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Class 10 · Science · Chapter 13: Our Environment

BSEB Class 10 Science Chapter 13: Objective Questions (MCQ) with Answers

Bihar Board · NCERT · CBSE

All 55 objective questions (MCQ) of this chapter — solve first, then tap “Show answer”. Each question shows its source label: «BSEB 2025 · board paper» = verified from the official board paper; «Board-style (practice)» = Study With Me's own practice questions.

← Chapter 13: Our Environment — full notes, video, questions

1Check

Which of these is a human-made ecosystem?

  1. (A) A lake
  2. (B) A forest
  3. (C) A crop-field
  4. (D) A pond
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Correct answer: (C) A crop-field

A crop-field and a garden are human-made. A forest, a pond and a lake are natural.

2Check

Who breaks dead organisms into simple substances?

  1. (A) Only producers
  2. (B) Decomposers
  3. (C) Only abiotic soil
  4. (D) Only herbivores
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Correct answer: (B) Decomposers

Decomposers break them down. Without them the garbage stays piled up.

3Check

Which of the following is a food chain?

  1. (A) Grass, wheat and mango
  2. (B) Grass, goat and human
  3. (C) Goat, cow and elephant
  4. (D) Grass, fish and goat
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Correct answer: (B) Grass, goat and human

Grass → goat → human is a chain. Grass, wheat and mango are all producers.

4Check

About what part of the sunlight on the leaves do plants turn into food?

  1. (A) 1 percent
  2. (B) 10 percent
  3. (C) 50 percent
  4. (D) 100 percent
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Correct answer: (A) 1 percent

About 1 percent. Ten percent is the share that reaches the next consumer.

5Check

A food web forms because —

  1. (A) Energy comes back
  2. (B) One organism is usually eaten by several kinds
  3. (C) There are only two levels
  4. (D) There are no decomposers
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Correct answer: (B) One organism is usually eaten by several kinds

Each organism is usually eaten by two or more kinds, so a web forms.

6Check

In biological magnification, where is the amount of a harmful chemical the greatest?

  1. (A) In the producers
  2. (B) In the water, before any organism
  3. (C) At the top of the chain
  4. (D) Zero in the soil
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Correct answer: (C) At the top of the chain

The amount is greatest at the top.

7Check

A pesticide enters the chain when —

  1. (A) Plants take it from soil or water
  2. (B) Ozone breaks
  3. (C) Decomposers eat it at once
  4. (D) It is made only by sunlight
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Correct answer: (A) Plants take it from soil or water

The chemical is washed into soil or water and plants absorb it.

8Check

High in the atmosphere the main job of ozone is —

  1. (A) To supply the oxygen we breathe
  2. (B) To shield us from UV rays
  3. (C) To break pesticides
  4. (D) To make food
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Correct answer: (B) To shield us from UV rays

High ozone shields us from UV. Near the ground the same molecule is poisonous.

9Check

CFCs were mainly used —

  1. (A) As decomposers in a food chain
  2. (B) In refrigerators and fire extinguishers
  3. (C) In an aquarium aerator
  4. (D) Only in clay kulhads
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Correct answer: (B) In refrigerators and fire extinguishers

CFCs were used as refrigerants and in fire extinguishers.

10Check

Which group contains a non-biodegradable item?

  1. (A) Grass, flowers and leather
  2. (B) Fruit peels, cake and lime juice
  3. (C) Grass, wood and plastic
  4. (D) Cake, wood and grass
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Correct answer: (C) Grass, wood and plastic

Plastic is non-biodegradable. Peels, cake and grass are biodegradable.

11Check

Substances broken down by biological processes are called —

  1. (A) Non-biodegradable
  2. (B) Biodegradable
  3. (C) Only CFCs
  4. (D) Only abiotic
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Correct answer: (B) Biodegradable

They are called biodegradable.

12Check

Which is an environment-friendly habit?

  1. (A) Only a cloth bag
  2. (B) Only switching off an idle fan
  3. (C) Only walking to school
  4. (D) All three
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Correct answer: (D) All three

All three are environment-friendly.

13Check

An example of a local body is —

  1. (A) Only the Sun
  2. (B) A panchayat or a municipal corporation
  3. (C) Only the ozone layer
  4. (D) Only one insect
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Correct answer: (B) A panchayat or a municipal corporation

A panchayat, a municipal corporation or a resident welfare association is a local body.

14Check

E-waste thrown in the open is harmful because —

  1. (A) It at once becomes compost completely
  2. (B) Poisonous metals from batteries and circuits can reach soil and water
  3. (C) It builds the ozone layer
  4. (D) It only blocks sunlight
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Correct answer: (B) Poisonous metals from batteries and circuits can reach soil and water

Metals such as lead and mercury can reach the soil and the water.

15BSEB 2025 · board paper · Q78 · page 251 mark

An example of micro-consumer is—

  1. (A) Bacteria
  2. (B) Fungus
  3. (C) Algae
  4. (D) Both (A) and (B)
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Correct answer: (D) Both (A) and (B)

Bacteria and fungi break dead organisms and waste into simple inorganic substances — they are decomposers (micro-consumers). Algae are green, so they are producers (lesson 1).

16BSEB 2025 · board paper · Q79 · page 251 mark

Carnivorous animals are called—

  1. (A) Primary consumer
  2. (B) Secondary consumer
  3. (C) Tertiary consumer
  4. (D) Both (A) and (B)
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Correct answer: (B) Secondary consumer

Herbivores = primary consumers. The carnivores that eat them = secondary consumers (large carnivores can also sit at the tertiary level, but the expected answer here is (B)). (A) is wrong, so (D) is wrong too (lesson 2).

17BSEB 2025 · board paper · Q80 · page 261 mark

What percentage of total energy is transferred to the next trophic level at each trophic level of the food chain?

  1. (A) 0.1%
  2. (B) 01%
  3. (C) 10%
  4. (D) 100%
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Correct answer: (C) 10%

Ten percent law: on average only about 10% of the food eaten becomes the body of the next level; the rest goes in heat, digestion and work (lesson 2).

18BSEB model paper 2026 (not the annual exam) · Q56 · page 191 mark

Which of the following substance is decomposed by biological process?

  1. (A) Dead grass and leaves
  2. (B) Polythene
  3. (C) Rubber
  4. (D) None of these
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Correct answer: (A) Dead grass and leaves

Dead grass and leaves are biodegradable — bacteria and fungi break them down. Polythene is non-biodegradable (lesson 5).

19BSEB model paper 2026 (not the annual exam) · Q78 · page 251 mark

Which of the following comes under environment?

  1. (A) Hydrosphere
  2. (B) Lithosphere
  3. (C) Atmosphere
  4. (D) All of these
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Correct answer: (D) All of these

The environment is everything around organisms — water, land (soil, minerals) and air; these are the abiotic components of an ecosystem (lesson 1).

20BSEB model paper 2026 (not the annual exam) · Q79 · page 251 mark

What type of consumer is frog in the field ecosystem?

  1. (A) Primary
  2. (B) Secondary
  3. (C) Tertiary
  4. (D) Quaternary
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Correct answer: (B) Secondary

Grass → grasshopper (primary) → frog (secondary consumer) → snake (tertiary) (lesson 2).

21BSEB model paper 2026 (not the annual exam) · Q80 · page 251 mark

Which of the following is a non-biodegradable substance?

  1. (A) DDT
  2. (B) Paper
  3. (C) Sewage
  4. (D) None of these
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Correct answer: (A) DDT

Pesticides like DDT are not broken by organisms — they collect in the food chain by biological magnification. Paper and sewage are biodegradable (lessons 3, 5).

22Book-based · 13.1 · ecosystem1 mark

Which of these is a human-made (artificial) ecosystem?

  1. (A) Forest
  2. (B) Pond
  3. (C) Crop-field
  4. (D) Lake
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Correct answer: (C) Crop-field

Forests, ponds and lakes are natural; gardens and crop-fields are human-made.

23Book-based · 13.1 · abiotic components1 mark

Which of these is an abiotic component of an ecosystem?

  1. (A) Bacteria
  2. (B) Temperature
  3. (C) Grass
  4. (D) Frog
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Correct answer: (B) Temperature

Temperature, rainfall, wind, soil and minerals are abiotic (non-living) components.

24Book-based · 13.1 · decomposers1 mark

Who breaks dead bodies into simple inorganic substances?

  1. (A) Producers
  2. (B) Herbivores
  3. (C) Decomposers
  4. (D) Carnivores
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Correct answer: (C) Decomposers

Bacteria and fungi = decomposers; they return matter to the soil.

25Book-based · 13.1 · consumers1 mark

Parasites belong to which group?

  1. (A) Producers
  2. (B) Consumers
  3. (C) Decomposers
  4. (D) Abiotic components
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Correct answer: (B) Consumers

The book divides consumers into herbivores, carnivores, omnivores and parasites.

26Book-based · 13.1.1 · first trophic level1 mark

Who are at the first trophic level of a food chain?

  1. (A) Herbivores
  2. (B) Producers
  3. (C) Decomposers
  4. (D) Large carnivores
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Correct answer: (B) Producers

Autotrophs (producers) are at the first level — they fix solar energy as food.

27Book-based · 13.1.1 · one percent1 mark

About how much of the sunlight falling on leaves do green plants convert into food?

  1. (A) 1%
  2. (B) 10%
  3. (C) 50%
  4. (D) 100%
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Correct answer: (A) 1%

About 1%. Then ~10% at each next level.

28Book-based · 13.1.1 · energy sum1 mark

Producers hold 10,000 J. By the ten percent law, how much reaches the secondary consumers?

  1. (A) 1000 J
  2. (B) 100 J
  3. (C) 10 J
  4. (D) 1 J
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Correct answer: (B) 100 J

10,000 → 1000 (primary) → 100 J (secondary).

29Book-based · 13.1.1 · length of a chain1 mark

Why do food chains usually have only 3–4 steps?

  1. (A) There are few organisms
  2. (B) Usable energy falls greatly at each level
  3. (C) Decomposers stop them
  4. (D) The Sun is far
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Correct answer: (B) Usable energy falls greatly at each level

About 90% of energy leaves at each level; after the fourth very little energy is left.

30Book-based · 13.1.1 · food web1 mark

A branching network of many linked food chains is called—

  1. (A) Trophic level
  2. (B) Food web
  3. (C) Ecosystem
  4. (D) Biological magnification
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Correct answer: (B) Food web

An organism is usually eaten by two or more kinds → a food web.

31Book-based · 13.1.1 · biological magnification1 mark

In biological magnification the harmful chemical is most concentrated in—

  1. (A) Producers
  2. (B) Herbivores
  3. (C) The top consumer (e.g. humans)
  4. (D) The soil
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Correct answer: (C) The top consumer (e.g. humans)

The chemical does not break down and builds up at each level — highest at the top.

32Book-based · 13.2.1 · ozone1 mark

How many oxygen atoms make one molecule of ozone?

  1. (A) 1
  2. (B) 2
  3. (C) 3
  4. (D) 4
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Correct answer: (C) 3

O₃ — three oxygen atoms.

33Book-based · 13.2.1 · ozone depletion1 mark

The main cause of depletion of the ozone layer is—

  1. (A) CO₂
  2. (B) Chlorofluorocarbons (CFCs)
  3. (C) Water vapour
  4. (D) Nitrogen
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Correct answer: (B) Chlorofluorocarbons (CFCs)

CFCs, used in refrigerators and fire extinguishers.

34Book-based · 13.2.2 · environment-friendly1 mark

For tea on a train, which cup is better for the environment?

  1. (A) Plastic cup
  2. (B) Paper cup
  3. (C) Polythene bag
  4. (D) Thermocol cup
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Correct answer: (B) Paper cup

Paper is biodegradable; plastic is not.

35Book-based · 13.2.2 · enzymes1 mark

Why is plastic not broken down by bacteria?

  1. (A) It is very heavy
  2. (B) Enzymes are specific
  3. (C) It dissolves in water
  4. (D) It is not green
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Correct answer: (B) Enzymes are specific

Each enzyme breaks one particular substance — that is why eating coal gives no energy, and plastic is not broken.

36NCERT exercise · Q21 mark

Which of the following constitute a food chain?

  1. (A) Grass, wheat and mango
  2. (B) Grass, goat and human
  3. (C) Goat, cow and elephant
  4. (D) Grass, fish and goat
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Correct answer: (B) Grass, goat and human

Grass → goat → human — producer, herbivore, then its eater. The other options do not form an eater–eaten order.

37NCERT exercise · Q31 mark

Which of the following are environment-friendly practices?

  1. (A) Carrying cloth-bags to put purchases in while shopping
  2. (B) Switching off unnecessary lights and fans
  3. (C) Walking to school instead of getting your mother to drop you on her scooter
  4. (D) All of the above
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Correct answer: (D) All of the above

All of the above — less plastic, saving electricity, saving fuel and avoiding pollution.

38Board-style (practice)1 mark

An abiotic component of an ecosystem is —

  1. (A) A frog
  2. (B) Soil
  3. (C) A fungus
  4. (D) Grass
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Correct answer: (B) Soil

Soil is abiotic. A frog, a fungus and grass are biotic.

39Board-style (practice)1 mark

A correct example of a food chain is —

  1. (A) Grass, goat, human
  2. (B) Mango, wheat, grass
  3. (C) Cow, goat, elephant
  4. (D) Fish, goat, grass
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Correct answer: (A) Grass, goat, human

Grass → goat → human is a chain.

40Board-style (practice)1 mark

The part of sunlight on the leaves that becomes food is about —

  1. (A) 1 percent
  2. (B) 10 percent
  3. (C) 50 percent
  4. (D) 90 percent
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Correct answer: (A) 1 percent

About 1 percent.

41Board-style (practice)1 mark

From 1000 J in the producers, the tertiary consumer receives —

  1. (A) 1000 J
  2. (B) 100 J
  3. (C) 10 J
  4. (D) 1 J
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Correct answer: (D) 1 J

1000 → 100 → 10 → 1 J. The tertiary consumer gets 1 J.

42Board-style (practice)1 mark

In biological magnification the highest concentration is in —

  1. (A) The producers
  2. (B) The water
  3. (C) The top consumer
  4. (D) Zero in the air
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Correct answer: (C) The top consumer

The amount is greatest in the top consumer.

43Board-style (practice)1 mark

Ozone near the ground —

  1. (A) Is the oxygen needed for breathing
  2. (B) Is a poison
  3. (C) Is only a food web
  4. (D) Is another name for CFC
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Correct answer: (B) Is a poison

Near the ground ozone is a poison. Up above it blocks UV.

44Board-style (practice)1 mark

The high ozone layer protects against —

  1. (A) Pesticides only
  2. (B) Ultraviolet rays
  3. (C) Sewage only
  4. (D) Plastic only
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Correct answer: (B) Ultraviolet rays

The layer protects against UV rays.

45Board-style (practice)1 mark

UNEP froze CFC production —

  1. (A) At the 1970 level
  2. (B) At the 1986 level
  3. (C) At the 2000 level
  4. (D) Not at all
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Correct answer: (B) At the 1986 level

In 1987 it was frozen at the 1986 level.

46Board-style (practice)1 mark

A non-biodegradable item is —

  1. (A) A vegetable peel
  2. (B) A plastic bag
  3. (C) Leftover cake
  4. (D) A used tea leaf
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Correct answer: (B) A plastic bag

A plastic bag is non-biodegradable.

47Board-style (practice)1 mark

When the waste is buried, the soil cover should be at least —

  1. (A) 1 cm
  2. (B) 15 cm
  3. (C) 15 m
  4. (D) Not 100 cm, only 1 mm
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Correct answer: (B) 15 cm

At least 15 cm of soil.

48Board-style (practice)1 mark

A paper cup is better than a plastic cup because —

  1. (A) Paper is biodegradable
  2. (B) Paper makes CFCs
  3. (C) Paper digs up fertile soil
  4. (D) Paper does not break down
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Correct answer: (A) Paper is biodegradable

Paper is biodegradable, so it is better than plastic.

49Board-style (practice)1 mark

Untreated sewage is harmful because —

  1. (A) It pollutes a water body
  2. (B) It makes ozone
  3. (C) It only increases producers
  4. (D) It is an aerator
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Correct answer: (A) It pollutes a water body

Untreated sewage pollutes local water.

50Board-style (practice)1 mark

E-waste can contain the hazard of —

  1. (A) Only pure water
  2. (B) Lead or mercury
  3. (C) Only grass
  4. (D) Only oxygen
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Correct answer: (B) Lead or mercury

Metals such as lead and mercury are hazardous.

51Board-style (practice)1 mark

If decomposers are removed —

  1. (A) Replenishment of the soil can stop
  2. (B) Sunlight will become 100 percent food
  3. (C) Ozone will only increase
  4. (D) The chain will start crossing like a line
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Correct answer: (A) Replenishment of the soil can stop

The soil will not receive the simple substances.

52BSEB model · practice (not an annual paper)1 mark

Which of the following is a natural ecosystem?

  1. (A) A crop-field
  2. (B) An aquarium
  3. (C) A lake
  4. (D) A garden
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Correct answer: (C) A lake

A lake is natural.

53BSEB model · practice (not an annual paper)1 mark

A secondary consumer is —

  1. (A) A producer
  2. (B) A herbivore
  3. (C) A small carnivore that eats a herbivore
  4. (D) Only a decomposer
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Correct answer: (C) A small carnivore that eats a herbivore

A small carnivore is a secondary consumer.

54Competency-based (not a PYQ)1 mark

A student puts into an aquarium a fish that eats the smaller fish. The most likely result is —

  1. (A) The chain will become longer and stable
  2. (B) One organism can eat the others and break the chain
  3. (C) 100 percent of the energy will return
  4. (D) Ozone will form
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Correct answer: (B) One organism can eat the others and break the chain

The predator fish can eat the others and break the chain.

55Competency-based (not a PYQ)1 mark

200000 J of sunlight falls on the leaves. Producers make food from 1 percent. The primary consumer receives —

  1. (A) 200000 J
  2. (B) 2000 J
  3. (C) 200 J
  4. (D) 20 J
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Correct answer: (C) 200 J

Food = 2000 J. The primary consumer gets 10 percent of that = 200 J.

← Chapter 13: Our Environment — full notes, video, questions