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NCERT Exemplar · Class 10 Science Life Processes

82 questions · 82 still being checked

Multiple Choice Questions 21–30 (part 3 of 9)

  1. Exercise 21

    Choose the correct statement that describes arteries.
    (a)
    They have thick elastic walls, blood flows under high pressure; collect blood from different organs and bring it back to the heart
    (b)
    They have thin walls with valves inside, blood flows under low pressure and carry blood away from the heart to various organs of the body
    (c)
    They have thick elastic walls, blood flows under low pressure; carry blood from the heart to various organs of the body
    (d)
    They have thick elastic walls without valves inside, blood flows under high pressure and carry blood away from the heart to different parts of the body.

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    NCERT’s answer
    (d)
    (d) Thick elastic walls, no valves, high pressure, carrying blood away from the heart to the body. (Thin walls with valves at low pressure, collecting blood back to the heart, describe veins instead.)

  2. Exercise 22

    The filtration units of kidneys are called
    (a)
    ureter
    (b)
    urethra
    (c)
    neurons
    (d)
    nephrons

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    NCERT’s answer
    (d)
    (d) nephrons — each nephron's glomerulus and Bowman's capsule filters blood plasma; the filtrate is refined along the tubule into urine.

  3. Exercise 23

    Oxygen liberated during photosynthesis comes from
    (a)
    water
    (b)
    chlorophyll
    (c)
    carbon dioxide
    (d)
    glucose

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    NCERT’s answer
    (a)
    (a) water — the light reaction splits water; the \(\displaystyle \mathrm{O_2}\) released carries oxygen atoms from \(\displaystyle \mathrm{H_2O}\), confirmed by \(\displaystyle \mathrm{H_2^{18}O}\) tracer experiments, not from \(\displaystyle \mathrm{CO_2}\). \[2\mathrm{H_2O} \xrightarrow{\text{light}} \mathrm{O_2} + 4\mathrm{H^+} + 4e^- \]

  4. Exercise 24

    The blood leaving the tissues becomes richer in
    (a)
    carbon dioxide
    (b)
    water
    (c)
    heamoglobin
    (d)
    oxygen

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    NCERT’s answer
    (a)
    (a) carbon dioxide — tissue cells use \(\displaystyle \mathrm{O_2}\) and release \(\displaystyle \mathrm{CO_2}\) in respiration, so blood leaving them is richer in \(\displaystyle \mathrm{CO_2}\) and poorer in \(\displaystyle \mathrm{O_2}\). \[\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O} + \text{energy} \]

  5. Exercise 25

    Which of the following is an incorrect statement?
    (a)
    Organisms grow with time
    (b)
    Organisms must repair and maintain their structure
    (c)
    Movement of molecules does not take place among cells
    (d)
    Energy is essential for life processes

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    NCERT’s answer
    (c)
    (c) Movement of molecules does not take place among cells — false; diffusion, osmosis and active transport constantly move molecules between and across cells.

  6. Exercise 26

    The internal (cellular) energy reserve in autotrophs is
    (a)
    glycogen
    (b)
    protein
    (c)
    starch
    (d)
    fatty acid

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    NCERT’s answer
    (c)
    (c) starch — plants store surplus photosynthate as starch, an insoluble, osmotically inactive reserve; glycogen is the analogous store in animals, not autotrophs.

  7. Exercise 27

    Which of the following equations is the summary of photosynthesis?
    (a)
    6CO2+12H2O→C6H12O6+6O2+6H2O\displaystyle 6 \mathrm{CO}_2+12 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+6 \mathrm{O}_2+6 \mathrm{H}_2 \mathrm{O}
    (b)
    6CO2+H2O+\displaystyle 6 \mathrm{CO}_2+\mathrm{H}_2 \mathrm{O}+ Sunlight →C6H12O6+O2+6H2O\displaystyle \rightarrow \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+\mathrm{O}_2+6 \mathrm{H}_2 \mathrm{O}
    (c)
    6CO2+12H2O+\displaystyle 6 \mathrm{CO}_2+12 \mathrm{H}_2 \mathrm{O}+ Chlorophyll + Sunlight →C6H12O6+6O2+6H2O\displaystyle \rightarrow \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+6 \mathrm{O}_2+6 \mathrm{H}_2 \mathrm{O}
    (d)
    6CO2+12H2O+\displaystyle 6 \mathrm{CO}_2+12 \mathrm{H}_2 \mathrm{O}+ Chlorophyll + Sunlight →C6H12O6+6CO2+6H2O\displaystyle \rightarrow \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+6 \mathrm{CO}_2+6 \mathrm{H}_2 \mathrm{O}

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    NCERT’s answer
    (c)
    (c) — the only version with correctly balanced coefficients showing both \(\displaystyle \text{chlorophyll}\) and \(\displaystyle \text{sunlight}\) as conditions; (a) omits these conditions, (b) and (d) are unbalanced. \[6\mathrm{CO_2} + 12\mathrm{H_2O} \xrightarrow[\text{Sunlight}]{\text{Chlorophyll}} \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} + 6\mathrm{H_2O} \]

  8. Exercise 28

    Choose the event that does not occur in photosynthesis
    (a)
    Absorption of light energy by chlorophyll
    (b)
    Reduction of carbon dioxide to carbohydrates
    (c)
    Oxidation of carbon to carbon dioxide
    (d)
    Conversion of light energy to chemical energy

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    NCERT’s answer
    (c)
    (c) Oxidation of carbon to \(\displaystyle \mathrm{CO_2}\) — photosynthesis reduces \(\displaystyle \mathrm{CO_2}\) to carbohydrate; it never oxidises carbon back to \(\displaystyle \mathrm{CO_2}\), which instead occurs during respiration. \[\mathrm{CO_2} \xrightarrow{\text{reduction}} \text{carbohydrate} \]

  9. Exercise 29

    The opening and closing of the stomatal pore depends upon
    (a)
    oxygen
    (b)
    temperature
    (c)
    water in guard cells
    (d)
    concentration of CO2\displaystyle \mathrm{CO}_2 in stomata

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    NCERT’s answer
    (c)
    (c) Water in guard cells.Turgor change, not gas levels, drives the pore: \[\text{H}_2\text{O influx into guard cells} \Rightarrow \text{turgor}\uparrow \Rightarrow \text{pore opens} \] \[\text{H}_2\text{O efflux} \Rightarrow \text{turgor}\downarrow \Rightarrow \text{pore closes} \]

  10. Exercise 30

    Choose the forms in which most plants absorb nitrogen
    (i)
    Proteins
    (ii)
    Nitrates and Nitrites
    (iii)
    Urea
    (iv)
    Atmospheric nitrogen
    (a) (i) and (ii)
    (b) (ii) and (iii)
    (c) (iii) and (iv)
    (d) (i) and (iv)

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    NCERT’s answer
    (b)
    (b) (ii) and (iii) — Nitrates/Nitrites and Urea.Roots absorb nitrogen as \(\displaystyle \mathrm{NO_3^-}\)/\(\displaystyle \mathrm{NO_2^-}\) and urea; proteins are too large to absorb, and plants cannot fix atmospheric \(\displaystyle \mathrm{N_2}\).