]

Small intestine is ~6 metres long (longer than large intestine which is 1.5m). It is called 'small' because it is narrower. Villi increase surface area for absorption of digested nutrients into blood vessels in its walls.

Draw and label a diagram of the human digestive system. Describe the complete journey of food from the mouth to the anus, mentioning what happens at each major part of the alimentary canal. [5 marks]

Draw diagram with labels: mouth, food pipe (oesophagus), stomach, small intestine, large intestine, liver, pancreas, anus, rectum. Describe: mouth (mechanical + chemical digestion), food pipe (peristalsis), stomach (protein breakdown + acid), small intestine (final digestion + absorption), large intestine (water absorption, stool formation), anus (egestion).

Assertion-Reason Questions for Life Processes in Animals

Q1. Assertion (A):

Saliva plays an important role in the initial digestion of food.

Reason (R):

Saliva contains a digestive juice that breaks down starch into simple sugars and also moistens the food.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true, and the reason correctly explains why saliva is important for initial digestion. Activity 9.1 proves that saliva breaks down starch into sugars, and the textbook states that saliva moistens food for easy swallowing. The reason fully supports the assertion.

Q2. Assertion (A):

The food pipe (oesophagus) allows food to move from the mouth to the stomach even when a person is inverted or upside down.

Reason (R):

Gravity is the only force responsible for moving food through the food pipe.

Answer: C — A is true but R is false — The assertion is true—food can move through the food pipe even upside down. However, the reason is false. The textbook states that wave-like muscular contractions and relaxations (peristalsis) of the food pipe walls push food downward, not gravity alone. Gravity is not the only force; muscular movement is primary.

Q3. Assertion (A):

The stomach produces mucus as part of its digestive secretions.

Reason (R):

Mucus in the stomach absorbs nutrients from the food.

Answer: C — A is true but R is false — The assertion is true—the textbook clearly states that the stomach secretes mucus along with digestive juice and acid. However, the reason is false. Mucus protects the stomach lining from acid damage; it does not absorb nutrients. Nutrient absorption occurs in the small intestine, not the stomach. The reason contradicts the textbook's explanation of mucus function.

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Case-Based Questions (CBQ) for Life Processes in Animals

Case Study:

Rahul conducted an experiment similar to Activity 9.1 with three test tubes. Test tube A contained uncooked rice, test tube B contained boiled rice chewed for 30 seconds, and test tube C contained boiled rice chewed for 2 minutes. He added water to each tube and then added iodine solution. Test tube A remained blue-black, test tube B showed only a slight blue color, and test tube C showed no blue color change. Rahul concluded that longer chewing time results in more complete breakdown of starch.

Q1. Why did test tube A remain blue-black after adding iodine?

  • A. Because uncooked rice contains more starch than boiled rice
  • B. Because starch in the uncooked rice was not broken down by saliva ✓
  • C. Because uncooked rice reacts differently with iodine than boiled rice
  • D. Because the iodine solution was stronger in test tube A

Answer: B

Q2. What does the absence of blue color in test tube C indicate?

  • A. The rice was spoiled after chewing for 2 minutes
  • B. All or nearly all the starch was broken down into sugars by saliva during the 2-minute chewing period ✓
  • C. Iodine stopped working after being in contact with rice for too long
  • D. Two minutes of chewing is harmful to the rice's structure

Answer: B

Q3. Which observation best supports Rahul's conclusion about longer chewing time?

  • A. Test tube B and C both showed less starch than test tube A, with test tube C showing less than test tube B ✓
  • B. Test tube A turned blue-black the fastest
  • C. Boiled rice reacts differently with iodine than uncooked rice
  • D. The amount of water added was the same in all three test tubes

Answer: A

Q4. If Rahul wanted to test whether time affects the digestion of protein as well as starch, which change to the experiment would be most appropriate?

  • A. Use egg white instead of rice and test for protein breakdown over different chewing times ✓
  • B. Use only boiled rice and increase the water amount in each test tube
  • C. Repeat the same experiment but use uncooked rice in all test tubes
  • D. Add stomach digestive juice to the test tubes instead of iodine

Answer: A

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