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NCERT Exemplar · Class 9 Science Natural Resources

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Multiple Choice Questions 21–30 (part 3 of 6)

  1. Exercise 21

    Total earth’s surface covered by water is
    (a)
    75\displaystyle 75%
    (b)
    60\displaystyle 60%
    (c)
    85\displaystyle 85%
    (d)
    50\displaystyle 50%

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    NCERT’s answer
    (a)
    (a) $\displaystyle 75$%. About three-fourths of the earth's surface is ocean and other water bodies, leaving roughly a quarter as land.

  2. Exercise 22

    Biotic component of biosphere is not constituted by
    (a)
    producers
    (b)
    consumers
    (c)
    decomposer
    (d)
    air

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    NCERT’s answer
    (d)
    (d) Air. Producers, consumers and decomposers are living organisms and so are biotic; air is a physical, non-living component of the biosphere, hence abiotic.

  3. Exercise 23

    An increase in carbondioxide content in the atmosphere would not cause
    (a)
    more heat to be retained by the environment
    (b)
    increase in photosynthesis in plants
    (c)
    global warming
    (d)
    abundance of desert plants

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    NCERT’s answer
    (d)
    (d) Abundance of desert plants. More \(\displaystyle \text{CO}_2\) does trap heat, warm the planet and speed up photosynthesis: \[\text{CO}_2\uparrow \;\Rightarrow\; \text{heat trapped}\uparrow \;\Rightarrow\; T_{\text{global}}\uparrow \] desert-plant abundance depends on rainfall and aridity, not on atmospheric \(\displaystyle \text{CO}_2\).

  4. Exercise 24

    Oxygen is returned to the atmosphere mainly by
    (a)
    burning of fossil fuel
    (b)
    respiration
    (c)
    photosynthesis
    (d)
    fungi

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    NCERT’s answer
    (c)
    (c) Photosynthesis. It is the only process among the options that produces oxygen rather than consuming it: \[6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{sunlight, chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \] combustion, respiration and fungal decomposition all use up oxygen.

  5. Exercise 25

    Low visibility during cold weather is due to
    (a)
    formation of fossil fuel
    (b)
    unburnt carbon particles or hydrocarbons suspended in air
    (c)
    lack of adequate power supply
    (d)
    none of these

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    NCERT’s answer
    (b)
    (b) Unburnt carbon particles or hydrocarbons suspended in air. Cold air traps smoke and soot near the ground (temperature inversion), scattering light and cutting visibility as smog.

  6. Exercise 26

    Growth of Lichens on barren rocks is followed by the growth of
    (a)
    moss
    (b)
    ferns
    (c)
    gymnosperms
    (d)
    algae

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    NCERT’s answer
    (a)
    (a) Moss. Lichens are pioneers that weather bare rock into a thin soil layer; mosses colonise this soil next, ahead of ferns and larger plants.

  7. Exercise 27

    Marked temperature changes in aquatic environment can affect
    (a)
    breeding of animals
    (b)
    more growth of aquatic plants
    (c)
    process of digestion in animals
    (d)
    availability of nutrients.
    NAT URAL RESOURCES

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    NCERT’s answer
    (a)
    (a) Breeding of animals. Spawning and reproductive cycles of many aquatic species are cued by water temperature, so a marked change disrupts their breeding.

  8. Exercise 28

    Soil erosion can be prevented by
    (a)
    raising forests
    (b)
    deforestation
    (c)
    excessive use of fertilizer
    (d)
    overgrazing by animals

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    NCERT’s answer
    (a)
    (a) Raising forests. Tree and vegetation cover binds soil with roots and slows runoff, so rain and wind carry away far less topsoil.

  9. Exercise 29

    What happens when rain falls on soil without vegetational cover?
    (a)
    Rain water percolates in soil efficiently
    (b)
    Rain water causes loss of surface soil
    (c)
    Rain water leads to fertility of the soil
    (d)
    Rain water does not cause any change in soil

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    NCERT’s answer
    (b)
    (b) Rain water causes loss of surface soil. With no roots to bind the particles, flowing rainwater carries away the exposed, fertile topsoil.

  10. Exercise 30

    Oxygen is harmful for
    (a)
    ferns
    (b)
    nitrogen fixing bacteria
    (c)
    chara
    (d)
    mango tree

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    NCERT’s answer
    (b)
    (b) Nitrogen fixing bacteria. Nitrogenase, the enzyme these bacteria use to fix atmospheric \(\displaystyle \text{N}_2\), is inactivated by oxygen, so fixation needs anaerobic conditions.