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 9 of 22

1. Q161 CBSE 2026
   How ​does ​translocation ​of food and other substances take place in ​plants ​?
   Show answer

   Phloem loads food into sieve tubes using ATP; water enters by osmosis and the pressure pushes it to sinks, upwards or downwards.

   Translocation is the transport of food - the soluble products of photosynthesis - and of other substances such as amino acids, and it is carried out by the phloem, whose sieve tubes and companion cells run through the plant. At a source such as a leaf, the food is loaded into the sieve tubes using energy from ATP; this raises the concentration inside the tube, so water enters it by osmosis and the pressure inside rises. The pressure pushes the contents along the sieve tubes to a sink - a root, a fruit or a growing bud - where the food is unloaded and the pressure falls. Because the pressure is created wherever food is loaded, the phloem can carry material both upwards and downwards, according to the needs of the plant.

   Step-by-step solution →
2. Q162 CBSE 2026
   Transport of ​water and minerals in plants takes place through xylem tissue where vessels and tracheids of roots, stems and leaves are interconnected. ​This forms a continuous system of channels reaching all plant parts. Simple physical forces ​are involved ​in the ​process. If the soil has adequate water, name and explain which force will ​be acting effectively ​at :

   1. (i)Night
   2. (ii)​Day
   Show answer

   At night root pressure acts, with stomata closed; during the day transpiration pull acts, with stomata open.

   (i) Night — root pressure. With the stomata closed there is almost no evaporation from the leaves, so no suction is produced above. Meanwhile the root cells go on actively taking up ions from the soil and passing them into the xylem; this raises the concentration inside the root above that of the soil water, water enters the root by osmosis, and its continuous entry at the base pushes the column of water up the xylem. That push is root pressure. (ii) Day — transpiration pull. The stomata are open, water evaporates from the leaf cells and diffuses out, and each molecule lost is replaced from the xylem. This creates a suction at the top of the water column, and because the vessels and tracheids form one continuous channel holding an unbroken thread of water, the suction is transmitted all the way down and pulls water up from the roots. Transpiration pull is by far the stronger of the two and is the main force during the day.

   Step-by-step solution →
3. Q163 CBSE 2026
   Explain mechanism ​of ​opening ​and ​closing of stomata ​in plants.
   Show answer

   Water entering the guard cells makes them turgid and the pore opens; water leaving makes them flaccid and the pore closes.

   A stoma is a tiny pore in the leaf epidermis bordered by a pair of bean-shaped guard cells, and the opening and closing of the pore is a function of these cells. When water flows into the guard cells by osmosis they swell and become turgid; because the wall facing the pore is thick and stiff while the outer wall is thin and elastic, each cell curves outwards, its inner wall is drawn away from its partner and the pore opens. When water passes out of the guard cells they shrink and become flaccid, straighten and come together again, so the pore closes. This closing is what saves the plant from losing water through the stomata when carbon dioxide is not needed.

   Step-by-step solution →
4. Q164 CBSE 2026
   Although ​plants do not ​have excretory ​system still they ​are able to ​get ​rid-off their ​waste products. ​How ?
   Show answer

   Plants release gaseous wastes by diffusion, lose excess water by transpiration, store wastes, shed them in leaves, or release them into the soil.

   Plants do not need an excretory organ because every kind of waste they make already has a way out of the body, and their slow rate of metabolism means the waste is never produced faster than these routes can clear it. (i) Gaseous wastes leave by diffusion. Oxygen made in photosynthesis and carbon dioxide made in respiration pass out through the stomata of the leaves and the lenticels of the stem, and excess water is lost as water vapour through the stomata during transpiration. (ii) Wastes that cannot diffuse out are stored where they do no harm. Many are kept in the vacuoles of the cells, and others are laid down as resins and gums, chiefly in the old xylem, which is dead tissue. (iii) Some wastes are moved into leaves, and the leaves are then shed, so the waste goes with them. (iv) Some waste substances are released into the soil around the roots.

   Step-by-step solution →
5. Q165 CBSE 2026
   The leaves of a plant first prepares food 'P' ​by ​photo-synthesis. Food 'P' ​is then converted to food 'Q', which is ​stored in the leaves if not used immediately. What are 'P' and 'Q' ? ​What are the raw materials ​and conditions ​required for synthesis of 'P' ?
   Show answer

   P is glucose and Q is starch; photosynthesis needs carbon dioxide and water as raw materials, and sunlight and chlorophyll as conditions.

   'P' is glucose, a simple carbohydrate of formula ${\text{C}}_6{\text{H}}_{12}{\text{O}}_6$. It is the first food the leaf prepares by photosynthesis. 'Q' is starch. The glucose the plant does not use immediately is converted into starch, which is insoluble and is stored in the leaves as the plant's internal energy reserve, to be broken back down to glucose when it is needed. The raw materials required for the synthesis of 'P' are carbon dioxide, taken from the air through the stomata of the leaf, and water, absorbed from the soil by the roots and carried up in the xylem. The conditions required are sunlight, which supplies the energy, and chlorophyll, the green pigment in the chloroplasts that absorbs the light energy and converts it into chemical energy. In symbols: $6{\text{CO}}_2+6{\text{H}}_2\text{O}\underset{\text{chlorophyll}}{\overset{\text{sunlight}}{\to }}{\text{C}}_6{\text{H}}_{12}{\text{O}}_6+6{\text{O}}_2$.

   Step-by-step solution →
6. Q166 CBSE 2026
   What kind ​of respiration ​provides ​more ​energy and why ​?
   Show answer

   Aerobic respiration gives more energy because it breaks glucose down completely with oxygen, whereas anaerobic respiration breaks it down only partially.

   Aerobic respiration provides more energy. In aerobic respiration glucose is broken down completely, in the presence of oxygen in the mitochondria, into carbon dioxide and water, so all the energy respiration can obtain from it is released (up to about 38 ATP per glucose molecule). In anaerobic respiration, without oxygen, glucose is broken down only partially, into ethanol and carbon dioxide in yeast or lactic acid in muscle cells, so much of its energy stays locked in these products and only 2 ATP are formed.

   Step-by-step solution →
7. Q167 CBSE 2026
   Why the lungs ​always ​contain ​a residual ​volume of air ​?
   Show answer

   Residual air keeps gas exchange going between breaths, giving sufficient time for oxygen to be absorbed and carbon dioxide released.

   The lungs never empty completely so that gaseous exchange never has to stop. Breathing is rhythmic, so fresh air reaches the alveoli only when we breathe in, but blood flows through the capillaries around the alveoli all the time. Because a residual volume of air always stays in the alveoli, oxygen keeps diffusing from this air into the blood and carbon dioxide keeps diffusing from the blood into it, even while we are breathing out and between one breath and the next. There is therefore sufficient time for oxygen to be absorbed and for carbon dioxide to be released. The air left behind also keeps the alveoli inflated, so the large exchange surface stays open instead of collapsing at the end of every expiration.

   Step-by-step solution →
8. Q168 CBSE 2026
   Separation of right side ​and left side ​of the heart ​is useful to keep oxygenated and deoxygenated ​blood from mixing. Various organisms have different types of heart. (I) Fill in the blanks (i) to (iii) correctly according to the type of organisms and their evolution in terms of blood ​circulation : (II) Which type of circulation is ​most efficient ?

   Organisms	Number of chambers in heart	Type of blood being circulated	Type of circulation
   Fish	(i) ______	Mixed	Single
   (ii) ______	3-chambered	Mixed	Incomplete double circulation
   Birds and Mammals	4-chambered	Separated circulation path of oxygenated and deoxygenated blood	(iii) ______

   Show answer

   The blanks are 2-chambered, amphibians and reptiles, and double circulation, which is also the most efficient as it keeps oxygenated and deoxygenated blood apart.

   (I) (i) 2-chambered (one atrium and one ventricle); (ii) Amphibians and reptiles, e.g. frog and lizard; (iii) Double circulation (complete double circulation). (II) Double circulation, as in birds and mammals, is the most efficient: the fully separated right and left sides of the 4-chambered heart keep oxygenated and deoxygenated blood from mixing, so the body gets a highly efficient supply of oxygen.

   Step-by-step solution →
9. Q169 CBSE 2026
   Briefly ​mention ​the ​steps ​in ​double-circulation ​through ​human heart.
   Show answer

   Blood passes twice through the heart: body to right atrium, right ventricle, lungs, left atrium, left ventricle and back to the body.

   Double circulation means that blood passes through the heart twice in one complete round of the body: (1) Deoxygenated blood from the body enters the right atrium through the vena cava; the right atrium contracts and passes it to the right ventricle. (2) The right ventricle pumps it through the pulmonary artery to the lungs, where it gives up ${\text{CO}}_2$ and takes up ${\text{O}}_2$. (3) The oxygenated blood returns through the pulmonary veins to the left atrium, which contracts and passes it to the left ventricle. (4) The left ventricle pumps it through the aorta to all parts of the body; there it gives up oxygen and returns to the right atrium, and the cycle repeats. Steps (2) and (3) form the pulmonary circulation (heart to lungs to heart) and steps (4) and (1) the systemic circulation (heart to body to heart). Valves stop the blood from flowing backwards.

   Step-by-step solution →
10. Q170 CBSE 2026
    Given below is a diagrammatic representation of cross-section ​of a leaf :

    1. (i)​Identify 'P' in ​the given ​diagram and write down its ​role in plants.
    2. (ii)Write down a balanced equation ​of ​process of photo-synthesis.

    Show answer

    P is a chloroplast, where chlorophyll absorbs sunlight and the plant prepares its food by photosynthesis.

    (i) P is a chloroplast, present in a palisade mesophyll cell of the leaf. It contains the green pigment chlorophyll, which absorbs the sunlight falling on the leaf, and it is the site of photosynthesis: inside it the absorbed light energy is converted into chemical energy, water is split and the oxygen released, and carbon dioxide is reduced to carbohydrate, so the chloroplast is where the plant prepares its own food. (ii) $6{\text{CO}}_2+12{\text{H}}_2\text{O}\underset{\text{Chlorophyll}}{\overset{\text{Sunlight}}{\to }}{\text{C}}_6{\text{H}}_{12}{\text{O}}_6+6{\text{O}}_2+6{\text{H}}_2\text{O}$

    Step-by-step solution →
11. Q171 CBSE 2026
    In the human ​digestive ​system, food is digested with the help ​of certain ​enzymes like trypsin and ​secretions from various glands like bile juice. Name the ​gland that secretes them and ​explain their action on food.
    Show answer

    The pancreas secretes trypsin, which digests proteins; the liver secretes bile juice, which makes food alkaline and emulsifies fats.

    Trypsin is secreted by the pancreas and bile juice by the liver (the bile is stored in the gall bladder and released into the small intestine). Action on food: bile juice carries no enzyme; it makes the acidic food coming from the stomach alkaline so that the pancreatic enzymes can act, and its bile salts emulsify fats by breaking large fat globules into small droplets, which increases the surface for enzyme action. Trypsin, poured in with the pancreatic juice, acts on this alkaline food and digests proteins, breaking them into smaller molecules that are absorbed as amino acids.

    Step-by-step solution →
12. Q172 CBSE 2026
    Complete ​the ​pathways given below, showing the ​breakdown ​of glucose. Identify 'A', ​'B', 'C', ​'D', 'E' ​and 'F'.

    Show answer

    A is cytoplasm, B ethanol, C carbon dioxide, D lactic acid, E carbon dioxide and F water.

    'A': Cytoplasm (glucose is broken down to pyruvate in the cytoplasm; this step is glycolysis) 'B': Ethanol 'C': Carbon dioxide 'D': Lactic acid 'E': Carbon dioxide 'F': Water

    Step-by-step solution →
13. Q173 CBSE 2026
    Observe the ​following diagrams :

    1. (a)​What change will be observed ​in ​Cases ​‘P’, ‘Q’ ​and ‘R’ ? Give reasons.
    2. (b)In which case : (i) is aerobic ​respiration taking ​place ? (ii) is fermentation taking place ?

    Show answer

    Lime water turns milky very slowly in P, quickly in Q, and also in R; aerobic respiration is in Q, fermentation in R.

    (a) Case P: The lime water turns milky only very slowly; it stays clear for a long time, because the air pumped through it contains very little carbon dioxide (about $0.04\%$). Case Q: The lime water turns milky quickly, because breathed-out air contains much more carbon dioxide (about $4\%$), produced by respiration in the body's cells. Case R: The lime water turns milky, because the yeast ferments the sugar into ethanol and carbon dioxide, and the carbon dioxide passes through the delivery tube into the lime water. In each case carbon dioxide turns lime water milky by forming insoluble white calcium carbonate: ${\text{Ca(OH)}}_2+{\text{CO}}_2\to {\text{CaCO}}_3+{\text{H}}_2\text{O}$. (b) (i) Aerobic respiration: Case Q. (ii) Fermentation: Case R.

    Step-by-step solution →
14. Q174 CBSE 2026
    1. (a)Draw a ​neat diagram of the human respiratory ​system and ​label its lungs, ​trachea, ​bronchi and alveoli.
    2. (b)State the roles of the following ​in the process of respiration : (i) ​Alveoli (ii) Respiratory pigments
    Show answer

    Alveoli are the site of gas exchange, and haemoglobin carries oxygen from the lungs to the tissues.

    (a) See the labelled diagram: the trachea, held open by rings of cartilage, divides into two bronchi, one entering each lung; inside the lungs the bronchi branch into bronchioles, which end in clusters of alveoli. The lungs lie in the chest cavity above the diaphragm. (b) (i) Alveoli: They are the site of exchange of gases. Oxygen from the air in the alveoli diffuses into the blood in the surrounding capillaries, and carbon dioxide diffuses from the blood into the alveoli to be breathed out. Their very large number gives a very large surface for this exchange. (ii) Respiratory pigments: Haemoglobin, present in the red blood cells, has a very high affinity for oxygen. It takes up oxygen from the air in the lungs and carries it to the tissues that are short of oxygen, where it releases it.

    Step-by-step solution →
15. Q175 CBSE 2026
    In xylem tissue, vessels and tracheids of ​the roots, ​stems and leaves are interconnected ​to form a continuous system of water-conducting channels reaching all parts of the plant. ​Explain ​how ​this is ​achieved.
    Show answer

    Vessels and tracheids joined end to end form a continuous column of water, moved up by root pressure and transpiration pull.

    The tracheids and vessels of the root, stem and leaf are joined end to end, so the water in them forms one continuous column, and two forces move it: (1) Root pressure: root cells in contact with the soil actively take up ions, so the ion concentration in the root becomes higher than in the soil; water moves from the soil into the root to remove this difference, and this steady entry of water into the root xylem pushes the water column upwards. (2) Transpiration pull: water evaporates from the leaf cells through the stomata; the water lost is replaced from the xylem vessels in the leaf, which creates a suction that pulls water up from the xylem of the roots. (3) Root pressure is more important at night; during the day, when the stomata are open, transpiration pull is the major driving force.

    Step-by-step solution →
16. Q176 CBSE 2026
    During respiration, ​glucose is broken down into pyruvate. ​State the ​end products formed from it on ​further breakdown, in each of ​the following cases ​:

    1. (a)In yeast, in ​absence of oxygen.
    2. (b)Lack ​of oxygen in muscles.
    3. (c)In presence of oxygen in mitochondria.
    Show answer

    Yeast gives ethanol and carbon dioxide, muscles give lactic acid, and mitochondria with oxygen give carbon dioxide and water.

    (a) In yeast, in the absence of oxygen: ethanol (ethyl alcohol) and carbon dioxide, with a small amount of energy released. This is fermentation. (b) In muscles lacking oxygen: lactic acid, with a small amount of energy released. (c) In the presence of oxygen in the mitochondria: carbon dioxide and water, with a much larger amount of energy released. This is aerobic respiration.

    Step-by-step solution →
17. Q177 CBSE 2026
    Give reasons for the ​following :

    1. (a)​Plants do not have an excretory system so ​how they excrete their wastes ?
    2. (b)​Why do ​mammals and ​birds ​have double circulation ?
    Show answer

    Plants excrete through stomata, lenticels, transpiration and by storing or shedding wastes; warm-blooded mammals and birds need a highly efficient oxygen supply.

    (a) A plant has no excretory organ, so each waste leaves by the route that suits it. Gaseous wastes - the oxygen made in photosynthesis and the carbon dioxide made in respiration - diffuse out through the stomata of the leaves and the lenticels of the stem. Excess water is lost as water vapour by transpiration. Other wastes are stored in the vacuoles of cells, deposited as resins and gums in old xylem, which is already dead tissue, or moved into leaves and bark that are then shed; some are passed out into the soil around the roots. (b) Because they are warm-blooded. A mammal or a bird holds its body temperature constant whatever the surroundings do, and it can only do that by oxidising food continuously, so its demand for energy - and therefore for oxygen - is high and constant. Double circulation, with a completely four-chambered heart, keeps the oxygenated and the deoxygenated blood from mixing, so the blood delivered to the tissues carries its full load of oxygen; and because the blood returns to the heart after the lungs, it is pumped out to the body a second time at high pressure. Together these give the efficient, high-rate oxygen supply that a warm-blooded body needs.

    Step-by-step solution →
18. Q178 CBSE 2026
    Give reasons for the following :

    1. (a)Herbivores have a longer small intestine.
    2. (b)Inner lining of small ​intestine has numerous finger-like projections.
    3. (c)​Rate of breathing in ​aquatic ​organisms is much faster than ​that in ​terrestrial organisms.
    Show answer

    Herbivores need time to digest cellulose; villi increase absorbing surface; water holds less oxygen than air, so aquatic organisms breathe faster.

    (a) Herbivores eat plant food rich in cellulose, which takes a long time to digest; a longer small intestine holds the food for longer and gives the cellulose the time it needs to be digested. (b) The finger-like projections are villi. They increase the surface area for the absorption of digested food, and they are richly supplied with blood vessels that carry the absorbed food to all parts of the body. (c) Water holds far less dissolved oxygen than the same volume of air, so aquatic organisms must pass much more water over their gills, and therefore breathe much faster, to obtain the oxygen they need.

    Step-by-step solution →
19. Q179 CBSE 2026
    1. (a)List any two factors ​on which the amount of water ​reabsorbed ​from the filtrate depends in the human ​kidneys.
    2. (b)Write any two methods used ​by plants ​to get rid of excretory ​products.
    Show answer

    Water reabsorption depends on excess body water and dissolved waste; plants store wastes in vacuoles and as resins and gums in old xylem.

    (a) The amount of water reabsorbed from the filtrate depends on (i) the amount of excess water in the body at that time, and (ii) the amount of dissolved waste that has to be excreted, since the wastes can only be carried out dissolved in water. (b) (i) Many plant waste products are stored in the vacuoles of cells; (ii) Other waste products are stored as resins and gums in the old xylem. (Wastes are also stored in leaves that later fall off and in dead tissues; in addition, plants lose excess water by transpiration and release some wastes into the soil around them.)

    Step-by-step solution →
20. Q180 CBSE 2026
    Name the organ that helps ​in the digestion ​of ​fats in human ​beings. ​Also describe its complete digestion into ​simple form. Where does ​absorption ​of food take place in the humans ?
    Show answer

    The liver's bile emulsifies fats, lipase then converts them to fatty acids and glycerol, and absorption takes place in the small intestine.

    Organ: the **liver**, which secretes bile juice (stored in the gall bladder and released into the small intestine). The pancreas, which secretes lipase, and the small intestine, where fat digestion is completed, also help in the digestion of fats. Complete digestion of fat: fats reach the small intestine as large globules. The bile salts of the bile juice break these large globules into many small droplets — emulsification — which greatly increases the surface available to the enzyme. The enzyme lipase, present in the pancreatic juice secreted by the pancreas and in the intestinal juice, then acts on this emulsified fat and breaks it down completely into its simple form, **fatty acids** and **glycerol**. Absorption: absorption of the digested food takes place in the **small intestine**, through the finger-like projections called villi in its inner lining, which give a large absorbing surface and are richly supplied with blood vessels that carry the absorbed food to every cell of the body.

    Step-by-step solution →