Class 10 Science · Chapter 5

Life Processes

431 Class 10 Science questions on Life Processes from the NCERT textbook, NCERT Exemplar and CBSE board papers 2018–2026, each with its answer and a step-by-step solution.

NCERT exercises

Exercises (13) Intext Questions (Page 81) (4) Intext Questions (Page 87) (5) Intext Questions (Page 91) (4) Intext Questions (Page 96) (5) Intext Questions (Page 98) (3)

NCERT Exemplar exercises

Multiple Choice Questions (35) Short Answer Questions (37) Long Answer Questions (10)

CBSE Class 10 Science previous year papers, with answers →

Questions · page 18 of 22

Q341 CBSE 2023

Give two reasons, why bile juice is considered to be an important secretion of liver in the process of digestion ?

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Bile makes the acidic food alkaline for the pancreatic enzymes, and its salts emulsify fats so that lipase acts more efficiently.
(1) The food coming from the stomach is acidic. Bile juice makes it alkaline, so that the pancreatic enzymes, which need an alkaline medium, can act on it. (2) Fats reach the small intestine as large globules, on which enzymes act with difficulty. The bile salts in bile break them into much smaller globules (emulsification), which gives the fat-digesting enzyme lipase a far larger surface to act on and so increases the efficiency of its action. Bile itself contains no digestive enzyme; its importance lies in preparing the food for the pancreatic enzymes.

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Q342 CBSE 2023

What is the other name of ‘tissue fluid’ ? Write its two functions.

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Tissue fluid is also called lymph; it carries absorbed fat from the intestine and drains excess fluid into the blood.
The other name of tissue fluid is lymph. It forms when some plasma, proteins and blood cells escape through the pores in the walls of capillaries into the spaces between the cells. Two functions: (i) Lymph carries digested and absorbed fat from the intestine. (ii) It drains excess fluid from the intercellular (extracellular) spaces back into the blood, through lymph vessels that open into larger veins.

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Q343 CBSE 2023
Write one important function each of the following in the human respiratory system :
1. (a)Rings of Cartilage
2. (b)Alveoli
3. (c)Haemoglobin
4. (d)Lining of mucus
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Cartilage rings keep the windpipe open, alveoli exchange gases, haemoglobin carries oxygen and the mucus lining traps dust and germs.
(a) Rings of cartilage: they ensure that the air passage (the throat or windpipe) does not collapse, so air can pass freely to and from the lungs. (b) Alveoli: they provide a very large, thin surface, richly supplied with blood vessels, where the exchange of gases takes place; oxygen passes into the blood and carbon dioxide passes out of it. (c) Haemoglobin: this respiratory pigment of the red blood corpuscles has a very high affinity for oxygen; it takes up oxygen in the lungs and carries it to the tissues. (d) Lining of mucus: it traps dust particles and germs from the air breathed in, and so helps to filter the air before it reaches the lungs.

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Q344 CBSE 2023

Explain the process of transport of oxygenated and deoxygenated blood in a human body.

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Deoxygenated blood goes from body to right atrium, right ventricle and lungs; oxygenated blood returns to left atrium, left ventricle and body.
Deoxygenated blood from the body organs is brought by the vena cava into the right atrium. The right atrium contracts and passes it to the right ventricle, which pumps it through the pulmonary artery to the lungs. In the lungs the blood gives up carbon dioxide and takes in oxygen, and this oxygenated blood returns through the pulmonary veins to the left atrium. The left atrium contracts and passes it to the left ventricle, whose thick muscular wall pumps it at high pressure into the aorta and so to every organ of the body, where the oxygen is used up and the blood becomes deoxygenated again. The two sides of the heart are separated by a septum and valves prevent any backflow, so the two kinds of blood never mix. Because the blood passes through the heart twice in one complete round, the arrangement is called double circulation.

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Q345 CBSE 2023

What is photosynthesis ? Name the organelle and the organs in which photosynthesis takes place. Where does the oxygen liberated come from during this process ? What happens to the carbohydrates which are not immediately used by the plant ?

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Photosynthesis occurs in chloroplasts of leaves; the oxygen comes from water, and surplus carbohydrate is stored as starch.
Photosynthesis is the process by which green plants prepare their own food: using the energy of sunlight trapped by chlorophyll, they convert carbon dioxide and water into carbohydrate and release oxygen, $6 CO_{2} + 12 H_{2} O \to C_{6} H_{12} O_{6} + 6 O_{2} + 6 H_{2} O$ . The organelle in which it takes place is the chloroplast, and the organs are mainly the leaves, together with other green parts such as green stems. The oxygen liberated comes from **water**: light absorbed by chlorophyll splits water molecules (photolysis) into hydrogen and oxygen, and it is this oxygen that is given out. The carbohydrate that is not used immediately is converted into starch, which is stored in the leaf and, after transport, in storage organs such as roots, tubers, seeds and fruits.

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Q346 CBSE 2023
1. (a)With the help of an activity, explain the action of saliva on the food we eat.
2. (b)Why is bile juice important in the process of digestion ?
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Saliva's amylase breaks starch into maltose, shown by the iodine test; bile makes food alkaline and emulsifies fats.
(a) Activity: take about 1 mL of starch solution in two test tubes A and B; add 1 mL of saliva to A and 1 mL of water to B, and leave both for 20 to 30 minutes. Now add a few drops of dilute iodine solution to each. Tube B turns blue-black, showing starch is still present, while tube A does not, showing the starch has been broken down. Conclusion: the salivary amylase (ptyalin) in saliva acts on starch and converts it into the sugar maltose. (b) Bile juice is important for two reasons: it is alkaline and makes the acidic food coming from the stomach alkaline, so that the pancreatic enzymes can act on it; and the bile salts emulsify fats, breaking large fat globules into small droplets so that lipase has a much larger surface to work on.

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Q347 CBSE 2023
1. (a)Give the structure and function of alveoli in human respiratory system.
2. (b)What is meant by residual volume of air in the lungs ?
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Alveoli are thin-walled, moist, capillary-rich air sacs giving a large surface for gas exchange; residual volume is air that always remains in the lungs.
(a) Structure: the alveoli are balloon-like air sacs at the ends of the finest bronchioles in the lungs. The wall of an alveolus is extremely thin, just one cell thick, and is kept moist, and each alveolus is surrounded by an extensive network of blood capillaries. There are millions of them, giving a total surface of about $80 m^{2}$ in the two lungs. Function: they provide a very large, thin and moist surface for the exchange of gases. Oxygen from the air in the alveoli diffuses into the blood in the capillaries and is carried by haemoglobin, while carbon dioxide brought by the blood diffuses into the alveolar air and is breathed out. (b) Residual volume is the volume of air that always remains in the lungs even after the most forceful expiration (about $1.1$ to $1.2$ litres), because the lungs never empty completely. It ensures that there is sufficient time for oxygen to be absorbed and for carbon dioxide to be released, so gaseous exchange continues between breaths.

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Q348 CBSE 2023

Explain how oxygen is delivered to all parts of the body in human beings. In what form is carbon dioxide transported in our blood ?

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Haemoglobin carries oxygen from the lungs via the heart and arteries to the tissues; carbon dioxide travels mostly dissolved in plasma.
Air breathed in reaches the alveoli of the lungs, whose thin walls are surrounded by a dense network of blood capillaries. Oxygen diffuses from the air in the alveoli into the blood, where it combines with haemoglobin, the respiratory pigment in the red blood cells, which has a very high affinity for oxygen. The oxygen-rich blood is carried by the pulmonary veins to the left atrium, passes into the left ventricle and is pumped through the aorta and the arteries to the capillaries throughout the body. There, where the oxygen concentration is low, oxygen is released from haemoglobin and diffuses into the cells. Carbon dioxide is more soluble in water than oxygen is, so it is mostly transported in the dissolved form, in the plasma of the blood.

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Q349 CBSE 2023
1. (a)Name the glands present in the walls of the stomach and write the secretions which are released by them.
2. (b)Although the liver does not contain any enzyme yet it plays an important role in digestion. Comment.
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Gastric glands release acid, pepsin and mucus; the liver's bile has no enzyme but makes food alkaline and emulsifies fats.
(a) The glands in the wall of the stomach are the gastric glands. They release hydrochloric acid, a protein-digesting enzyme called pepsin, and mucus. The acid makes the medium acidic, which helps pepsin act; pepsin begins the digestion of proteins; mucus protects the inner lining of the stomach from the acid. (b) The liver secretes bile juice, which contains no digestive enzyme, yet it aids digestion in two ways. (1) The food arriving from the stomach is acidic; bile makes it alkaline so that the pancreatic enzymes can act on it. (2) Bile salts break the large fat globules into smaller globules (emulsification), increasing the efficiency of the fat-digesting enzyme lipase.

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Q350 CBSE 2023
1. (i)State the role of ATP in cellular respiration.
2. (ii)What ensures sufficient exchange of gases in plants ?
3. (iii)State the conditions on which the direction of diffusion of gases in plant depend upon.
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ATP is the cell's energy currency; air spaces, stomata and lenticels make gas exchange sufficient; diffusion direction depends on the plant's needs and photosynthesis.
(i) The energy released during cellular respiration is used to make ATP from ADP and inorganic phosphate. ATP is the energy currency of the cell: when the cell needs energy for any process - muscle contraction, protein synthesis, nerve impulse conduction - ATP is broken down into ADP and phosphate and the energy stored in that bond is released to drive the process. (ii) Plants have large intercellular air spaces, so every cell is in contact with air, and they have stomata on the leaves and lenticels on the stems through which gases pass. Because the distance is short and the demand is low, simple diffusion is sufficient. (iii) It depends on the requirement of the plant and on the environmental conditions, mainly whether photosynthesis is going on. At night, when there is no photosynthesis, carbon dioxide diffuses out and oxygen diffuses in. In the day, photosynthesis uses up all the carbon dioxide made in respiration, so carbon dioxide diffuses in and oxygen, which is produced in excess, diffuses out.

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Q351 CBSE 2023
1. (i)What is the first step in the breakdown of glucose during aerobic and anaerobic respiration ? Where does it take place ?
2. (ii)ATP is called the energy currency of the cell. Why ?
3. (iii)What is meant by “residual volume of air” in a breathing cycle ?
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Glycolysis in the cytoplasm is the first step; ATP stores and releases energy for all cell activities; residual air always stays in the lungs.
(i) The first step is **glycolysis**, in which one molecule of glucose (six carbon) is broken down into two molecules of pyruvate (three carbon each). It takes place in the **cytoplasm** of the cell and needs no oxygen, which is why it is common to both aerobic and anaerobic respiration. (ii) The energy released in respiration is stored in ATP, and whenever the cell needs energy for any process, such as muscle contraction, the making of proteins or the conduction of a nerve impulse, the terminal phosphate bond of ATP is broken and that energy is released. Since ATP is the one form in which energy is both stored and spent everywhere in the cell, it is called the energy currency of the cell. (iii) Residual volume is the volume of air that still remains in the lungs even after the most forceful breathing out, and so can never be expelled. It keeps the alveoli from collapsing and gives sufficient time for oxygen to be absorbed and for carbon dioxide to be released.

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Q352 CBSE 2023
(i) How does Paramecium obtain its food ? (ii) List the role of each of the following in our digestive system :
1. (a)Hydrochloric acid
2. (b)Trypsin
3. (c)Muscular walls of stomach
4. (d)Salivary amylase
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Cilia sweep food into Paramecium's food vacuole; HCl lets pepsin act, trypsin digests proteins, stomach muscles churn food and amylase digests starch.
(i) Paramecium is a unicellular organism with holozoic nutrition. Its body is covered with fine hair-like cilia which beat continuously and sweep food particles in the surrounding water towards a fixed oral groove. The food passes into the gullet, a food vacuole forms around it, and enzymes digest the food inside that vacuole; the undigested matter is then thrown out. (ii) (a) Hydrochloric acid makes the medium in the stomach acidic so that the enzyme pepsin can act on proteins, and it kills germs present in the food. (b) Trypsin, an enzyme of the pancreatic juice, digests proteins in the small intestine, breaking them down into smaller peptides, which the intestinal juice then converts into amino acids. (c) The muscular walls of the stomach contract and relax to churn the food and mix it thoroughly with the gastric juice. (d) Salivary amylase in the saliva breaks the starch of the food down into sugar in the mouth.

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Q353 CBSE 2023

List three events that occur during the process of photosynthesis in plants.

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Light is absorbed by chlorophyll, water is split releasing oxygen, and carbon dioxide is reduced to carbohydrates.
Three events that occur during photosynthesis: (i) Absorption of light energy by the chlorophyll present in the chloroplasts of the leaf. (ii) Conversion of the light energy into chemical energy, and splitting of water molecules into hydrogen and oxygen (the oxygen is released into the air). (iii) Reduction of carbon dioxide to carbohydrates, which are stored in the leaf as starch. These three events need not take place one after the other immediately.

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Q354 CBSE 2023
1. (i)What is meant by excretion ?
2. (ii)Name the organ that connects the kidneys with the urinary bladder. State its function.
3. (iii)List two factors on which the amount of water reabsorbed depends.
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Excretion removes harmful metabolic wastes; the ureter carries urine to the bladder; reabsorption depends on excess water and dissolved waste.
(i) Excretion is the biological process by which harmful metabolic wastes, such as the nitrogenous wastes urea and uric acid, are removed from the body. (ii) The ureter (one from each kidney) connects the kidney with the urinary bladder. Its function is to carry the urine formed in the kidney to the urinary bladder, where it is stored until it is passed out through the urethra. (iii) The amount of water reabsorbed depends on (1) how much excess water there is in the body, and (2) how much dissolved waste there is to be excreted.

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Q355 CBSE 2023
1. (i)What is the internal energy reserve in plants and animals ?
2. (ii)How desert plants perform photosynthesis if their stomata remain closed during the day ?
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The energy reserve is starch in plants and glycogen in animals; desert plants fix carbon dioxide at night and photosynthesise by day.
(i) The internal energy reserve in plants is **starch**; in animals (including human beings) it is **glycogen**, stored mainly in the liver and the muscles. (ii) Desert plants take in carbon dioxide at night, when they can open their stomata without losing much water, and fix it at once into an organic acid which is stored in the cell. During the day the stomata remain closed so that no water is lost, and the stored organic acid is broken down to release the carbon dioxide again inside the leaf. This carbon dioxide is then used, together with the sunlight available during the day, to carry out photosynthesis.

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Q356 CBSE 2023

Write in sequence the steps for experimental verification of the fact that “sunlight is essential for photosynthesis”.

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Starch is found, by the iodine test, only in the part of a destarched leaf that received sunlight, showing sunlight is essential.
(1) Keep a healthy potted plant in complete darkness for two to three days, so that the starch already in its leaves is used up (destarching). (2) Cover a part of one leaf on both surfaces with a strip of black paper held by clips. (3) Place the plant in bright sunlight for about six to eight hours. (4) Pluck that leaf and boil it in water for a few minutes to kill the cells. (5) Boil it in alcohol over a water bath until all the green colour is removed, since a water bath is needed because alcohol is inflammable. (6) Wash the decolourised leaf in warm water and pour dilute iodine solution over it. (7) Observation: the uncovered part turns blue-black, showing starch is present, while the covered part stays brown, showing no starch was made there. (8) Conclusion: starch was formed only where sunlight fell, and since every other condition was the same in the two parts of the same leaf, sunlight is essential for photosynthesis.

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Q357 CBSE 2023
1. (i)What is double circulation ?
2. (ii)Why is the separation of the right side and the left side of the heart useful ? How does it help birds and mammals ?
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Blood passes through the heart twice per circuit; separating the two sides prevents mixing, giving birds and mammals the high oxygen supply they need.
(i) Double circulation means that the blood passes through the heart twice during one complete circuit of the body. In the pulmonary circulation, deoxygenated blood goes from the right side of the heart to the lungs and returns, oxygenated, to the left side; in the systemic circulation, that oxygenated blood goes from the left side of the heart to the rest of the body and returns, deoxygenated, to the right side. (ii) The separation of the right and the left sides keeps the deoxygenated and the oxygenated blood from mixing, so the blood sent to the body is fully loaded with oxygen and the supply of oxygen to the tissues is highly efficient. This helps birds and mammals because they are warm-blooded and must keep their body temperature constant, which uses energy all the time; the high and steady oxygen supply is exactly what such a high energy requirement needs.

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Q358 CBSE 2023

What is lymph ? How is lymph different from blood plasma in composition ? List two functions of lymph.

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Lymph is colourless tissue fluid from blood capillaries, with less protein than plasma; it returns absorbed fat and excess fluid to the blood.
Lymph: through the pores in the walls of the blood capillaries, some plasma, proteins and blood cells escape into the spaces between the cells of a tissue. This colourless fluid is lymph (tissue fluid). It is collected by lymph capillaries, passes into larger lymph vessels and is finally emptied into the large veins near the heart. Difference in composition: lymph is similar to blood plasma but contains much less protein; it also carries white blood cells (mainly lymphocytes), whereas plasma is the cell-free fluid part of blood; and lymph is colourless, while plasma is pale yellow. Two functions: (i) it carries digested and absorbed fat from the lacteals of the small intestine into the blood; (ii) it drains the excess fluid from the intercellular spaces back into the blood. (It also helps to fight infection, through the lymph nodes and the lymphocytes it carries.)

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Q359 CBSE 2023
1. (i)In the human respiratory system, name the following : (I) Part where air is filtered by fine hairs and mucus lining (II) Part which separates chest cavity from abdominal cavity (III) Balloon like structures where exchange of gases takes place (IV) The two large air passages that lead from trachea to the lungs
2. (ii)List any two characteristics of lungs which make it an efficient respiratory surface.
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The parts are nasal passage, diaphragm, alveoli and bronchi; lungs have a huge alveolar surface and thin, capillary-rich walls.
(i) (I) The nasal passage, the passage behind the nostrils, which is lined with fine hairs and mucus. (II) The diaphragm. (III) The alveoli. (IV) The bronchi (singular, bronchus). (ii) (1) The lungs contain millions of alveoli, which give a very large surface for the exchange of gases, about 80 square metres if spread out. (2) The walls of the alveoli are very thin and contain an extensive network of blood capillaries, so oxygen and carbon dioxide diffuse quickly between the air and the blood.

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Q360 CBSE 2023

Write any two ways by which plants obtain carbon dioxide. What causes the opening and closing of the stomata ?

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Plants get carbon dioxide through stomata and from water; turgid guard cells open the stomata and flaccid guard cells close them.
Two ways in which plants obtain carbon dioxide: (i) It diffuses in from the air through the stomata, the tiny pores present mainly on the lower surface of the leaves (woody stems take it in through lenticels in the same way); (ii) It is taken in dissolved in water, aquatic plants absorbing the carbon dioxide dissolved in the surrounding water through their general body surface and land plants taking in some along with the water absorbed by the roots. (The carbon dioxide released during the plant's own respiration is also used again, and is an acceptable second answer.) The opening and closing of the stomata is caused by the guard cells: when water flows into the guard cells they swell and become turgid, and because the wall facing the pore is thicker the cells bow apart and the stomatal pore opens; when the guard cells lose water they become flaccid, straighten and come together, and the pore closes.

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