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.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 12 of 22

1. Q221 CBSE 2025
   Where does exchange ​of ​gases occur ​in ​plants ?
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   Gases are exchanged through the stomata of leaves, the lenticels of woody stems and the surface of the roots, by simple diffusion.

   Exchange of gases occurs mainly through the stomata on the surface of the leaves, each pore bounded by two guard cells; through the lenticels in the bark of woody stems; and over the general surface of the roots, including the root hairs, which take up oxygen from the air in the soil. In every case the gases move by simple diffusion.

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2. Q222 CBSE 2025
   State ​the main function ​of ​arteries. ​Why ​do ​they have ​thick and elastic walls ?
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   Arteries carry blood away from the heart to the organs; the blood is under high pressure, so their walls are thick and elastic.

   Main function: arteries carry blood away from the heart to the various organs of the body. Thick and elastic walls: blood emerges from the heart under high pressure, so arteries need thick walls to withstand that pressure, and elastic walls that stretch with each surge of blood pumped by the heart and spring back between beats, keeping the blood moving.

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3. Q223 CBSE 2025
   “In ​human alimentary canal ​the small intestine ​is designed ​to absorb the digested ​food.” ​Justify ​this statement.
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   It completes digestion, is a long coiled tube whose villi enlarge the absorbing surface, and blood vessels carry the food to every cell.

   The small intestine is designed to absorb the digested food because: 1. The digestion of carbohydrates, proteins and fats is completed in it, so the food there is in small soluble molecules (glucose, amino acids, fatty acids and glycerol) that can be absorbed. 2. It is very long and coiled, and its inner lining has numerous finger-like projections called villi, which greatly increase the surface area for absorption. 3. The villi are richly supplied with blood vessels, which take the absorbed food to each and every cell of the body.

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4. Q224 CBSE 2025
   Name the ​tissues ​which form ​the ​vascular bundle. State their ​function ​in plants.
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   Xylem and phloem form the vascular bundle: xylem conducts water and minerals, and phloem conducts food.

   The vascular bundle is formed of the conducting tissues xylem and phloem. Xylem conducts water and the minerals dissolved in it from the roots to the leaves and the other parts of the plant. Phloem conducts the food made in the leaves (the soluble products of photosynthesis), along with amino acids and other substances, to the other parts of the plant, both upwards and downwards; this is called translocation.

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5. Q225 CBSE 2025
   How is ​the ​small intestine ​in humans designed ​to absorb the ​digested food ?
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   It is a long, coiled tube whose villi increase the absorbing surface, and their blood vessels carry the food to every cell.

   The small intestine is designed for absorption in these ways. (1) Its inner lining has numerous finger-like projections called villi, which increase the surface area for absorption. (2) The villi are richly supplied with blood vessels, which take the absorbed food to each and every cell of the body. (3) It is a very long, coiled tube, so the digested food passes over a large area of lining. In each villus a lymph vessel, the lacteal, also takes up absorbed fat.

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6. Q226 CBSE 2025
   Besides minimising the ​loss of ​blood, why is it ​essential ​to plug any leak in a blood ​vessel? Name the component of blood which ​helps in this process ​and state how this component perform this function.
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   Plugging a leak keeps the pressure of the circulation; platelets stick at the cut and start clotting, and fibrin threads seal it.

   The blood inside our vessels is under pressure, and it is that pressure which drives blood to every tissue. If a leak is not plugged, the pressure in the system falls and the pumping of blood by the heart is no longer efficient, so the organs stop receiving enough blood. Plugging the leak therefore preserves the pressure of the circulation, not just its volume. The component of blood responsible is the platelet cell (thrombocyte). Platelets circulate all over the body. When a vessel is injured they reach the site, stick to the cut edges and pile up to form a temporary plug, and they set off the clotting process in which soluble fibrinogen of the plasma is converted into insoluble threads of fibrin. The fibrin mesh traps blood cells and forms a clot that seals the leak.

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7. Q227 CBSE 2025
   How is lymph formed ? ​State ​its important ​function.
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   Plasma and proteins leak from capillaries into tissue spaces as lymph, which carries absorbed fat and drains excess fluid back into the blood.

   Lymph is formed when some plasma, along with some proteins and blood cells, escapes through the pores in the walls of the blood capillaries into the spaces between the cells of a tissue. This fluid, called lymph or tissue fluid, is similar to plasma but is colourless and contains less protein. Its important functions are that it carries digested and absorbed fat from the intestine, through the lacteals of the villi, and that it drains the excess fluid from the extracellular space back into the blood.

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8. Q228 CBSE 2025
   1. (i)The ​transport system ​in ​plants is ​relatively slower than in animals. ​Give reasons.
   2. (ii)State the role of phloem in ​the transport ​of materials in plants.
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   Plants have no pump and low energy needs, so transport is slow; phloem translocates sugars from leaves to other parts, upwards and downwards.

   (i) Plants have no pump. An animal's heart drives blood round a closed circuit under high pressure, whereas in a plant water rises only because evaporation from the leaves creates a transpiration pull, and food moves only because of osmotic pressure differences set up in the phloem; neither is driven by an organ. In addition, plants do not move about, so their energy needs are low, and a large part of a plant body is made of dead cells (xylem, wood and bark) which need nothing at all. A slow transport system is therefore sufficient for a plant. (ii) Phloem carries the products of photosynthesis - mainly soluble sugars such as sucrose, together with amino acids and other substances - from the leaves, where they are made, to the roots, growing buds, fruits and seeds where they are used or stored. This transport, called translocation, is an active process: material is loaded into the sieve tubes using energy from ATP, water then enters by osmosis and the resulting pressure moves the material to tissues at lower pressure. Because of this, phloem can carry material both upwards and downwards, unlike the xylem.

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9. Q229 CBSE 2025
   1. (a)Identify 'X' ​in the figure of human ​nephron shown below. ​What role does it play in ​the process of urine formation ?
   2. (b)Why some substances are selectively reabsorbed from the initial filtrate ​of urine, as it flows along ​the tabular part of nephron ​?

   Show answer

   X is the Bowman's capsule, which collects the initial filtrate; useful substances are reabsorbed selectively because the body still needs them.

   (a) X is the Bowman's capsule. It is the cup-shaped, double-walled structure at the beginning of the nephron that surrounds the glomerulus. Blood is filtered under pressure in the glomerulus, and the Bowman's capsule collects this initial filtrate - water, glucose, amino acids, salts and urea - and passes it on into the tubular part of the nephron. (b) Filtration separates by size, so the initial filtrate contains useful substances as well as waste. As it flows along the tubular part, glucose, amino acids, most salts and most water are selectively reabsorbed into the blood because the body still needs them and losing them would waste food and water; urea and the excess salts and water are left behind, and what remains is urine.

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10. Q230 CBSE 2025
    Explain ​how circulation of ​blood takes ​place ​in ​fishes.
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    Blood passes once through the fish's two-chambered heart, going to the gills and then the body: single circulation.

    A fish has a two-chambered heart (one atrium and one ventricle). The heart receives deoxygenated blood from the body and pumps it to the gills, where it takes up oxygen from the water and becomes oxygenated. The oxygenated blood flows directly to the rest of the body and, after giving up its oxygen, returns deoxygenated to the heart. Blood passes through the heart only once in each round, so this is called single circulation.

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11. Q231 CBSE 2025
    Write ​the role ​of the following ​in the ​process ​of digestion in human beings ​:

    1. (i)Salivary ​amylase
    2. (ii)Hydrochloric acid
    3. (iii)Trypsin
    4. (iv)Intestinal ​villi
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    Salivary amylase starts starch digestion, HCl provides an acidic medium for pepsin, trypsin digests proteins and villi increase absorption.

    (i) Salivary amylase, the enzyme of saliva, begins digestion in the mouth by breaking starch into the sugar maltose. (ii) 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. (iii) Trypsin, an enzyme of the pancreatic juice, digests proteins into amino acids in the small intestine. (iv) Intestinal villi are finger-like projections that increase the surface area for absorption and pass the absorbed food into the blood vessels inside them.

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12. Q232 CBSE 2025
    How does ​blood ​come ​back to ​the heart ​from ​different ​parts of the body ?
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    Blood from the organs flows through capillaries, venules and veins, whose valves prevent backflow, into the venae cavae and the right atrium.

    Blood leaving the organs is collected by capillaries, which join into venules and then into veins. Veins are thin-walled vessels carrying blood at low pressure, and they have valves that open only towards the heart, so the blood cannot flow backwards; the squeezing of the surrounding muscles helps drive it on. The veins of the body unite into the superior and inferior venae cavae, which empty the deoxygenated blood into the right atrium, while the pulmonary veins bring oxygenated blood from the lungs into the left atrium.

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13. Q233 CBSE 2025
    On the basis of ​the characteristics of ​the processes given in ​the brackets in each ​case, differentiate between the following :

    1. (a)Products ​of breakdown of pyruvate in aerobic and anaerobic respiration ​in human beings (product(s) of the processes)
    2. (b)Respiration and photosynthesis in plants (gas released)
    3. (c)Respiration in terrestrial ​animals and fishes (organs involved)
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    Aerobic respiration gives ${\text{CO}}_2$ and water but anaerobic gives lactic acid; respiration releases ${\text{CO}}_2$, photosynthesis ${\text{O}}_2$; terrestrial animals use lungs, fishes gills.

    (a) In aerobic respiration pyruvate is broken down completely in the mitochondria, in the presence of oxygen, into carbon dioxide and water; in anaerobic respiration in human muscle, when oxygen is lacking, pyruvate is converted into lactic acid. (b) Respiration releases carbon dioxide; photosynthesis releases oxygen. (c) Terrestrial animals respire through lungs, taking oxygen from the air; fishes respire through gills, taking oxygen dissolved in the water.

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14. Q234 CBSE 2025
    1. (a)Write the ​end products of ​the breakdown ​of pyruvate ​in yeast cells and in ​our muscle cells under anaerobic conditions.
    2. (b)In which part of ​the ​cell does the above process take place ?
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    Yeast gives ethanol and carbon dioxide; muscle cells give lactic acid; both processes take place in the cytoplasm.

    (a) In yeast cells the breakdown of pyruvate under anaerobic conditions gives ethanol, that is ethyl alcohol, and carbon dioxide, together with energy; this is fermentation. In our muscle cells the breakdown of pyruvate when the oxygen supply is short gives lactic acid and energy. (b) In both cases the process takes place in the cytoplasm of the cell. Only the breakdown of pyruvate in the presence of oxygen, which gives carbon dioxide and water, takes place in the mitochondria.

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15. Q235 CBSE 2025
    The digestion of food in human alimentary canal is a complex process. ​State the ​enzyme/salt ​present in the following and mention their function ​in the process of ​digestion :

    1. (i)Saliva
    2. (ii)​Bile Juice
    3. (iii)​Pancreatic Juice
    Show answer

    Saliva has salivary amylase (starch to maltose); bile has salts that make food alkaline and emulsify fats; pancreatic juice has trypsin and lipase.

    (i) Saliva contains the enzyme salivary amylase (ptyalin), which breaks down starch into maltose, a simpler sugar. (ii) Bile juice contains bile salts and no enzyme; they make the acidic food coming from the stomach alkaline so that pancreatic enzymes can act, and they emulsify fats by breaking large fat globules into small droplets. (iii) Pancreatic juice contains trypsin, which digests proteins into amino acids, and pancreatic lipase, which breaks down emulsified fats into fatty acids and glycerol.

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16. Q236 CBSE 2025
    1. (a)Write the name and one function of respiratory pigment found ​in human beings.
    2. (b)Why do lungs always ​contain a ​residual ​volume ​of air ?
    3. (c)Why ​is ATP known as ​energy currency of the living beings ?
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    Haemoglobin carries oxygen; residual air keeps alveoli open and allows time for exchange; ATP stores and releases energy for all cell activities.

    (a) The respiratory pigment is haemoglobin, present in the red blood cells. It has a very high affinity for oxygen: it binds oxygen in the alveoli of the lungs and carries it to all the tissues of the body, where it releases it. (b) We never breathe out completely, so a residual volume of air always stays in the lungs. It keeps the alveoli inflated so that they do not collapse, and it keeps air in contact with the exchange surface, giving sufficient time for oxygen to be absorbed and carbon dioxide to be released even between two breaths. (c) The energy released in cellular respiration is used to make ATP from ADP and inorganic phosphate, and whenever a cell needs energy — for muscle contraction, protein synthesis or nerve impulse conduction — the terminal phosphate bond of ATP is broken and that energy is released. Since energy is stored and spent in this one molecule throughout the body, ATP is called the energy currency of living beings.

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17. Q237 CBSE 2025
    Name the blood vessel that brings ​

    1. (i)oxygenated blood
    2. (ii)​deoxygenated ​blood, to the human heart. ​Also name that chamber ​of the heart which receives deoxygenated blood and state how deoxygenated blood ​from this chamber ​is sent to lungs for oxygenation.
    Show answer

    Pulmonary vein brings oxygenated blood; vena cava brings deoxygenated blood to the right atrium, then right ventricle, pulmonary artery and lungs.

    (i) The pulmonary vein brings oxygenated blood to the heart, from the lungs into the left atrium. (ii) The vena cava, that is the superior and inferior venae cavae, brings deoxygenated blood from the body to the heart. The chamber that receives this deoxygenated blood is the right atrium (right auricle). From it the blood passes through the tricuspid valve into the right ventricle, and the right ventricle contracts and pumps the blood through the pulmonary artery to the lungs, where it is oxygenated.

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18. Q238 CBSE 2025
    1. (a)Enlist any ​two nitrogenous ​waste products removed ​from ​the ​blood of human kidney.
    2. (b)Name the capillary cluster formed by the branch of renal artery ​in the Bowman’s capsule.
    3. (c)Depict in ​the form of a flow chart ​the path of the urine formed in each kidney until it is finally passed out through the urethra.
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    Urea and uric acid; the glomerulus; and urine flows from the kidney through the ureter, urinary bladder and urethra to the outside.

    (a) Urea and uric acid. (b) Glomerulus. (c) Kidney (urine formed in the nephrons) → Ureter → Urinary bladder (urine stored) → Urethra → passed out of the body.

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19. Q239 CBSE 2025
    Why ​is ​blood circulation in vertebrates known as “double ​circulation”? ​Trace its path ​in the ​form of a ​flow chart.
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    Blood passes twice through the heart in one cycle: through the right side to the lungs, and through the left side to the body.

    In one complete cycle round the body the blood passes through the heart twice — once through the right side on its way to the lungs (pulmonary circulation) and once through the left side on its way to the body (systemic circulation) — so the circulation is called double circulation. (This is the pattern in the vertebrates other than fishes; in fishes the blood passes through the heart only once per cycle.) Flow chart: body organs → vena cava → right atrium → right ventricle → pulmonary artery → lungs (blood is oxygenated) → pulmonary veins → left atrium → left ventricle → aorta → body organs (oxygen is given up) → vena cava → right atrium.

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20. Q240 CBSE 2025
    1. (i)Study ​the diagram and ​name the parts marked as A, ​B, C and ​D.
    2. (ii)​Write ​the function of A and ​C.

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    A pulmonary artery, B pulmonary vein, C aorta, D vena cava; A carries blood to the lungs and C to the body.

    (i) A – pulmonary artery; B – pulmonary vein; C – aorta; D – vena cava. (ii) A, the pulmonary artery, carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation. C, the aorta, carries oxygenated blood from the left ventricle to all parts of the body.

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