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 13 of 22

1. Q241 CBSE 2025
   What is the first step ​of cellular respiration? In which part ​of the cell does it occur ? Write the equation for ​the process of breakdown of glucose ​in a ​human cell :

   1. (i)in the presence of ​oxygen
   2. (ii)due to lack of oxygen
   Show answer

   The first step is glycolysis in the cytoplasm; glucose then gives carbon dioxide and water with oxygen, or lactic acid when oxygen is lacking.

   The first step of cellular respiration is glycolysis: glucose, a six-carbon molecule, is broken down into pyruvate, a three-carbon molecule, with the release of some energy. It occurs in the cytoplasm. (i) In the presence of oxygen, pyruvate is broken down in the mitochondria: $\text{Glucose}\stackrel{\text{cytoplasm}}{\to }\text{Pyruvate}+\text{energy}\stackrel{\text{oxygen, mitochondria}}{\to }{\text{CO}}_2+{\text{H}}_2\text{O}+\text{energy}$; overall, ${\text{C}}_6{\text{H}}_{12}{\text{O}}_6+6{\text{O}}_2\to 6{\text{CO}}_2+6{\text{H}}_2\text{O}+\text{energy}$. (ii) Due to lack of oxygen, in our muscle cells: $\text{Glucose}\stackrel{\text{cytoplasm}}{\to }\text{Pyruvate}+\text{energy}\stackrel{\text{lack of oxygen}}{\to }\text{Lactic acid}+\text{energy}$; overall, ${\text{C}}_6{\text{H}}_{12}{\text{O}}_6\to 2{\text{C}}_3{\text{H}}_6{\text{O}}_3+\text{energy}$.

   Step-by-step solution →
2. Q242 CBSE 2025
   1. (i)Name the ​movement that ​occurs all along the gut in the human digestive system. ​How do ​these ​movements help in ​the digestion of food ?
   2. (ii)Where is bile juice stored in the human body ? ​List its two roles.
   Show answer

   Peristalsis pushes food along and mixes it with digestive juices; bile is stored in the gall bladder and neutralises acid and emulsifies fats.

   (i) The movement is **peristalsis** (peristaltic movement) — rhythmic waves of contraction and relaxation of the smooth muscles in the wall of the alimentary canal, which occur all along the gut. It helps digestion in two ways: it pushes the food steadily forward through the whole canal so that each region gets the food for the right time, and it churns the food and mixes it thoroughly with the digestive juices, so that the enzymes act on every part of it and the digested food is brought into contact with the absorbing surface. (ii) Bile juice is made in the liver but is **stored in the gall bladder**. Its two roles are: (1) it is alkaline, so it neutralises the acidic food coming from the stomach and makes the medium alkaline, which the pancreatic enzymes need in order to act; and (2) its bile salts **emulsify** fats — they break large fat globules into many small globules, greatly increasing the surface area so that the enzyme lipase can digest the fat efficiently.

   Step-by-step solution →
3. Q243 CBSE 2025
   Give reason for each ​of ​the ​following :

   1. (i)Alveoli in lungs are richly supplied with blood capillaries.
   2. (ii)Respiratory pigment in the ​blood takes up ​oxygen and not carbon dioxide ​gas.
   3. (iii)During anaerobic respiration, a 3-carbon molecule is formed as an ​end product instead of ${\text{CO}}_2$ in ​human beings.
   Show answer

   Alveoli need dense capillaries for fast diffusion; haemoglobin carries poorly soluble oxygen; with too little oxygen, pyruvate becomes 3-carbon lactic acid.

   (i) Because the alveoli are the site of gas exchange, and exchange happens only by diffusion. A dense capillary network gives a very large surface of blood in contact with the air, brings the blood within one cell's thickness of the alveolar air so the diffusion path is extremely short, and — because the blood keeps flowing — keeps carrying oxygen away and bringing carbon dioxide in, so the concentration difference across the wall stays steep. All three make the exchange fast enough for the body's needs. (ii) Because oxygen is only very slightly soluble in blood plasma, so it must be carried by a pigment: haemoglobin, whose iron-containing haem groups have a high affinity for oxygen and bind it reversibly, picking it up in the lungs and releasing it in the tissues. Carbon dioxide, on the other hand, is about twenty times more soluble in plasma, so enough of it can be carried simply dissolved (mainly as bicarbonate) and it needs no pigment. (iii) Because glucose (6 carbon) is first broken down in the cytoplasm by glycolysis into two molecules of pyruvate (3 carbon), a step that needs no oxygen; the complete breakdown of pyruvate to carbon dioxide occurs only in the mitochondria and **requires** oxygen. In human muscles during vigorous exercise oxygen is in short supply, so pyruvate cannot take that route and is instead converted into lactic acid, which is also a 3-carbon molecule. Hence a 3-carbon end product is formed instead of ${\text{CO}}_2$.

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4. Q244 CBSE 2025
   Explain ​how ​urine ​is produced in ​kidneys.
   Show answer

   Urine forms in nephrons by filtration of blood in the glomerulus, then selective reabsorption of useful substances and water in the tubule.

   Urine is made in the nephrons, the filtration units of the kidney. Filtration: blood brought by the renal artery is filtered in the glomerulus inside Bowman's capsule, and water, glucose, amino acids, salts and urea pass into the capsule as the initial filtrate. Selective reabsorption: as the filtrate flows along the tubule, glucose, amino acids, salts and a major amount of water are taken back into the surrounding capillaries, the amount of water depending on the body's needs. The fluid left, mainly water with urea, is urine; it drains through the collecting duct into the ureter and is stored in the urinary bladder.

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5. Q245 CBSE 2025
   Explain ​the ​process of translocation of ​food and ​other ​substances in the phloem ​of plants.
   Show answer

   Sucrose is loaded into the phloem using ATP, water follows by osmosis, and the resulting pressure moves food from source to sink.

   Translocation is the transport of the soluble products of photosynthesis, mainly sucrose, together with amino acids and other substances, through the phloem. It is carried out by the sieve tubes with the help of the companion cells beside them, and unlike transport in the xylem it is an active process that uses energy from ATP. At the source, usually a leaf, sucrose is loaded into the phloem tissue using energy from ATP. This raises the solute concentration inside the sieve tube, so water moves into it by osmosis from the neighbouring xylem. The entry of water builds up a high hydrostatic pressure at the source, and this pressure moves the material in the phloem to the tissues where the pressure is lower, the sinks. At the sink the sucrose is unloaded and used or stored, and the water returns to the xylem. Because the driving force is created within the phloem itself, translocation takes place in both directions, and the plant can send material wherever it is needed; in spring, sugar stored in the root or stem is carried up to the growing buds.

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6. Q246 CBSE 2025
   Differentiate ​between xylem ​and phloem ​on the ​basis of the following :

   1. (i)Direction of transport of ​the substances
   2. (ii)​Major driving forces involved in ​the transport
   3. (iii)Nature of the substance(s) ​transported
   Show answer

   Xylem moves water and minerals upwards passively; phloem moves sucrose and other food both ways using ATP energy.

   (i) Direction of transport: in xylem the transport is unidirectional, water and minerals moving only upwards from the roots to the rest of the plant; in phloem it is bidirectional, the material moving from a source to a sink and so travelling both upwards and downwards. (ii) Major driving forces: in xylem the transport is passive and physical, driven mainly by the transpiration pull created by evaporation of water from the leaves, helped by root pressure, and no ATP is used; in phloem the transport is active, energy from ATP being used to load sucrose into the sieve tube, after which water enters by osmosis and the resulting high hydrostatic pressure drives the solution towards the sink. (iii) Nature of the substances transported: xylem carries water and dissolved inorganic minerals absorbed from the soil, while phloem carries the soluble products of photosynthesis, mainly sucrose, together with amino acids and other organic substances.

   Step-by-step solution →
7. Q247 CBSE 2025
   List three raw ​materials required ​by terrestrial plants ​for ​photosynthesis. ​Explain how nature ​provides these raw ​material to the plants.
   Show answer

   Carbon dioxide from air via stomata, water from soil via roots and xylem, and sunlight from the Sun are the raw materials.

   Three raw materials needed by a land plant for photosynthesis are carbon dioxide, water and sunlight; strictly, carbon dioxide and water are the substances used up, and sunlight supplies the energy. (i) Carbon dioxide: the air around the plant contains carbon dioxide, which diffuses into the leaves through the stomata, tiny pores on the surface of the leaf. (ii) Water: rain keeps the soil moist; the roots absorb water from the soil and the xylem carries it up the stem to the leaves. Mineral salts such as nitrates and magnesium, which the plant also needs, are taken up from the soil along with it. (iii) Sunlight: the Sun provides light, which is absorbed by chlorophyll in the chloroplasts of the leaf cells and converted into chemical energy.

   Step-by-step solution →
8. Q248 CBSE 2025
   Give reasons for ​the following :

   1. (a)Rate of breathing in aquatic animals ​is much faster than terrestrial organisms.
   2. (b)Rings of cartilage are ​present ​in throat of human being.
   3. (c)During ​anaerobic respiration, a $3$ carbon molecule (compound) is ​formed as an end product instead of ${\text{CO}}_2$ in some cells of human ​beings.
   Show answer

   Water holds little dissolved oxygen, cartilage rings keep the windpipe open, and oxygen-starved muscle cells turn pyruvate into 3-carbon lactic acid.

   (a) Aquatic animals take in oxygen dissolved in water, and the amount of dissolved oxygen is fairly low compared with the amount of oxygen in air. To obtain enough oxygen they must pass much more water over their gills, so their rate of breathing is much faster than that of terrestrial organisms. (b) The rings of cartilage in the throat support the wind-pipe (trachea) and ensure that the air passage does not collapse, so air can pass through it freely. (c) In muscle cells that are short of oxygen (for example during sudden, vigorous activity), pyruvate, the $3$-carbon molecule formed from glucose in the cytoplasm, is not broken down to carbon dioxide and water, a process that needs oxygen; instead it is converted into lactic acid, which is also a $3$-carbon molecule. So lactic acid, not carbon dioxide, is the end product.

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9. Q249 CBSE 2025
   1. (i)“The length of the small ​intestine in various animals depends on the food ​they ​eat.” ​Justify the statement.
   2. (ii)Discuss the role of the pancreas and bile juice in the digestion of food in human beings.
   3. (iii)How is the small intestine designed ​to absorb digested ​food ​?
   Show answer

   Herbivores need a longer small intestine; bile makes food alkaline and emulsifies fat, pancreatic enzymes digest the food, and villi absorb it.

   (i) Herbivores such as cattle and deer eat grass, which is rich in cellulose and difficult to digest, so they need a longer small intestine to complete digestion and absorption; carnivores such as tigers eat meat, which is easily and quickly digested, so their small intestine is much shorter. The length therefore depends on how hard the food is to digest, which justifies the statement. (ii) Bile juice, made in the liver and stored in the gall bladder, makes the acidic food coming from the stomach alkaline, because pancreatic enzymes act only in an alkaline medium, and it emulsifies fat, breaking large globules into small droplets so that lipase can act; bile contains no enzymes. The pancreas secretes pancreatic juice containing trypsin, which digests proteins into amino acids, pancreatic amylase, which breaks starch into sugars, and lipase, which breaks emulsified fats into fatty acids and glycerol. (iii) The small intestine is very long and its inner lining bears a very large number of finger-like villi, which greatly increase the surface area for absorption; each villus has a wall only one cell thick and a rich supply of blood vessels, so the digested food passes easily into the blood and is carried to every cell of the body.

   Step-by-step solution →
10. Q250 CBSE 2025
    1. (i)State the ​role ​of ​rings ​of ​cartilage present ​in the throat.
    2. (ii)​Discuss the role of the ribs and diaphragm when air is taken in during the breathing cycle.
    3. (iii)Why do we get muscle cramps during heavy exercise ? Explain.
    Show answer

    Cartilage rings keep the trachea open; the diaphragm and ribs enlarge the chest so air rushes in; oxygen shortage makes lactic acid, causing cramps.

    (i) The C-shaped rings of cartilage in the wall of the wind pipe keep the air passage permanently open; they prevent the trachea from collapsing when the pressure of the air inside it falls, so air can pass freely at all times. (ii) During inhalation the muscles of the diaphragm contract, so the domed diaphragm flattens and moves downwards, and at the same time the muscles between the ribs contract and lift the ribs up and outwards. Both movements increase the volume of the chest cavity, the lungs expand and the pressure inside them falls below atmospheric pressure, so air rushes in through the nostrils and trachea and fills the alveoli. (iii) During heavy exercise the supply of oxygen to the muscle cells falls short of the demand, so the cells respire anaerobically: glucose is broken down to pyruvate in the cytoplasm and the pyruvate is then converted into lactic acid, releasing only a little energy. The lactic acid accumulates in the muscle fibres and causes the pain and cramps; rest and deep breathing supply the oxygen that clears it away.

    Step-by-step solution →
11. Q251 CBSE 2025
    The maintenance functions of all living organisms must go on even when they are not doing anything ​particular. Even when we are just ​sitting in a class or even asleep, this maintenance ​job has ​to go on. These maintenance processes ​require energy to prevent damage and break-down of cells and tissues, which is ​obtained by the individual organism ​from the food prepared by the autotrophs, ​called producers.

    1. (a)Name and define the process by which green plants prepare food.[1]
    2. (b)Write chemical equation involved in the above process.[1]
    3. (c)(i)State in proper sequence the events that occur in synthesis of food by desert plants.[2]
    4. (c)(ii)OR : Explain giving reasons what happens to the rate at which the green plants will prepare food (I) during cloudy weather, and (II) when stomata get blocked due to dust.[2]
    Show answer

    Photosynthesis makes carbohydrate from carbon dioxide and water; desert plants fix carbon dioxide at night; cloudy weather and blocked stomata lower the rate.

    (a) The process is photosynthesis: the process by which green plants (autotrophs) take in carbon dioxide and water and convert them into carbohydrates in the presence of sunlight and chlorophyll, releasing oxygen. (b) $6{\text{CO}}_2+12{\text{H}}_2\text{O}\underset{\text{sunlight}}{\overset{\text{chlorophyll}}{\to }}{\text{C}}_6{\text{H}}_{12}{\text{O}}_6+6{\text{O}}_2+6{\text{H}}_2\text{O}$ (the cancelled form $6{\text{CO}}_2+6{\text{H}}_2\text{O}\to {\text{C}}_6{\text{H}}_{12}{\text{O}}_6+6{\text{O}}_2$ is equally acceptable). (c)(i) At night the stomata open and carbon dioxide is taken in and fixed into an intermediate, which is stored; by day, with the stomata closed, chlorophyll absorbs light energy, that energy becomes chemical energy and water is split into hydrogen and oxygen, and the carbon dioxide from the stored intermediate is reduced to carbohydrate. (c)(ii) (I) During cloudy weather the rate decreases, because less light energy reaches the chlorophyll. (II) When the stomata are blocked by dust the rate decreases, because less carbon dioxide can enter the leaf.

    Step-by-step solution →
12. Q252 CBSE 2024
    In human beings, ​when the process of digestion ​is ​completed, the

    1. (i)​proteins, ​
    2. (ii)carbohydrates, and
    3. (iii)​fats are respectively finally ​converted into :

    1. (a)(i) Amino acids, (ii) glucose and (iii) fatty acids
    2. (b)(i) Amino acids, (ii) glucose, (iii) fatty acids and glycerol
    3. (c)(i) Glucose, (ii) fatty acids and glycerol, (iii) amino acids
    4. (d)(i) Sugars, (ii) amino acids, (iii) fatty acids and glycerol
    Show answer

    (b) (i) Amino acids, (ii) glucose, (iii) fatty acids and glycerol

    Step-by-step solution →
13. Q253 CBSE 2024
    The ​process ​in which transport of soluble products ​of ​photosynthesis takes place ​in plants ​is known ​as :

    1. (a)Transpiration
    2. (b)Evaporation
    3. (c)Conduction
    4. (d)Translocation
    Show answer

    (d) Translocation

    Step-by-step solution →
14. Q254 CBSE 2024
    Which ​of the following statement(s) is (are) true about ​human heart ?

    1. (a)Right atrium receives oxygenated blood from lungs through pulmonary artery.
    2. (b)Left ​atrium transfers ​oxygenated blood to left ventricle ​which sends it to various parts of the body.
    3. (c)Right atrium receives deoxygenated blood through vena cava from ​upper and lower body.
    4. (d)Left atrium transfers oxygenated blood to aorta ​which sends it to different parts of the body.

    1. (a)(a)
    2. (b)(a) and (d)
    3. (c)(b) and (c)
    4. (d)(b) and (d)
    Show answer

    (c) (b) and (c)

    Step-by-step solution →
15. Q255 CBSE 2024
    In ​the human respiratory system, the path taken by ​air ​when we breathe ​in ​is ​:

    1. (a)Nostrils $\to$ Larynx $\to$ Trachea $\to$ Pharynx $\to$ Alveoli
    2. (b)Nostrils $\to$ Trachea $\to$ Larynx $\to$ Pharynx $\to$ Alveoli
    3. (c)Nostrils $\to$ Pharynx $\to$ Larynx $\to$ Trachea $\to$ Alveoli
    4. (d)Nostrils $\to$ Larynx $\to$ Pharynx $\to$ Trachea $\to$ Alveoli
    Show answer

    (c) Nostrils $\to$ Pharynx $\to$ Larynx $\to$ Trachea $\to$ Alveoli

    Step-by-step solution →
16. Q256 CBSE 2024
    The ​opening and ​closing ​of ​stomatal ​pore depends ​upon ​:

    1. (a)temperature
    2. (b)excess of ${\text{CO}}_2$ in the guard cells
    3. (c)high concentration of oxygen in the guard cells
    4. (d)flow of water in and out of the guard cells
    Show answer

    (d) flow of water in and out of the guard cells

    Step-by-step solution →
17. Q257 CBSE 2024
    In ​human ​respiratory ​system, when a person ​breathes ​in, the position of ribs and ​diaphragm will be :

    1. (a)lifted ribs and curve/dome shaped diaphragm.
    2. (b)lifted ribs and flattened diaphragm.
    3. (c)relaxed ribs and flattened diaphragm.
    4. (d)relaxed ribs and curve/dome shaped diaphragm.
    Show answer

    (b) lifted ribs and flattened diaphragm.

    Step-by-step solution →
18. Q258 CBSE 2024
    A stomata closes when :

    1. (i)it needs carbon dioxide for photosynthesis.
    2. (ii)​it ​does not need carbon ​dioxide ​for photosynthesis.
    3. (iii)water flows out of the ​guard cells.
    4. (iv)water flows into the guard cells. The correct ​reason(s) in this ​process is/are :

    1. (a)(i) only
    2. (b)(i) and (iii)
    3. (c)(ii) and (iii)
    4. (d)(ii) and (iv)
    Show answer

    (c) (ii) and (iii)

    Step-by-step solution →
19. Q259 CBSE 2024
    Which of the following statement (s) is (are) true about human heart ​?

    1. (a)​Right atrium receives oxygenated blood from lungs through pulmonary artery.
    2. (b)Left atrium transfers oxygenated blood to left ​ventricle which sends it to various parts of the body.
    3. (c)​Right atrium receives deoxygenated blood from different parts of the body through ​vena cava.
    4. (d)​Left atrium transfers oxygenated blood to aorta ​which sends it to different parts of ​the body.

    1. (a)(b) only
    2. (b)(a) and (d)
    3. (c)(b) and (c)
    4. (d)(b) and (d)
    Show answer

    (c) (b) and (c)

    Step-by-step solution →
20. Q260 CBSE 2024
    An ​organism ​which breaks down the food material ​outside ​the body and then absorbs ​it is ​:

    1. (a)Bread mould
    2. (b)Cuscuta
    3. (c)Lice
    4. (d)Tapeworm
    Show answer

    (a) Bread mould

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