Class 10 Science Chapter 13: Our Environment worksheet with answer key
A 20-mark worksheet on Our Environment for about 40 minutes of class or homework: 5 multiple-choice, 3 very short answer and 3 short answer questions, written from the NCERT chapter and checked by a second reviewer. Print the PDF for the class; the answer key carries the marking scheme. Teachers may photocopy it freely.
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Answer: (a) 500 J
Terrestrial green plants capture about 1% of the sunlight falling on their leaves: 1% of 50 000 J = 500 J. 5000 J applies the 10% rule by mistake.
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Answer: (c) fungi and bacteria
Decomposers, the bacteria and fungi, break down dead remains. Deer and boar are herbivores or omnivores, algae are producers, and woodpeckers feed on insects.
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Answer: (c) seaweeds
Seaweeds are green, carry chlorophyll and photosynthesise, so they are producers. Crabs and snails are consumers; fungi are decomposers.
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Answer: (b) third trophic level
Phytoplankton are producers (first), zooplankton herbivores (second), the sardine feeds on them and is at the third level; tuna is fourth.
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Answer: (a) simple inorganic substances that plants take up again
Decomposers break complex organic matter into simple inorganic substances which go into the soil and are used again by plants. Starch is what they break down, not what they return.
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Kulhads are made from clay; making millions of them daily would use up the fertile top-soil, which is needed for crops. So paper cups are used instead.
- making kulhads needs large amounts of clay (1)
- this would cost the fertile top-soil (1)
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Biotic (living): frogs, water lilies. Abiotic (non-living, physical factors): sunlight, dissolved oxygen.
- frogs and water lilies as biotic (1)
- sunlight and dissolved oxygen as abiotic (1)
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Higher-energy UV radiation splits molecular oxygen into free atoms: O₂ → O + O (in the presence of UV). Each free atom then combines with molecular oxygen: O + O₂ → O₃.
- O₂ → O + O, with UV splitting the oxygen molecule (1)
- O + O₂ → O₃ (1)
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Much of it is lost as heat to the environment; some is used in digestion; some is used in doing work (moving, grazing). Only the rest, about 10%, goes into growth and reproduction.
- lost as heat (1)
- used in digestion (1)
- used in doing work (1)
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(i) Composting, since the vegetable waste is biodegradable. (ii) Recycling of the paper and glass. (iii) Landfill in low-lying ground, or incineration at high temperature to ash.
- composting for vegetable waste (1)
- recycling for paper and glass (1)
- landfill or incineration for the residue (1)
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Improvements in life-style mean more is bought and more waste is produced; attitudes have changed, so more of what we use is disposable; and packaging has changed, so much of the waste is now non-biodegradable.
- improved life-style, more waste (1)
- more disposable items (1)
- changed packaging, non-biodegradable (1)