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 20 of 22

1. Q381 CBSE 2020
   1. (a)A gas is released during photosynthesis. Name the gas and also state ​the way ​by which the gas is evolved.
   2. (b)​What are stomata? ​What ​governs the opening and closing of ​stomata ​?
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   Oxygen is released by the splitting of water; stomata are pores whose guard cells swell to open the pore and shrink to close it.

   (a) The gas released during photosynthesis is oxygen. It is evolved by the splitting of water molecules: light energy absorbed by chlorophyll is used to split water into hydrogen and oxygen; the hydrogen is used to reduce carbon dioxide to glucose, and the oxygen is released as oxygen gas, which leaves the leaf through the stomata. (b) Stomata are tiny pores present on the surface of leaves, through which the exchange of gases (during photosynthesis, carbon dioxide in and oxygen out) and the loss of water vapour take place; each pore is bounded by a pair of guard cells. The opening and closing of the stomata is a function of the guard cells: when water flows into the guard cells they swell and the stomatal pore opens; when the guard cells lose water they shrink and the pore closes.

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2. Q382 CBSE 2020
   1. (a)Name the ​organs ​that form ​the excretory system ​in ​human beings.
   2. (b)Describe in brief ​how urine ​is produced in human body.
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   The excretory system has kidneys, ureters, a urinary bladder and a urethra; nephrons filter blood and reabsorb useful substances, leaving urine.

   (a) The excretory system of human beings consists of a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. (b) Urine is produced in the nephrons, the filtration units of the kidneys. Each nephron has a cup-shaped Bowman's capsule containing a bunch of capillaries called the glomerulus. Blood containing nitrogenous wastes is filtered in the glomerulus, and the filtrate collects in Bowman's capsule. As the filtrate flows along the tubule of the nephron, useful substances such as glucose, amino acids, salts and a major amount of water are selectively reabsorbed into the blood capillaries around it. The fluid that remains is urine; the urine formed in each kidney passes through the collecting ducts into the ureter and is carried to the urinary bladder, where it is stored until it is passed out through the urethra.

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3. Q383 CBSE 2020
   1. (a)​Draw a diagram of human alimentary canal and label – gall ​bladder, pancreas, liver and ​small ​intestine on it.
   2. (b)Give ​two reasons to explain why absorption ​of digested food occurs mainly in the ​small intestine.
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   Absorption is mainly in the small intestine because digestion is completed there and its villi give a large surface rich in blood vessels.

   (a) Diagram: the alimentary canal drawn as one continuous tube (mouth, oesophagus, stomach, small intestine, large intestine, rectum, anus) with the four parts labelled: the liver, a large gland in the upper abdomen on the right side of the body; the gall bladder, a small sac under the liver whose bile duct opens into the small intestine; the pancreas, a leaf-like gland below the stomach, in the curve of the first part of the small intestine; and the small intestine, the long coiled tube between the stomach and the large intestine (see the labelled diagram). (b) Any two of these reasons: (1) Digestion of carbohydrates, proteins and fats is completed only in the small intestine, so the food is present here as small soluble molecules that can be absorbed. (2) The inner wall of the small intestine has numerous finger-like projections called villi, which provide a large surface area for absorption. (3) The villi are richly supplied with blood vessels, which carry the absorbed food to different parts of the body. The great length of the coiled small intestine also helps, by keeping the food in contact with the absorbing surface for a long time.

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4. Q384 CBSE 2020
   1. (a)“Blood circulation in ​fishes is different from the ​blood circulation in human ​beings.” Justify ​the statement.
   2. (b)​Describe “blood circulation” in human beings.
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   Fishes have a two-chambered heart and single circulation; humans have a four-chambered heart and double circulation through the lungs and then the body.

   (a) Fishes have a two-chambered heart (one atrium and one ventricle), while human beings have a four-chambered heart (two atria and two ventricles). In fishes the heart pumps deoxygenated blood to the gills, where it is oxygenated, and the blood then passes directly to the body, so it goes through the heart only once in each round: single circulation. In human beings blood goes through the heart twice in each round, once on its way to the lungs and once on its way to the body: double circulation, which keeps oxygenated and deoxygenated blood separate. (b) Deoxygenated blood from all parts of the body is collected by the veins into the vena cava, which pours it into the right atrium. The right atrium passes it to the right ventricle, which pumps it through the pulmonary artery to the lungs. In the lungs the blood gives out carbon dioxide and takes up oxygen. The oxygenated blood returns through the pulmonary vein to the left atrium, which passes it to the left ventricle. The left ventricle pumps it into the aorta, which distributes it through arteries to all parts of the body.

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5. Q385 CBSE 2020
   (a) Draw a diagram of human ​excretory system ​and ​label ​on it the ​following ​parts :

   1. (i)Kidney
   2. (ii)Ureter
   3. (iii)Urinary bladder
   4. (iv)Urethra (b) Write one main function ​each of ​the labelled parts.
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   Kidney filters blood and forms urine, ureter carries it to the urinary bladder, the bladder stores it, and the urethra passes it out.

   (a) The labelled diagram shows a pair of bean-shaped kidneys in the upper abdomen on either side of the backbone, a ureter running from the notch of each kidney down to the urinary bladder in the lower abdomen, and a single urethra leading from the bladder out of the body (the aorta and vena cava, with a renal artery and a renal vein to each kidney, complete the textbook figure). (b) (i) Kidney: filters the blood to remove nitrogenous wastes such as urea, forming urine. (ii) Ureter: carries (transports) urine from the kidney to the urinary bladder. (iii) Urinary bladder: stores urine until it is passed out. (iv) Urethra: carries urine from the bladder out of the body (excretes urine).

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6. Q386 CBSE 2020
   Design ​an ​activity ​to show that ​chlorophyll is ​essential for ​photosynthesis.
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   A destarched variegated leaf kept in sunlight and tested with iodine turns blue-black only where it was green, so chlorophyll is essential.

   Take a potted plant with variegated leaves; keep it in a dark room for three days to use up its starch, then in sunlight for about six hours. Pluck a leaf and trace its green areas on paper. Dip it in boiling water for a few minutes, then heat it in alcohol placed in a water bath until the alcohol boils (the chlorophyll dissolves). Dip it in dilute iodine solution for a few minutes and rinse it. Observation: only the parts that were green turn blue-black. Inference: starch, made by photosynthesis, forms only where chlorophyll is present, so chlorophyll is essential for photosynthesis.

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7. Q387 CBSE 2019
   Name ​an ​enzyme ​present in pancreatic ​juice.
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   Trypsin, which digests proteins, is an enzyme of pancreatic juice; lipase is another.

   Trypsin, which digests proteins. Lipase, which breaks down emulsified fats, is also present in pancreatic juice and is equally correct.

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8. Q388 CBSE 2019
   What will happen ​if mucus is ​not ​secreted ​by the gastric ​glands ?
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   Without mucus, the acid and pepsin would damage the stomach lining, causing acidity and ulcers.

   The inner lining of the stomach would no longer be protected from the hydrochloric acid of the gastric juice. The acid (together with pepsin) would damage the lining, causing acidity and ulcers in the stomach.

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9. Q389 CBSE 2019
   What causes ​movement of ​food inside the ​alimentary ​canal in ​human beings ?
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   Peristalsis, the rhythmic contraction and relaxation of the muscles in the wall of the alimentary canal, pushes the food forward.

   Peristalsis (peristaltic movements): the muscles in the wall of the alimentary canal contract and relax rhythmically, and this wave of contraction pushes the food forward along the canal.

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10. Q390 CBSE 2019
    Write ​two different ways ​in which ​glucose ​is oxidized ​to provide energy in human body. Write the products formed ​in each ​case.
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    Aerobic respiration (with oxygen) gives carbon dioxide and water; anaerobic respiration (lack of oxygen, in muscles) gives lactic acid.

    (1) Aerobic respiration, in the presence of oxygen (in the mitochondria): glucose $\to$ pyruvate $\to$ carbon dioxide + water + energy. Products: carbon dioxide and water. (2) Anaerobic respiration, when there is a lack of oxygen (in muscle cells during hard exercise): glucose $\to$ pyruvate $\to$ lactic acid + energy. Product: lactic acid.

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11. Q391 CBSE 2019
    How ​is ${\text{O}}_2$ and ${\text{CO}}_2$ transported in ​human ​beings?
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    Oxygen is carried by haemoglobin in red blood cells; carbon dioxide, being more soluble, travels mostly dissolved in the plasma.

    Oxygen is carried by haemoglobin, the respiratory pigment present in the red blood cells. Haemoglobin has a very high affinity for oxygen: it takes up oxygen in the lungs and releases it in the tissues. Carbon dioxide is more soluble in water than oxygen, so it is transported mostly in dissolved form in the blood plasma, from the tissues to the lungs, where it is breathed out.

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12. Q392 CBSE 2019
    List two ​different ​functions ​performed by ​pancreas ​in our ​body.
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    It secretes pancreatic juice with digestive enzymes into the small intestine and the hormone insulin into the blood.

    (i) Digestive function: The pancreas secretes pancreatic juice into the small intestine. It contains enzymes such as trypsin, which digests proteins, and lipase, which breaks down emulsified fats. (ii) Hormonal function: The pancreas secretes hormones such as insulin (and glucagon) directly into the blood; insulin regulates the blood sugar level.

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13. Q393 CBSE 2019
    List ​in ​tabular form two ​differences ​between ​pepsin ​and ​trypsin.
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    Pepsin comes from the gastric glands and acts in an acidic medium; trypsin comes from the pancreas and acts in an alkaline medium.

    (i) Source: Pepsin is secreted by the gastric glands of the stomach (in gastric juice); trypsin is secreted by the pancreas (in pancreatic juice). (ii) Medium: Pepsin acts in an acidic medium, provided by hydrochloric acid in the stomach; trypsin acts in an alkaline (basic) medium in the small intestine.

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14. Q394 CBSE 2019
    List two types ​of the ​transport ​system ​in human beings and write ​the functions of any ​one of these.
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    Blood circulatory system and lymphatic system; blood carries oxygen, carbon dioxide, digested food, wastes, salts and hormones.

    The two types of transport system are the blood circulatory system (heart, blood vessels and blood) and the lymphatic system (lymph, lymph vessels and lymph nodes). Functions of the blood circulatory system: blood carries oxygen from the lungs to all the cells; it carries carbon dioxide from the cells to the lungs; it carries digested food from the small intestine to all the cells; and it carries nitrogenous wastes such as urea to the kidneys. It also transports salts and hormones. If the lymphatic system is chosen instead: lymph carries digested and absorbed fat from the small intestine, and it drains excess tissue fluid from the spaces between cells back into the blood.

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15. Q395 CBSE 2019
    Write ​three ​types of blood vessels. ​Give ​one important feature of ​each.
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    Arteries have thick elastic walls, veins have thin walls with valves, and capillaries have walls one cell thick.

    (1) Arteries: carry blood away from the heart to the organs; they have thick, elastic walls because the blood in them is under high pressure. (2) Veins: carry blood from the organs back to the heart; they have thin walls and valves that let the blood flow in one direction only. (3) Capillaries: the finest blood vessels, with walls one cell thick, across which materials are exchanged between the blood and the body cells.

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16. Q396 CBSE 2019
    Define ​the term transpiration. ​Design an ​experiment ​to ​demonstrate ​this process.
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    Transpiration is loss of water vapour from aerial parts, mainly leaves; droplets inside a bag tied over a leafy shoot demonstrate it.

    Transpiration is the loss of water in the form of vapour from the aerial parts of a plant, mainly through the stomata of its leaves. Experiment: (1) Take a healthy, well-watered potted plant. (2) Cover the soil in the pot with a plastic sheet so that no water evaporates from it. (3) Enclose the leafy shoot in a dry, transparent polythene bag and tie it tightly round the base of the stem. (4) Keep the set-up in bright sunlight for about half an hour. Observation: droplets of water appear on the inner surface of the bag (a similar set-up with the leaves removed stays almost dry). Conclusion: the leaves have given out water vapour, which condensed on the bag; this demonstrates transpiration.

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17. Q397 CBSE 2019
    List four ​functions of the human heart. ​Why is double circulation ​necessary ​in the ​human ​body ?
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    The heart receives and pumps blood to lungs and body; double circulation keeps oxygenated and deoxygenated blood separate for efficient oxygen supply.

    Four functions of the human heart: (i) Its right atrium receives deoxygenated blood from the body (through the vena cava). (ii) Its right ventricle pumps this deoxygenated blood to the lungs for oxygenation (through the pulmonary artery). (iii) Its left atrium receives oxygenated blood from the lungs (through the pulmonary veins). (iv) Its left ventricle pumps the oxygenated blood to all parts of the body (through the aorta). Double circulation is necessary because it keeps oxygenated and deoxygenated blood separate: blood passes through the heart twice in each round, once to go to the lungs and once to go to the body. This gives a highly efficient supply of oxygen to the body, which humans need because of their high energy needs; they constantly use energy to maintain their body temperature.

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18. Q398 CBSE 2019
    List in ​tabular ​form ​three ​distinguishing ​features ​between autotrophic nutrition and heterotrophic nutrition.
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    Autotrophs make their own food from carbon dioxide and water using sunlight and store starch; heterotrophs depend on others for food and store glycogen.

    Autotrophic nutrition versus heterotrophic nutrition: 1. The organism can make its own food, versus the organism cannot make its own food. 2. It needs carbon dioxide and water, in the presence of sunlight and chlorophyll, to prepare food, versus it depends on plants and animals, directly or indirectly, for ready-made food. 3. It stores food in the form of starch, versus it stores food in the form of glycogen. Examples: green plants and some bacteria are autotrophs; animals, fungi and most bacteria are heterotrophs. Any other correct pair of features also earns credit.

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19. Q399 CBSE 2019
    Explain ​the ​ways ​in ​which glucose ​is ​broken down ​in absence or shortage of oxygen.
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    Glucose first becomes pyruvate in the cytoplasm; without enough oxygen, pyruvate gives ethanol and ${\text{CO}}_2$ in yeast or lactic acid in muscle cells.

    First step (common to both): In the cytoplasm, glucose, a six-carbon molecule, is broken down into pyruvate, a three-carbon molecule, and a little energy is released. (i) In the absence of oxygen (as in yeast, during fermentation), pyruvate is converted into ethanol and carbon dioxide, and energy is released. This is anaerobic respiration: $\text{Glucose}\stackrel{\text{in cytoplasm}}{\to }\text{Pyruvate}+\text{energy}\stackrel{\text{absence of oxygen (in yeast)}}{\to }\text{Ethanol}+{\text{CO}}_2+\text{energy}$ (ii) When there is a shortage of oxygen (as in our muscle cells during vigorous activity), pyruvate is converted into lactic acid, a three-carbon molecule, and energy is released. The build-up of lactic acid in the muscles causes cramps: $\text{Glucose}\stackrel{\text{in cytoplasm}}{\to }\text{Pyruvate}+\text{energy}\stackrel{\text{lack of oxygen (in muscle cells)}}{\to }\text{Lactic acid}+\text{energy}$ In both cases much less energy is released than in aerobic respiration, because glucose is not broken down completely.

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20. Q400 CBSE 2019
    1. (a)​List ​in ​tabular form ​two differentiating features between xylem and phloem.
    2. (b)Write two ​advantages of ​transpiration in ​plants.
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    Xylem carries water and minerals one way, upwards; phloem carries food both ways; transpiration pulls water up and cools the leaves.

    (a) (i) Material carried: xylem carries water and dissolved minerals; phloem carries food, the products of photosynthesis. (ii) Direction: in xylem, transport is one way, upwards from the roots to the leaves; in phloem, it is both ways, upwards and downwards. (b) (i) Transpiration creates a suction, the transpiration pull, which helps in the absorption and upward movement of water and dissolved minerals from the roots to the leaves. (ii) It helps in temperature regulation, keeping the leaves cool.

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