Class 7 Science NCERT Notes – Chapter 9: Life Processes in Animals (PDF, MindMap, Q&A, Quizzes)

Chapter 9 (Science): Life Processes in Animals – CBSE Class 7 NCERT Science Detailed Study Notes.

1. Introduction to Life Processes

Life processes are the essential functions that all living beings perform to survive. These processes, which work in coordination, include:

• Nutrition
• Respiration
• Excretion
• Reproduction
• Circulation

This chapter focuses in detail on nutrition and respiration.

2. Nutrition and Digestion

Nutrition is the process by which animals obtain and use food to gain energy for various life processes. Food contains complex components like carbohydrates, proteins, and fats, which must be broken down into simpler forms for the body to use.

2.1 The Human Digestive System

The process of breaking down complex food components into simpler forms is called digestion. This occurs within a long tube called the alimentary canal, which starts at the mouth and ends at the anus.

The Journey of Food:

1. Mouth (Mouth Cavity):
   • Mechanical Digestion: The process begins here. Teeth crush and chew food into smaller pieces.
   • Chemical Digestion: Saliva, a digestive juice, is secreted in the mouth. Saliva moistens the food and contains an enzyme that begins breaking down complex carbohydrates (starch) into simpler sugars. This is why starchy foods like rice or chapati taste sweet after being chewed for a while.
2. Oesophagus (Food Pipe):
   • The tongue pushes the softened, partially digested food into the oesophagus.
   • The walls of the food pipe contract and relax in a wave-like motion, pushing the food forward into the stomach. This movement occurs throughout the alimentary canal.
3. Stomach:
   • The walls of the stomach churn the food, mixing it with secretions from its inner lining.
   • These secretions include digestive juice, acid, and mucus.
   • The discovery of the stomach’s function was notably advanced by Dr. William Beaumont, who observed digestion through a permanent hole in the stomach of a man named Alexis St. Martin in 1822.
4. Small Intestine:
   • This is the longest part of the alimentary canal, measuring almost 6 meters in length.
   • It receives digestive secretions from three sources: its own inner lining, the liver, and the pancreas.
   • Liver: Secretes bile, which is mildly basic. Bile neutralizes the acid from the stomach and breaks down large fat globules into tiny droplets, making them easier to digest.
   • Pancreas: Secretes pancreatic juice, which is also basic. It helps neutralize acid and breaks down carbohydrates, proteins, and fats.
   • The final breakdown of fats, proteins, and carbohydrates into their simplest forms occurs here.
   • Absorption: The inner walls of the small intestine have thousands of thin, finger-like projections. These projections vastly increase the surface area for the efficient absorption of digested nutrients into the blood vessels within the intestinal walls.
5. Large Intestine:
   • Undigested food moves from the small intestine to the large intestine.
   • It is about 1.5 meters long but is wider than the small intestine.
   • Its primary function is to absorb water and some salts from the remaining undigested food.
   • This process turns the waste into a semi-solid form called stool. The large intestine also contains beneficial bacteria that help break down undigested fibre and produce essential nutrients.
6. Rectum and Anus:
   • The stool is stored in the rectum, the lower part of the large intestine.
   • It is finally expelled from the body through the anus. This process is called egestion.

2.2 Digestion in Other Animals

• Ruminants (Grass-eating animals like cows): These animals partially chew their food and swallow it. Later, this partially digested food is brought back to the mouth for thorough chewing. This process is called rumination.
• Birds: Birds lack teeth. They have a muscular chamber called a gizzard that grinds food, often with the help of small stones (grit) that the bird swallows.

3. Respiration in Animals

Respiration is the chemical process by which the body breaks down nutrients (like glucose from food) using oxygen to release usable energy. Breathing is the physical process that facilitates respiration.

3.1 The Human Respiratory System

The respiratory system is the specific pathway for breathing.

The Pathway of Air:

1. Nostrils and Nasal Passages: Air is inhaled through the nostrils and enters the nasal passages. Tiny hairs and mucus in these passages trap dust and dirt, filtering the air.
2. Windpipe (Trachea): The filtered air travels down the windpipe.
3. Lungs and Alveoli: The windpipe branches into two tubes, each entering a lung. Inside the lungs, these tubes divide into smaller and finer branches, ending in millions of tiny, balloon-like air sacs called alveoli. The lungs are protected by the rib cage.
4. Gas Exchange: The alveoli have very thin walls and are surrounded by a network of fine blood vessels. Here, oxygen from the inhaled air passes into the blood, while carbon dioxide (a waste product) passes from the blood into the alveoli to be exhaled.

The Chemical Process of Respiration: The oxygen transported by the blood is used by the body’s cells to break down glucose. This chemical reaction releases the energy needed for all bodily functions. Glucose + Oxygen → Carbon dioxide + Water + Energy

Breathing vs. Respiration:

• Breathing: A physical process of inhaling and exhaling air.
• Respiration: A chemical process inside cells that releases energy from food.

Mechanism of Breathing:

• Inhalation (Breathing In): The ribs move up and outwards, and the diaphragm (a dome-shaped muscle below the lungs) moves downwards. This increases the space in the chest cavity, causing air to rush into the lungs.
• Exhalation (Breathing Out): The ribs move down and inwards, and the diaphragm moves upwards. This reduces the space in the chest cavity, pushing air out of the lungs.

3.2 Respiration in Other Animals

Different animals have adapted different mechanisms for breathing based on their habitat.

• Fish: Use specialized structures called gills, which are richly supplied with blood vessels, to extract dissolved oxygen from water.
• Amphibians (Frogs): Have multiple methods. Tadpoles breathe through gills. Adult frogs use lungs on land and can also exchange gases through their moist skin when in water.
• Earthworms: Breathe through their moist skin.
• Birds, Elephants, Lizards, etc.: Breathe through lungs, similar to humans, though the structures may differ.

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Quiz and Q&A Section

Short-Answer Questions (25 Questions)

Answer each question in 2-3 complete sentences.

1. What are life processes, and can you name four examples?
2. What is the primary purpose of the digestive system?
3. Describe the process of mechanical digestion that occurs in the mouth.
4. What is the role of saliva in the digestion of starchy foods like chapati?
5. How does food travel from the mouth to the stomach through the oesophagus?
6. What three substances are secreted by the stomach’s inner lining to aid digestion?
7. Why is the small intestine considered the longest part of the alimentary canal?
8. Describe the function of bile, which is secreted by the liver.
9. What is the role of pancreatic juice in the small intestine?
10. How are digested nutrients absorbed in the small intestine?
11. What is the main function of the large intestine?
12. Explain the process of egestion.
13. What is rumination, and which animals perform it?
14. How do birds, which lack teeth, break down their food?
15. What is the difference between breathing and respiration?
16. Trace the path of air from the nostrils to the alveoli in the human respiratory system.
17. How do the nasal passages help in cleaning the air we breathe?
18. What are alveoli, and what critical process occurs there?
19. Describe the movements of the ribs and diaphragm during inhalation.
20. Describe the movements of the ribs and diaphragm during exhalation.
21. Write the word equation for the chemical process of respiration.
22. How does the composition of inhaled air differ from exhaled air in terms of oxygen and carbon dioxide?
23. How do fish breathe underwater?
24. Explain how adult frogs are adapted to breathe both on land and in water.
25. How do earthworms perform gas exchange?

Multiple-Choice Questions (20 Questions)

Choose the best answer for each question.

1. Which of the following is NOT listed as a life process in the text? A) Nutrition B) Respiration C) Photosynthesis D) Excretion
2. The initial breakdown of food by crushing and chewing is called: A) Chemical digestion B) Mechanical digestion C) Absorption D) Egestion
3. Saliva contains a digestive juice that breaks down which complex component? A) Protein B) Fat C) Starch D) Fibre
4. The wave-like movement that pushes food through the alimentary canal is caused by: A) Gravity B) The tongue C) Contraction and relaxation of the canal walls D) The churning of the stomach
5. Which organ secretes bile? A) Pancreas B) Stomach C) Small intestine D) Liver
6. The primary site for the absorption of digested nutrients is the: A) Stomach B) Large intestine C) Small intestine D) Oesophagus
7. What is the approximate length of the human small intestine? A) 1.5 meters B) 3 meters C) 6 meters D) 9 meters
8. The main function of the large intestine is to absorb: A) Nutrients and fats B) Water and some salts C) Proteins and carbohydrates D) Sugars and starches
9. The process of expelling stool from the body is known as: A) Digestion B) Rumination C) Absorption D) Egestion
10. Animals like cows that bring partially digested food back to the mouth to chew are called: A) Avians B) Ruminants C) Amphibians D) Gizzards
11. What structure in a bird’s digestive system helps grind food? A) Rumen B) Gizzard C) Alveoli D) Bile duct
12. In the human respiratory system, gas exchange occurs in the: A) Windpipe B) Nasal passages C) Diaphragm D) Alveoli
13. During inhalation, the diaphragm: A) Moves upward B) Moves downward C) Relaxes completely D) Stays stationary
14. Exhaled air contains more of which gas compared to inhaled air? A) Oxygen B) Nitrogen C) Carbon dioxide D) Water vapor
15. Respiration is a chemical process that uses oxygen to break down: A) Water B) Carbon dioxide C) Glucose D) Bile
16. What specialized structures do fish use for breathing? A) Lungs B) Gills C) Moist skin D) Alveoli
17. Adult frogs can breathe through their lungs and their: A) Gills B) Gizzard C) Skin D) Nostrils
18. In the experiment with lime water, what causes it to turn milky? A) The presence of oxygen B) The presence of water C) The presence of nitrogen D) The presence of carbon dioxide
19. The finger-like projections in the small intestine serve to: A) Secrete digestive juices B) Increase surface area for absorption C) Move food along the canal D) Store undigested waste
20. The rib cage’s primary function in the respiratory system is to: A) Help churn food B) Secrete mucus C) Protect the lungs D) Contract and relax for breathing

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Answer Keys

Short-Answer Questions Answer Key

1. Life processes are essential functions for the survival of living beings. Four examples are nutrition, respiration, excretion, and reproduction.
2. The primary purpose of the digestive system is to break down complex food components like carbohydrates, proteins, and fats into simpler forms. These simpler forms can then be absorbed and used by the body for energy, growth, and repair.
3. Mechanical digestion in the mouth involves the teeth breaking down food into smaller pieces. This is achieved through the processes of crushing and chewing, which increases the surface area of the food for chemical digestion.
4. Saliva moistens food and contains a digestive juice that starts the chemical breakdown of starch, a type of carbohydrate. This enzyme converts the starch into simpler sugars, which is why starchy food tastes sweet after prolonged chewing.
5. After being swallowed, food is pushed down the oesophagus by a wave-like motion. The walls of the food pipe gently contract and relax, pushing the food forward into the stomach.
6. The inner lining of the stomach secretes digestive juice, acid, and mucus. These substances mix with the churned food to continue the digestive process.
7. The small intestine is the longest part of the alimentary canal, measuring almost 6 meters. This extensive length provides a large surface area and sufficient time for the complete digestion and absorption of nutrients.
8. Bile is a mildly basic fluid that neutralizes the acidic food coming from the stomach. It also plays a crucial role in fat digestion by breaking down large fat globules into tiny droplets, making it easier for enzymes to act on them.
9. Pancreatic juice, secreted by the pancreas, is basic in nature and helps neutralize stomach acid. It contains enzymes that break down carbohydrates, proteins, and fats into simpler forms.
10. The inner lining of the small intestine is covered with thousands of finger-like projections. These structures increase the surface area, allowing digested nutrients to efficiently pass into the blood vessels within the intestinal walls.
11. The main function of the large intestine is to absorb most of the remaining water and some salts from undigested food. This process solidifies the waste material into stool.
12. Egestion is the final step of the digestive process where semi-solid waste, or stool, is eliminated from the body. The stool is stored in the rectum until it is expelled through the anus.
13. Rumination is the process where partially chewed and swallowed food is brought back from the stomach to the mouth for more thorough chewing. Animals that perform this, such as cows and buffaloes, are called ruminants.
14. Birds have a muscular chamber in their digestive tract called a gizzard. The gizzard’s walls contract and relax to grind food, a process often aided by small stones (grit) that the bird swallows.
15. Breathing is the physical process of inhaling air into the lungs and exhaling it out. Respiration is the chemical process that occurs inside the body’s cells, where oxygen is used to break down glucose to release energy.
16. Air enters through the nostrils into the nasal passages, then travels down the windpipe, which branches into the two lungs. Inside the lungs, the air moves through progressively smaller branches until it reaches the tiny air sacs called alveoli.
17. The nasal passages contain tiny hairs and are lined with mucus. These features work together to trap dust, dirt, and other particles from the inhaled air, effectively filtering it before it reaches the lungs.
18. Alveoli are small, balloon-like sacs at the end of the respiratory passages in the lungs. They are the site of gas exchange, where oxygen from the air passes into the blood and carbon dioxide from the blood passes into the air.
19. During inhalation, the ribs move up and outwards, while the diaphragm contracts and moves downwards. This combined movement increases the volume of the chest cavity, allowing the lungs to expand and draw in air.
20. During exhalation, the ribs move down and inwards, while the diaphragm relaxes and moves upwards into its dome shape. This decreases the volume of the chest cavity, compressing the lungs and forcing air out.
21. The word equation for respiration is: Glucose + Oxygen → Carbon dioxide + Water + Energy.
22. Inhaled air contains approximately 21% oxygen. Exhaled air has a lower concentration of oxygen (about 16-17%) and a significantly higher concentration of carbon dioxide (about 4-5%).
23. Fish breathe using gills, which are specialized structures with a rich supply of blood vessels. As water flows over the gills, dissolved oxygen passes into the blood, and carbon dioxide passes from the blood into the water.
24. Adult frogs use lungs for breathing when on land, similar to other terrestrial animals. When in water, they can perform gas exchange directly through their moist skin, allowing them to absorb oxygen from the water.
25. Earthworms use their moist skin for the exchange of gases. Oxygen diffuses from the surrounding air or soil into the blood vessels just beneath the skin, and carbon dioxide diffuses out.

Multiple-Choice Questions Answer Key

1. C) Photosynthesis
2. B) Mechanical digestion
3. C) Starch
4. C) Contraction and relaxation of the canal walls
5. D) Liver
6. C) Small intestine
7. C) 6 meters
8. B) Water and some salts
9. D) Egestion
10. B) Ruminants
11. B) Gizzard
12. D) Alveoli
13. B) Moves downward
14. C) Carbon dioxide
15. C) Glucose
16. B) Gills
17. C) Skin
18. D) The presence of carbon dioxide
19. B) Increase surface area for absorption
20. C) Protect the lungs

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Essay Questions (10 Questions with Answers)

1. Trace the complete journey of a meal containing carbohydrates, proteins, and fats through the human alimentary canal. Describe the key digestive events that occur in the mouth, stomach, and small intestine.
   • Answer: The journey of a meal begins in the mouth, where mechanical digestion starts as teeth chew and crush the food. Simultaneously, chemical digestion of carbohydrates begins as saliva mixes with the food, its enzymes breaking down starches into simpler sugars. The food is then swallowed and travels down the oesophagus via wave-like muscular contractions. In the stomach, the food is churned and mixed with acidic digestive juices and mucus. Here, the digestion of proteins begins. The partially digested, acidic food then moves into the small intestine. This is where the final and most significant digestion occurs. The small intestine receives bile from the liver, which emulsifies fats, and pancreatic juice from the pancreas, which contains enzymes to break down carbohydrates, proteins, and fats. The walls of the small intestine also secrete digestive juices to complete the breakdown of all nutrients into their simplest forms (sugars, amino acids, fatty acids), which are then ready for absorption.
2. Explain the roles of the liver and pancreas in human digestion. Why are they considered associated parts rather than parts of the alimentary canal itself?
   • Answer: The liver and pancreas are crucial for digestion but are not part of the continuous tube (alimentary canal) that food passes through. The liver produces bile, a substance stored and released into the small intestine. Bile’s primary roles are to neutralize the acidic food mixture from the stomach and to break down large fat globules into smaller droplets, a process that makes fat digestion more efficient. The pancreas produces pancreatic juice, which is also secreted into the small intestine. This juice contains a powerful mix of enzymes that break down all three major food components: carbohydrates, proteins, and fats. Because food does not pass directly through the liver or pancreas, they are considered associated or accessory organs of the digestive system.
3. Describe the process of nutrient absorption. How is the small intestine structurally adapted for this function, and what happens to the nutrients after they are absorbed?
   • Answer: Absorption is the process where digested nutrients pass from the small intestine into the bloodstream. The small intestine is exceptionally well-adapted for this role. Its inner lining is not smooth but is covered in thousands of tiny, finger-like projections. These projections dramatically increase the surface area available for absorption. The thin walls of these projections are rich with blood vessels. Digested nutrients, now in their simplest forms, pass through these thin walls into the blood. Once in the bloodstream, the circulatory system transports these nutrients to all parts of the body, where they are used for energy, growth, and the repair of tissues.
4. Compare and contrast the digestive processes of a human and a ruminant, such as a cow. What key differences allow ruminants to digest grass effectively?
   • Answer: Both humans and ruminants have an alimentary canal for digestion, but their systems are adapted for very different diets. Humans have a single-chambered stomach and rely on enzymes to break down food. Ruminants, like cows, have a complex, multi-chambered stomach designed to digest tough plant material like grass. The key difference is the process of rumination. A cow first partially chews and swallows grass into its stomach, where it undergoes partial digestion. Later, it regurgitates this partially digested food (cud) back to the mouth for thorough chewing. This process allows for the mechanical breakdown of fibrous plant matter. Furthermore, the ruminant stomach hosts microorganisms that help break down cellulose, which humans cannot digest.
5. Explain the mechanism of breathing in humans, detailing the coordinated actions of the rib cage and diaphragm during both inhalation and exhalation.
   • Answer: Breathing is a physical process controlled by the movement of the rib cage and the diaphragm. During inhalation, the rib muscles contract, pulling the rib cage up and outwards. Simultaneously, the diaphragm, a large muscle beneath the lungs, contracts and moves downwards. These actions increase the volume of the chest cavity, which creates lower pressure inside the lungs, causing air to be drawn in. During exhalation, the process reverses. The rib muscles relax, allowing the rib cage to move down and inwards, and the diaphragm relaxes, moving back up to its dome shape. This decreases the volume of the chest cavity, increasing the pressure inside the lungs and forcing air out.
6. Distinguish between the physical process of breathing and the chemical process of respiration. Explain how these two processes are fundamentally linked and essential for survival.
   • Answer: Breathing and respiration are distinct but interconnected processes. Breathing is the physical act of moving air into and out of the lungs (inhalation and exhalation). Its purpose is to supply the body with oxygen and remove carbon dioxide waste. Respiration, on the other hand, is a chemical process that takes place within every cell of the body. In this process, oxygen delivered by the blood is used to break down glucose (from digested food) to release energy. The waste products of this chemical reaction are carbon dioxide and water. The two processes are linked because breathing provides the necessary oxygen for cellular respiration to occur, and it removes the carbon dioxide produced by respiration. Without breathing, cells would not have oxygen to produce energy, and without respiration, the oxygen from breathing would have no purpose.
7. Describe the experiment that demonstrates the difference in carbon dioxide levels between inhaled and exhaled air. What is the key indicator, and what do the results signify?
   • Answer: The experiment uses two test tubes (A and B) containing freshly prepared lime water. In test tube A, ambient air (representing inhaled air) is passed through the lime water using a syringe. In test tube B, a person exhales repeatedly into the lime water through a straw. The observation is that the lime water in test tube B turns milky or cloudy, while the lime water in test tube A shows no significant change. The key indicator is lime water, which turns milky in the presence of carbon dioxide. The results signify that the air we exhale contains a significantly higher concentration of carbon dioxide than the air we inhale, confirming that carbon dioxide is a waste product of bodily processes (respiration) that is removed through breathing.
8. How have different animals adapted their respiratory systems to their specific environments? Provide and explain at least three distinct examples from the text.
   • Answer: Animals have evolved diverse respiratory systems to suit their habitats. First, most aquatic animals, like fish, have gills. Gills are specialized structures that can extract dissolved oxygen directly from water as it flows over them, allowing the fish to live entirely underwater. Second, amphibians like adult frogs exhibit a dual adaptation; they have lungs for breathing air on land but can also absorb oxygen through their moist skin when submerged in water. Third, simpler organisms like earthworms lack complex respiratory organs and perform gas exchange directly through their moist skin, which is sufficient for their needs in damp soil environments.
9. Describe the experiment that investigates the action of saliva on starch. What is the role of the iodine solution, and what do the different color outcomes in the test tubes indicate?
   • Answer: The experiment involves two test tubes. Test tube A contains boiled rice and water, while test tube B contains boiled rice that has been chewed for 30-60 seconds and mixed with water. A few drops of iodine solution are added to both. The expected observation is that the contents of test tube A turn a blue-black color, while test tube B either shows no color change or only a very light blue-black color. The iodine solution serves as an indicator for the presence of starch, turning blue-black when it reacts with it. The result in test tube A confirms starch is present in boiled rice. The lack of color change in test tube B indicates that the saliva from chewing broke down the starch into sugars, which do not react with iodine.
10. Smoking is described as being extremely harmful. Based on the text, explain the risks of smoking to the smoker and the risks of passive smoking to non-smokers.
    • Answer: According to the text, smoking is extremely harmful because it directly damages the lungs and significantly increases the risk of serious diseases like lung cancer and other respiratory illnesses. It can lead to persistent coughing and more frequent infections. The harm extends beyond the smoker. Smoking releases toxic chemicals into the air, which poses a risk to non-smokers who inhale this polluted air. This is known as passive smoking and is described as being especially dangerous for vulnerable groups such as children, pregnant women, and the elderly.

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Glossary of Key Terms

Term	Definition
Absorption	The process by which digested nutrients pass from the small intestine into the blood present in the blood vessels found in its walls.
Alimentary Canal	The long tube through which food passes, where complex food components are broken down into simpler forms. It starts in the mouth and ends at the anus.
Alveoli	Small, balloon-like sacs in the lungs where the exchange of oxygen and carbon dioxide occurs between the air and the blood.
Bile	A mildly basic secretion from the liver that neutralises acids from the stomach and breaks down fats into tiny droplets.
Breathing	The physical process involving the movement of air into the lungs (inhalation) and out of the lungs (exhalation).
Diaphragm	A dome-shaped muscle located below the lungs that moves downwards during inhalation and upwards during exhalation to change the volume of the chest cavity.
Digestion	The process of breaking down complex food components into simpler forms in the body.
Egestion	The process by which semi-solid waste (stool) is expelled from the body through the anus.
Gills	Specialised structures in most aquatic animals, like fish, that are used for the exchange of gases dissolved in water.
Gizzard	A chamber in the digestive system of birds where food is broken down by the contraction and relaxation of its walls, often with the help of swallowed grit.
Large Intestine	The part of the alimentary canal that is wider and shorter than the small intestine; its function is to absorb water and some salts from undigested food.
Life Processes	Essential processes for the survival of living beings, such as nutrition, circulation, respiration, excretion, and reproduction.
Mechanical Digestion	The initial breakdown of food into fine pieces through physical processes like crushing and chewing by the teeth.
Oesophagus	A long, flexible tube (also called the food pipe) that pushes softened food from the mouth down into the stomach through wave-like motions.
Respiration	The chemical process by which nutrients (like glucose) are converted into usable energy, using oxygen from inhaled air to break them down into carbon dioxide and water.
Ruminants	Grass-eating animals, such as cows and buffaloes, that partially chew food, swallow it, and later bring it back to the mouth for thorough chewing.
Rumination	The process in which partially digested food is brought back from the stomach to the mouth for gradual, thorough chewing.
Small Intestine	The longest part of the alimentary canal (almost 6 meters long) where the final digestion of food occurs and nutrients are absorbed into the blood.
Stool	The semi-solid waste formed in the large intestine from undigested food after water and salts have been absorbed.