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 22 of 22

1. Q421 CBSE 2019
   In the ​experimental set-up to show that ​“the ​germinating seeds give out carbon dioxide”, answer the following questions :

   1. (i)Why do we keep the conical flask airtight ?
   2. (ii)Name ​the ​substance ​kept in the small test tube inside the conical flask. Write its role.
   3. (iii)Why ​does water rise in the delivery tube ?
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   The flask is kept airtight; KOH absorbs the carbon dioxide, creating a partial vacuum, so air pressure pushes water up the delivery tube.

   (i) The flask is kept airtight so that the carbon dioxide given out by the germinating seeds cannot escape and outside air (with its oxygen) cannot enter; any change in the gas inside is then due only to the seeds. (ii) Potassium hydroxide ($\text{KOH}$) solution. Role: it absorbs the carbon dioxide given out by the germinating seeds. (iii) $\text{KOH}$ absorbs the carbon dioxide, so the amount of gas in the flask decreases and a partial vacuum is created (the pressure inside falls). The air pressure on the water in the beaker then pushes water up the delivery tube.

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2. Q422 CBSE 2018
   1. (a)Why ​do fishes die when taken out of ​water ?
   2. (b)Leaves of a healthy potted ​plant were coated with ​Vaseline. Will this plant ​remain healthy for long ? Give reason to ​justify your answer.
   3. (c)If ​a plant is releasing ${\text{CO}}_2$ and taking in ${\text{O}}_2$ during the day, does it mean that there is no photosynthesis occurring ? Give ​reason for your answer.
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   Fish gills cannot absorb oxygen from air; Vaseline blocks the stomata so the plant dies; photosynthesis still occurs but is slower than respiration.

   (a) Fishes respire through gills, which take in the oxygen dissolved in water. Out of water the gills cannot take in oxygen from the air (their thin filaments collapse and dry up), so the fish cannot respire and dies. (b) No, the plant will not remain healthy for long. The Vaseline covers the stomata, so the exchange of gases stops: carbon dioxide cannot enter the leaves, photosynthesis stops and the plant cannot make its food. Transpiration also stops, so the upward pull of water and minerals slows down. The plant will weaken and die. (c) No, it does not mean that there is no photosynthesis. Respiration goes on all the time, and during the day the ${\text{CO}}_2$ released in respiration is taken up in photosynthesis. A plant that still releases ${\text{CO}}_2$ and takes in ${\text{O}}_2$ in the day is photosynthesising more slowly than it respires (as in dim light): photosynthesis is occurring, but it uses up only part of the ${\text{CO}}_2$ produced in respiration.

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3. Q423 CBSE 2018
   1. (a)Write the name of different components of transport system in ​human beings and state their ​functions in brief.
   2. (b)How is blood ​clot form, if ​a ​leak develops in the system ​of ​blood vessels ?
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   The transport system has the heart, blood vessels, blood and lymph; platelets and fibrin threads form a clot that seals a leak.

   (a) The transport (circulatory) system of human beings has these components: (i) Heart: a muscular pump with four chambers. Its right side (right atrium and right ventricle) receives deoxygenated blood from the body and pumps it to the lungs; its left side (left atrium and left ventricle) receives oxygenated blood from the lungs and pumps it to the whole body. (ii) Blood vessels: arteries carry blood away from the heart to the organs (thick, elastic walls for the high pressure); veins collect blood from the organs and bring it back to the heart (valves keep it flowing one way); capillaries, with walls one cell thick, allow materials to be exchanged between the blood and the surrounding cells. (iii) Blood: a fluid connective tissue. Plasma transports food, carbon dioxide and nitrogenous wastes in dissolved form; red blood cells carry oxygen (with haemoglobin); white blood cells fight infection; platelets help in clotting. (iv) Lymph: a fluid that drains the excess tissue fluid back into the blood and carries digested and absorbed fat from the intestine. (b) When a blood vessel develops a leak, the platelets circulating in the blood gather at the point of injury and plug the leak by helping the blood to clot there. The platelets and the injured tissue release clotting factors; the plasma protein prothrombin is changed into thrombin (calcium ions are needed), and thrombin changes the soluble plasma protein fibrinogen into insoluble fibrin threads. The fibrin threads form a mesh that traps blood cells, forming a clot that seals the leak, stops the loss of blood and helps to maintain the blood pressure.

   Step-by-step solution →
4. Q424 CBSE 2018
   1. (a)​Mention any two components of blood.
   2. (b)Trace the ​movement of ​oxygenated blood in the body.
   3. (c)Write the function ​of valves present in ​between atria and ventricles.
   4. (d)Write ​one structural difference between the composition ​of artery and veins.
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   Oxygenated blood flows from the lungs via the left atrium and ventricle to the aorta; valves stop backflow; arteries have thicker walls than veins.

   (a) Any two of these: plasma, red blood cells (RBCs), white blood cells (WBCs) and platelets. (b) $\text{lungs}\to \text{pulmonary veins}\to \text{left atrium}\to \text{left ventricle}\to \text{aorta}\to \text{arteries}\to \text{capillaries of the body organs}$. Oxygen-rich blood from the lungs enters the left atrium through the pulmonary veins; the left atrium contracts and passes it into the left ventricle, which contracts and pumps it through the aorta to all the organs of the body. (c) The valves between the atria and the ventricles prevent the backflow of blood: they let blood pass only from the atria into the ventricles, and close when the ventricles contract. (d) An artery has a thick, elastic wall, while a vein has a thin wall. (Or: veins have valves along their length, arteries do not.)

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5. Q425 CBSE 2018
   1. (a)Write the reaction that occurs when glucose breaks down anaerobically in yeast.
   2. (b)​Write the mechanism by ​which fishes ​breath in water.
   3. (c)Name the balloon likes ​structures present ​in lungs. List its two functions.
   4. (d)Name the respiratory pigment and write ​its role ​in human beings.
   Show answer

   Yeast makes ethanol and carbon dioxide; fish absorb dissolved oxygen at the gills; alveoli exchange gases; haemoglobin carries oxygen.

   (a) In yeast, glucose (a 6-carbon molecule) is first broken down in the cytoplasm into pyruvate (a 3-carbon molecule), releasing a little energy; in the absence of oxygen, pyruvate is then converted into ethanol and carbon dioxide (fermentation): $\text{Glucose}\stackrel{\text{in cytoplasm}}{\to }\text{Pyruvate}+\text{Energy}\underset{\text{in yeast}}{\overset{\text{absence of oxygen}}{\to }}\text{Ethanol}+\text{Carbon dioxide}+\text{Energy}$ Overall: ${\text{C}}_6{\text{H}}_{12}{\text{O}}_6\to 2{\text{C}}_2{\text{H}}_5\text{OH}+2{\text{CO}}_2+\text{Energy}$ (b) Fishes use the oxygen dissolved in water. A fish takes in water through its mouth and forces it over the gills, which are richly supplied with blood capillaries; the dissolved oxygen diffuses from the water into the blood, and carbon dioxide diffuses from the blood into the water, which passes out through the gill openings. As water contains much less dissolved oxygen than air, fishes breathe much faster than terrestrial animals. (c) The balloon-like structures are the alveoli (singular: alveolus). Functions: 1. They provide a very large surface area for the exchange of gases. 2. Their thin walls, with an extensive network of blood capillaries, allow oxygen from the inhaled air to diffuse into the blood and carbon dioxide from the blood to diffuse into the alveolar air, to be breathed out. (d) The respiratory pigment in human beings is haemoglobin, present in the red blood cells. Role: it has a very high affinity for oxygen; it takes up oxygen from the air in the lungs and carries it to the tissues, which are deficient in oxygen.

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6. Q426 CBSE 2018
   1. (a)Define excretion.
   2. (b)Name ​the basic filtration unit present in the kidney.
   3. (c)Draw excretory system in ​human beings ​and ​label the following ​organs of excretory system ​which perform following functions : (i) ​form urine. (ii) is a long tube which collects urine from kidney. (iii) store urine ​until it is passed out.
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   Excretion removes harmful metabolic wastes; the nephron is the filtration unit; the kidney forms urine, the ureter carries it and the bladder stores it.

   (a) Excretion is the biological process by which harmful metabolic wastes, especially nitrogenous wastes such as urea, are removed from the body. (b) Nephron. (c) Diagram of the human excretory system (see the figure): a pair of kidneys, a pair of ureters, the urinary bladder and the urethra, labelled: (i) Kidney: forms urine. (ii) Ureter: the long tube that collects urine from the kidney and carries it to the urinary bladder. (iii) Urinary bladder: stores urine until it is passed out through the urethra.

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7. Q427 CBSE 2018
   1. (a)Name the process and explain the type ​of nutrition found in green ​plants. ​List the raw materials required ​for this ​process. Give chemical equation ​for the mentioned process.
   2. (b)​Write three events that occur during this process.
   Show answer

   Green plants make their own food by photosynthesis (autotrophic nutrition) from carbon dioxide and water using sunlight, in three main events.

   (a) The process is photosynthesis. Green plants show autotrophic nutrition: they make their own food (carbohydrates such as glucose) from simple inorganic substances, carbon dioxide and water, using the energy of sunlight absorbed by chlorophyll; the food not used at once is stored as starch. Raw materials: carbon dioxide (from the air, through the stomata) and water (from the soil, through the roots); sunlight and chlorophyll are also needed. Equation: $6{\text{CO}}_2+12{\text{H}}_2\text{O}\underset{\text{Chlorophyll}}{\overset{\text{Sunlight}}{\to }}{\text{C}}_6{\text{H}}_{12}{\text{O}}_6+6{\text{O}}_2+6{\text{H}}_2\text{O}$ (b) (i) Absorption of light energy by chlorophyll. (ii) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen. (iii) Reduction of carbon dioxide to carbohydrates.

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8. Q428 CBSE 2018
   List the ​steps ​of preparation ​of temporary mount of a leaf peel ​to ​observe ​stomata.
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   Take a thin leaf peel, stain it with safranin, mount it in glycerine under a cover slip and observe it.

   Steps: (i) Remove a thin peel from the lower surface of a leaf (by tearing it obliquely or with forceps) and keep it in water. (ii) Stain the peel with safranin for a short time and wash off the extra stain. (iii) Put the stained peel on a clean glass slide. (iv) Mount it in a drop of glycerine and place a cover slip over it gently with a needle, avoiding air bubbles; then observe it under the microscope.

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9. Q429 CBSE 2018
   Draw ​a labelled diagram of the experimental set ​up for ​the ​study ​of liberation of carbon ​dioxide gas ​during respiration.
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   Draw a flask with germinating seeds and a KOH tube, closed by a cork with a bent delivery tube dipping into water.

   The labelled diagram is the figure at step 3. Its parts: (i) A conical flask with germinating seeds placed on moist cotton. (ii) A small test tube containing KOH solution, hung inside the flask by a thread from the cork. (iii) An airtight cork closing the flask. (iv) A bent glass (delivery) tube passing through the cork, one end opening into the flask and the other end dipping into water in a beaker. (v) The water rising in the bent tube after some time, because the KOH absorbs the carbon dioxide given out by the respiring seeds.

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10. Q430 CBSE 2018
    In the experiment ​of preparing a temporary mount ​of a leaf ​peel to observe stomata, we use glycerine and safranin. ​State ​the ​role of the two ​liquids in this case.
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    Glycerine prevents the peel from drying; safranin stains the cells so that guard cells and stomata are seen clearly.

    Glycerine: keeps the leaf peel moist and prevents it from drying up while it is observed under the microscope. Safranin: a stain; it colours the cells of the peel (their walls and nuclei), so that the epidermal cells, the guard cells and the stomata become distinct and are seen clearly.

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11. Q431 CBSE 2018
    Your friend is preparing ​a temporary mount of a leaf ​peel ​to observe stomata. At ​which stage of preparation, should ​he use a stain and glycerine. State ​the role ​of these two liquids.
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    Stain (safranin) is used after the peel is taken, to colour the cells; glycerine is used at mounting, to stop the peel drying.

    Stain (safranin): used after the peel is taken from the leaf and placed in water, before it is mounted. The peel is kept in a few drops of dilute safranin for about a minute and the extra stain is washed off. Role: it colours the cell walls and nuclei, so that the epidermal cells, guard cells and stomata are clearly visible. Glycerine: used at the mounting stage. The stained peel is placed on a clean slide in a drop of glycerine and then covered with a coverslip. Role: it prevents the peel from drying up while it is observed.

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