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SolveItNCERT · CBSE · NEET

NCERT Exemplar · Class 10 Science Our Environment

38 questions · 38 still being checked

Multiple Choice Questions 1–10 (part 1 of 4)

  1. Exercise 1

    Which one of the following is an artificial ecosystem?
    (a)
    Pond
    (b)
    Crop field
    (c)
    Lake
    (d)
    Forest

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    NCERT’s answer
    (b)
    (b) Crop field. A crop field is sown, irrigated and fertilised by humans, so it survives only with continual human input; a pond, a lake and a forest are self-sustaining natural ecosystems.

  2. Exercise 2

    In a food chain, the third trophic level is always occupied by
    (a)
    carnivores
    (b)
    herbivores
    (c)
    decomposers
    (d)
    producers

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    NCERT’s answer
    (a)
    (a) Carnivores. Trophic levels run producer (1st) \(\displaystyle \rightarrow\) herbivore (2nd) \(\displaystyle \rightarrow\) carnivore (3rd); the third level is always occupied by the (primary) carnivores that eat the herbivores.

  3. Exercise 3

    An ecosystem includes
    (a)
    all living organisms
    (b)
    non-living objects
    (c)
    both living organisms and non-living objects
    (d)
    sometimes living organisms and sometimes non-living objects

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    (c)
    (c) Both living organisms and non-living objects. An ecosystem is the functional unit formed by a biotic community (plants, animals, decomposers) interacting with its abiotic surroundings (soil, water, air, sunlight).

  4. Exercise 4

    In the given food chain, suppose the amount of energy at fourth trophic level is 5\displaystyle 5 kJ, what will be the energy available at the producer level?
    Grass → Grasshopper → Frog → Snake → Hawk
    (a)
    5\displaystyle 5 k J
    (b)
    50\displaystyle 50 k J
    (c)
    500\displaystyle 500 k J
    (d)
    5000\displaystyle 5000 k J

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    NCERT’s answer
    (d)
    (d) $\displaystyle 5000$ kJ. By the $\displaystyle 10$% law only a tenth of the energy at one trophic level reaches the next; grass (1st) to snake (4th) is three transfers. \[E_{4} = E_{1}\times(10\%)^{3} \] \[5\ \mathrm{kJ} = E_{1}\times(0.1)^{3} \] \[E_{1} = \dfrac{5\ \mathrm{kJ}}{0.001} = 5000\ \mathrm{kJ} \]

  5. Exercise 5

    Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as
    (a)
    eutrophication
    (b)
    pollution
    (c)
    biomagnification
    (d)
    accumulation

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    NCERT’s answer
    (c)
    (c) Biomagnification. The pesticide is not broken down and is stored in body fat; each consumer eats many contaminated prey, so its concentration rises at every higher trophic level. \[\text{producer} \rightarrow \text{herbivore} \rightarrow \text{carnivore}:\quad \text{trophic level}\uparrow \Rightarrow \text{pesticide concentration}\uparrow \]

  6. Exercise 6

    Depletion of ozone is mainly due to
    (a)
    chlorofluorocarbon compounds
    (b)
    carbon monoxide
    (c)
    methane
    (d)
    pesticides

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    NCERT’s answer
    (a)
    (a) Chlorofluorocarbon compounds. CFCs from aerosols and refrigerants drift to the stratosphere, where UV radiation splits them and the freed chlorine catalytically breaks down ozone molecules.

  7. Exercise 7

    Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called
    (a)
    decomposers
    (b)
    producers
    (c)
    herbivores
    (d)
    carnivores

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    NCERT’s answer
    (b)
    (b) Producers. Green plants trap radiant (solar) energy and fix inorganic \(\displaystyle \mathrm{CO_2}\) and \(\displaystyle \mathrm{H_2O}\) into carbohydrate by photosynthesis, so they form the first trophic level. \[6\mathrm{CO_2} + 6\mathrm{H_2O} \xrightarrow[\text{chlorophyll}]{\text{light}} \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} \]

  8. Exercise 8

    In an ecosystem, the 10\displaystyle 10% of energy available for transfer from one trophic level to the next is in the form of
    (a)
    heat energy
    (b)
    light energy
    (c)
    chemical energy
    (d)
    mechanical energy

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    NCERT’s answer
    (c)
    (c) Chemical energy. \[E_{n+1} = 0.10\,E_n \] The $\displaystyle 10$% passed on stays locked in biomass -- chemical energy; the remaining $\displaystyle 90$% is lost as heat during respiration at each level.

  9. Exercise 9

    Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level constitute the
    (a)
    food web
    (b)
    ecological pyramid
    (c)
    ecosystem
    (d)
    food chain

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    NCERT’s answer
    (a)
    (a) Food web. Several lower-level organisms feeding one higher-level predator link many straight food chains into an interconnected web, not a single chain.

  10. Exercise 10

    Flow of energy in an ecosystem is always
    (a)
    unidirectional
    (b)
    bidirectional
    (c)
    multi directional
    (d)
    no specific direction

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    NCERT’s answer
    (a)
    (a) Unidirectional. Sunlight enters at producers and passes stepwise to consumers, with loss as heat at every transfer -- energy never returns to an earlier trophic level.