Chapter 15 – Our Environment – MCQs
Chapter 15 – Our Environment – MCQs (Part 1: Q1–Q25)
Q1. Which of the following is a biodegradable substance?
a) Plastic
b) Glass
c) Paper
d) Aluminium foil
✅ Answer: c) Paper
Explanation: Paper is biodegradable as it can be decomposed by microorganisms.
Q2. Which of the following is a non-biodegradable waste?
a) Vegetable peels
b) Cotton cloth
c) Plastic bottles
d) Wood
✅ Answer: c) Plastic bottles
Explanation: Plastics are synthetic polymers that do not decompose naturally.
Q3. Which of the following organisms form the first trophic level in a food chain?
a) Herbivores
b) Producers
c) Carnivores
d) Omnivores
✅ Answer: b) Producers
Explanation: Producers like green plants prepare food through photosynthesis, forming the first trophic level.
Q4. The 10% law of energy transfer in a food chain was given by:
a) Mendel
b) Darwin
c) Lindeman
d) Watson
✅ Answer: c) Lindeman
Explanation: Lindeman proposed that only 10% of energy is transferred from one trophic level to the next.
Q5. Which of the following is an example of a primary consumer?
a) Lion
b) Deer
c) Grass
d) Tiger
✅ Answer: b) Deer
Explanation: Deer eats plants (producers) and is a herbivore, hence a primary consumer.
Q6. In a food chain, the flow of energy is:
a) Unidirectional
b) Bidirectional
c) Circular
d) Reversible
✅ Answer: a) Unidirectional
Explanation: Energy flows from producers to consumers and is lost as heat, it cannot be reversed.
Q7. The largest reservoir of carbon dioxide on Earth is:
a) Forests
b) Oceans
c) Soil
d) Fossil fuels
✅ Answer: b) Oceans
Explanation: Oceans store the largest amount of CO₂ as dissolved carbonates and bicarbonates.
Q8. Which of the following is NOT a greenhouse gas?
a) Carbon dioxide
b) Methane
c) Nitrous oxide
d) Oxygen
✅ Answer: d) Oxygen
Explanation: Oxygen is not a greenhouse gas; it does not trap heat in the atmosphere.
Q9. Ozone depletion is mainly caused by:
a) CFCs
b) CO₂
c) CH₄
d) SO₂
✅ Answer: a) CFCs
Explanation: Chlorofluorocarbons (CFCs) release chlorine atoms that destroy ozone molecules.
Q10. Which of the following is the correct sequence of a food chain?
a) Carnivore → Producer → Herbivore
b) Producer → Herbivore → Carnivore
c) Herbivore → Producer → Carnivore
d) Producer → Carnivore → Herbivore
✅ Answer: b) Producer → Herbivore → Carnivore
Explanation: Plants (producers) are eaten by herbivores, which are eaten by carnivores.
Q11. Which of the following is an abiotic component of the ecosystem?
a) Plants
b) Animals
c) Bacteria
d) Water
✅ Answer: d) Water
Explanation: Abiotic components are non-living factors like water, air, and soil.
Q12. Which of the following is a secondary consumer?
a) Grasshopper
b) Cow
c) Frog
d) Grass
✅ Answer: c) Frog
Explanation: Frog eats insects (primary consumers) and hence is a secondary consumer.
Q13. Which of the following contributes to biomagnification?
a) Water
b) Pesticides
c) Sunlight
d) Oxygen
✅ Answer: b) Pesticides
Explanation: Harmful chemicals like DDT accumulate in organisms at higher trophic levels.
Q14. The main reason for the accumulation of pesticides in the food chain is:
a) They are biodegradable
b) They are non-biodegradable
c) They are soluble in water
d) They are used in small amounts
✅ Answer: b) They are non-biodegradable
Explanation: Non-biodegradable pesticides persist in the environment and accumulate in organisms.
Q15. Which of the following is an example of an omnivore?
a) Cow
b) Lion
c) Human
d) Goat
✅ Answer: c) Human
Explanation: Humans eat both plants and animals, making them omnivores.
Q16. Which of the following forms the last trophic level in a food chain?
a) Producers
b) Herbivores
c) Decomposers
d) Carnivores
✅ Answer: d) Carnivores
Explanation: Carnivores occupy the top trophic levels in a food chain. Decomposers act separately.
Q17. Which one of the following gases is released during photosynthesis?
a) Carbon dioxide
b) Oxygen
c) Nitrogen
d) Methane
✅ Answer: b) Oxygen
Explanation: During photosynthesis, plants take in CO₂ and release O₂.
Q18. Which of the following is a natural decomposer?
a) Fungus
b) Rabbit
c) Lion
d) Deer
✅ Answer: a) Fungus
Explanation: Fungi break down dead organic matter, recycling nutrients into the ecosystem.
Q19. Which of the following is an effect of global warming?
a) Melting of glaciers
b) Decrease in sea level
c) Increase in ozone layer
d) More forest cover
✅ Answer: a) Melting of glaciers
Explanation: Global warming increases temperature, leading to ice melting and sea-level rise.
Q20. Which of the following organisms are called autotrophs?
a) Animals
b) Green plants
c) Humans
d) Fungi
✅ Answer: b) Green plants
Explanation: Green plants prepare their own food through photosynthesis and are autotrophs.
Q21. Which of the following is a renewable resource?
a) Petroleum
b) Coal
c) Forests
d) Natural gas
✅ Answer: c) Forests
Explanation: Forests can regenerate naturally if managed properly, making them renewable.
Q22. Which of the following leads to ozone layer depletion?
a) Oxygen
b) Nitrogen
c) CFCs
d) Carbon monoxide
✅ Answer: c) CFCs
Explanation: Chlorofluorocarbons break down ozone molecules in the stratosphere.
Q23. Which of the following is the ultimate source of energy in an ecosystem?
a) Wind
b) Water
c) Sun
d) Fossil fuels
✅ Answer: c) Sun
Explanation: The sun provides energy for photosynthesis, supporting all life forms.
Q24. Which of the following is NOT a part of the biotic component of the ecosystem?
a) Plants
b) Animals
c) Microorganisms
d) Soil
✅ Answer: d) Soil
Explanation: Soil is non-living and thus an abiotic component.
Q25. Which of the following is an example of a decomposer in the ecosystem?
a) Cow
b) Human
c) Bacteria
d) Grass
✅ Answer: c) Bacteria
Explanation: Bacteria decompose dead organic matter and recycle nutrients in the ecosystem.
Our Environment – MCQs (Part 2: Q26–Q50)
Q26. The main constituent of the ozone layer is:
a) O₂
b) O₃
c) CO₂
d) N₂
✅ Answer: b) O₃
Explanation: Ozone (O₃) is a triatomic form of oxygen that absorbs harmful UV rays.
Q27. Which of the following is NOT an example of a primary consumer?
a) Cow
b) Goat
c) Grasshopper
d) Lion
✅ Answer: d) Lion
Explanation: Lion is a carnivore and occupies the tertiary consumer level, not the primary level.
Q28. Which of the following is the correct term for all the interconnected food chains in an ecosystem?
a) Food link
b) Food cycle
c) Food web
d) Food pyramid
✅ Answer: c) Food web
Explanation: A food web is a network of interconnected food chains in an ecosystem.
Q29. Which of the following pollutants causes “smog” in cities?
a) Oxygen
b) Carbon monoxide
c) Nitrogen oxides
d) Ozone
✅ Answer: c) Nitrogen oxides
Explanation: Nitrogen oxides combine with hydrocarbons to form photochemical smog.
Q30. Which of the following is a non-renewable resource?
a) Solar energy
b) Wind energy
c) Petroleum
d) Forests
✅ Answer: c) Petroleum
Explanation: Petroleum reserves are limited and cannot be replenished once exhausted.
Q31. Which of the following is a major cause of acid rain?
a) Oxygen
b) Sulphur dioxide
c) Nitrogen gas
d) Hydrogen
✅ Answer: b) Sulphur dioxide
Explanation: SO₂ and NOx react with water vapour to form acids, causing acid rain.
Q32. The flow of materials in an ecosystem is:
a) Cyclic
b) Unidirectional
c) Bidirectional
d) Random
✅ Answer: a) Cyclic
Explanation: Nutrients like carbon, nitrogen, and water cycle through the ecosystem.
Q33. Which of the following is the best method to reduce non-biodegradable waste?
a) Burning
b) Dumping
c) Recycling
d) Burying
✅ Answer: c) Recycling
Explanation: Recycling helps reuse non-biodegradable materials like plastic and glass.
Q34. Which of the following is the most harmful to aquatic life due to eutrophication?
a) Excess oxygen
b) Excess carbon dioxide
c) Excess nutrients (fertilizers)
d) Excess sunlight
✅ Answer: c) Excess nutrients (fertilizers)
Explanation: Runoff containing fertilizers causes algae bloom, reducing oxygen in water.
Q35. Which of the following is NOT a renewable source of energy?
a) Coal
b) Sunlight
c) Wind
d) Water
✅ Answer: a) Coal
Explanation: Coal is a fossil fuel and non-renewable.
Q36. Which of the following correctly represents the 10% law?
a) Producers → 1000J, Herbivores → 100J
b) Producers → 100J, Herbivores → 1000J
c) Producers → 1000J, Herbivores → 500J
d) Producers → 1000J, Herbivores → 900J
✅ Answer: a) Producers → 1000J, Herbivores → 100J
Explanation: Only 10% of energy passes to the next trophic level; rest is lost as heat.
Q37. Which of the following is NOT biodegradable?
a) Vegetable waste
b) Paper
c) Polythene
d) Cotton cloth
✅ Answer: c) Polythene
Explanation: Polythene is non-biodegradable and persists in the environment.
Q38. Which of the following is an abiotic factor in an ecosystem?
a) Sunlight
b) Plants
c) Animals
d) Decomposers
✅ Answer: a) Sunlight
Explanation: Sunlight is a non-living (abiotic) factor that supports life.
Q39. Which of the following is responsible for the greenhouse effect?
a) Oxygen
b) Nitrogen
c) Carbon dioxide
d) Argon
✅ Answer: c) Carbon dioxide
Explanation: CO₂ traps heat, leading to global warming.
Q40. Which of the following shows the correct food chain?
a) Grass → Cow → Human
b) Grass → Human → Cow
c) Cow → Grass → Human
d) Human → Grass → Cow
✅ Answer: a) Grass → Cow → Human
Explanation: Grass (producer) → Cow (herbivore) → Human (omnivore).
Q41. Which of the following is an artificial ecosystem?
a) Forest
b) Lake
c) Aquarium
d) Pond
✅ Answer: c) Aquarium
Explanation: Aquarium is a man-made ecosystem maintained by humans.
Q42. Which of the following is NOT a consequence of ozone layer depletion?
a) Skin cancer
b) Eye cataracts
c) Enhanced UV radiation
d) Reduced greenhouse gases
✅ Answer: d) Reduced greenhouse gases
Explanation: Ozone depletion does not affect greenhouse gases.
Q43. Which of the following statements about food chains is correct?
a) Energy transfer is 100% efficient
b) Energy flow is unidirectional
c) Consumers produce their own food
d) Decomposers occupy the first trophic level
✅ Answer: b) Energy flow is unidirectional
Explanation: Energy flows in one direction, from producers to consumers.
Q44. Which of the following is a secondary consumer in a pond ecosystem?
a) Algae
b) Fish
c) Zooplankton
d) Insects
✅ Answer: b) Fish
Explanation: Fish eat zooplankton (primary consumers), so they are secondary consumers.
Q45. Which of the following is a gaseous cycle?
a) Carbon cycle
b) Nitrogen cycle
c) Oxygen cycle
d) All of these
✅ Answer: d) All of these
Explanation: All involve circulation of gases between organisms and the atmosphere.
Q46. The most stable ecosystem is:
a) Forest
b) Desert
c) Lake
d) Grassland
✅ Answer: a) Forest
Explanation: Forests are highly self-sustaining, biodiverse, and stable ecosystems.
Q47. Which of the following is NOT a function of decomposers?
a) Recycling nutrients
b) Producing energy directly from sunlight
c) Breaking down organic matter
d) Returning nutrients to soil
✅ Answer: b) Producing energy directly from sunlight
Explanation: Only producers make energy from sunlight, not decomposers.
Q48. Which of the following is a natural method of waste disposal?
a) Composting
b) Incineration
c) Landfilling
d) Plastic burning
✅ Answer: a) Composting
Explanation: Composting decomposes biodegradable waste naturally into manure.
Q49. Which of the following correctly represents a pyramid of biomass?
a) Producer biomass is highest
b) Herbivore biomass is highest
c) Carnivore biomass is highest
d) All levels have equal biomass
✅ Answer: a) Producer biomass is highest
Explanation: Producers have the maximum biomass, supporting higher levels.
Q50. Which of the following is NOT a renewable energy source?
a) Wind energy
b) Solar energy
c) Geothermal energy
d) Natural gas
✅ Answer: d) Natural gas
Explanation: Natural gas is a fossil fuel and non-renewable.
Our Environment – MCQs (Part 3: Q51–Q75)
Q51. Which of the following is the primary source of energy in all ecosystems?
a) Water
b) Sun
c) Wind
d) Soil
✅ Answer: b) Sun
Explanation: The sun provides energy to producers through photosynthesis, forming the base of all ecosystems.
Q52. Which of the following best explains “biological magnification”?
a) Increase in biomass at higher trophic levels
b) Decrease in energy at higher trophic levels
c) Accumulation of harmful substances at each trophic level
d) Loss of heat at each trophic level
✅ Answer: c) Accumulation of harmful substances at each trophic level
Explanation: Non-biodegradable chemicals like DDT accumulate in organisms, increasing at higher levels.
Q53. Which of the following is an example of a decomposer?
a) Grass
b) Lion
c) Mushroom
d) Goat
✅ Answer: c) Mushroom
Explanation: Mushrooms are fungi that decompose dead organic matter.
Q54. Which of the following is NOT a harmful effect of plastic waste?
a) Choking of drains
b) Killing of animals
c) Increasing soil fertility
d) Air pollution when burnt
✅ Answer: c) Increasing soil fertility
Explanation: Plastics harm soil; they do not improve fertility.
Q55. Which of the following forms the base of the ecological pyramid?
a) Herbivores
b) Producers
c) Carnivores
d) Omnivores
✅ Answer: b) Producers
Explanation: Producers form the first trophic level and provide energy to all higher levels.
Q56. Which of the following statements about decomposers is true?
a) They form food by photosynthesis
b) They recycle nutrients back into the soil
c) They occupy the first trophic level
d) They are secondary consumers
✅ Answer: b) They recycle nutrients back into the soil
Explanation: Decomposers convert dead matter into simple substances that return to soil.
Q57. Which of the following ecosystems is the most productive?
a) Desert
b) Ocean
c) Forest
d) Grassland
✅ Answer: c) Forest
Explanation: Forests have high biodiversity and biomass, making them highly productive.
Q58. Which of the following is the correct sequence of a grassland food chain?
a) Grass → Grasshopper → Frog → Snake → Hawk
b) Snake → Frog → Grasshopper → Grass → Hawk
c) Hawk → Snake → Frog → Grasshopper → Grass
d) Grasshopper → Grass → Snake → Frog → Hawk
✅ Answer: a) Grass → Grasshopper → Frog → Snake → Hawk
Explanation: Producers → Herbivores → Secondary consumers → Tertiary consumers → Top carnivores.
Q59. Which of the following is NOT a greenhouse gas?
a) Carbon dioxide
b) Methane
c) Oxygen
d) Nitrous oxide
✅ Answer: c) Oxygen
Explanation: Oxygen does not trap heat, so it is not a greenhouse gas.
Q60. Which of the following organisms is at the second trophic level in a food chain?
a) Plants
b) Herbivores
c) Carnivores
d) Decomposers
✅ Answer: b) Herbivores
Explanation: Herbivores feed on producers and form the second trophic level.
Q61. Which of the following cycles is NOT a biogeochemical cycle?
a) Nitrogen cycle
b) Carbon cycle
c) Oxygen cycle
d) Energy cycle
✅ Answer: d) Energy cycle
Explanation: Energy flows unidirectionally, not cyclically, hence not a cycle.
Q62. Which of the following increases the risk of skin cancer in humans?
a) Ozone layer depletion
b) Carbon monoxide
c) Greenhouse effect
d) Acid rain
✅ Answer: a) Ozone layer depletion
Explanation: Ozone depletion allows more UV rays to reach Earth, causing skin cancer.
Q63. Which of the following is NOT an example of an ecosystem?
a) Pond
b) Aquarium
c) Forest
d) Plastic bottle
✅ Answer: d) Plastic bottle
Explanation: An ecosystem must have both living and non-living interactions; plastic is non-living only.
Q64. Which of the following describes “eutrophication”?
a) Oxygen increase in water bodies
b) Excess nutrient enrichment of water bodies
c) Decrease in fish population
d) Melting of ice caps
✅ Answer: b) Excess nutrient enrichment of water bodies
Explanation: Eutrophication is caused by nutrient runoff leading to algal blooms.
Q65. Which of the following is the apex predator in a terrestrial food chain?
a) Deer
b) Tiger
c) Rabbit
d) Grass
✅ Answer: b) Tiger
Explanation: Tiger is a top carnivore at the last trophic level in the food chain.
Q66. Which of the following wastes takes the longest time to decompose?
a) Vegetable peels
b) Paper
c) Polythene bag
d) Cotton cloth
✅ Answer: c) Polythene bag
Explanation: Polythene is non-biodegradable and persists in the environment for centuries.
Q67. Which of the following is a harmful effect of eutrophication?
a) Increase in oxygen levels
b) Decrease in aquatic life
c) Increase in fish diversity
d) Increase in water clarity
✅ Answer: b) Decrease in aquatic life
Explanation: Algal blooms reduce oxygen levels, suffocating aquatic life.
Q68. Which of the following is the best way to reduce plastic waste?
a) Burning plastic
b) Using cloth bags
c) Burying plastic
d) Dumping plastic in water
✅ Answer: b) Using cloth bags
Explanation: Cloth bags reduce plastic use and are eco-friendly.
Q69. Which of the following is NOT a renewable energy resource?
a) Wind
b) Solar
c) Geothermal
d) Coal
✅ Answer: d) Coal
Explanation: Coal is non-renewable and exhaustible.
Q70. Which of the following represents a detritus food chain?
a) Grass → Cow → Human
b) Dead leaves → Earthworm → Bird
c) Grass → Rabbit → Tiger
d) Phytoplankton → Zooplankton → Fish
✅ Answer: b) Dead leaves → Earthworm → Bird
Explanation: Detritus food chain starts with decomposing organic matter.
Q71. Which of the following is a harmful effect of global warming?
a) Rise in sea levels
b) Increase in biodiversity
c) Stable climate
d) More crop productivity everywhere
✅ Answer: a) Rise in sea levels
Explanation: Global warming melts glaciers, raising sea levels and flooding areas.
Q72. Which of the following organisms is a tertiary consumer?
a) Grasshopper
b) Frog
c) Snake
d) Eagle
✅ Answer: d) Eagle
Explanation: Eagle eats snakes and other carnivores, making it a tertiary consumer.
Q73. Which of the following is the ultimate fate of energy in ecosystems?
a) Recycled by decomposers
b) Lost as heat
c) Stored in fossil fuels
d) Stored permanently in soil
✅ Answer: b) Lost as heat
Explanation: Energy is eventually lost as heat during metabolic processes.
Q74. Which of the following cycles does NOT involve atmosphere?
a) Water cycle
b) Carbon cycle
c) Phosphorus cycle
d) Nitrogen cycle
✅ Answer: c) Phosphorus cycle
Explanation: The phosphorus cycle occurs mostly in rocks, soil, and water, not atmosphere.
Q75. Which of the following is the most environment-friendly method of waste disposal?
a) Open dumping
b) Incineration
c) Composting
d) Landfilling
✅ Answer: c) Composting
Explanation: Composting converts biodegradable waste into useful manure naturally.
Our Environment – MCQs (Part 4: Q76–Q100)
Q76. Which of the following is a primary consumer in a pond ecosystem?
a) Algae
b) Zooplankton
c) Fish
d) Frog
✅ Answer: b) Zooplankton
Explanation: Zooplankton feed on algae (producers) and are primary consumers.
Q77. Which of the following is the most eco-friendly fuel?
a) Coal
b) Petrol
c) Diesel
d) CNG
✅ Answer: d) CNG
Explanation: Compressed Natural Gas (CNG) burns cleanly with fewer pollutants.
Q78. Which of the following is NOT a harmful effect of deforestation?
a) Loss of biodiversity
b) Soil erosion
c) Desertification
d) Increase in groundwater
✅ Answer: d) Increase in groundwater
Explanation: Deforestation reduces groundwater recharge instead of increasing it.
Q79. Which of the following is an example of a tertiary consumer?
a) Grasshopper
b) Frog
c) Snake
d) Tiger
✅ Answer: d) Tiger
Explanation: Tiger feeds on herbivores and carnivores, making it a tertiary consumer.
Q80. Which of the following is the main cause of ozone layer depletion?
a) CO₂
b) SO₂
c) CFCs
d) NO₂
✅ Answer: c) CFCs
Explanation: Chlorofluorocarbons release chlorine radicals that destroy ozone.
Q81. Which of the following organisms is a decomposer?
a) Caterpillar
b) Vulture
c) Bacteria
d) Snake
✅ Answer: c) Bacteria
Explanation: Bacteria decompose organic matter and recycle nutrients.
Q82. Which of the following is the main cause of acid rain?
a) CO₂
b) SO₂ and NOx
c) O₃
d) CH₄
✅ Answer: b) SO₂ and NOx
Explanation: Sulphur dioxide and nitrogen oxides form acids in the atmosphere, causing acid rain.
Q83. Which of the following is NOT a greenhouse gas?
a) CO₂
b) CH₄
c) N₂O
d) O₂
✅ Answer: d) O₂
Explanation: Oxygen is not a greenhouse gas.
Q84. Which of the following is the most stable ecosystem?
a) Desert
b) Grassland
c) Ocean
d) Forest
✅ Answer: c) Ocean
Explanation: Oceans are large, self-sustaining, and least affected by human activity compared to others.
Q85. Which of the following is a disadvantage of using pesticides?
a) They increase crop yield
b) They cause biomagnification
c) They kill harmful insects
d) They protect crops
✅ Answer: b) They cause biomagnification
Explanation: Non-biodegradable pesticides accumulate in organisms, harming ecosystems.
Q86. Which of the following is the best way to manage biodegradable waste?
a) Composting
b) Burning
c) Landfilling
d) Dumping in water
✅ Answer: a) Composting
Explanation: Composting converts biodegradable waste into manure naturally.
Q87. Which of the following forms the first trophic level in an ecosystem?
a) Herbivores
b) Producers
c) Carnivores
d) Decomposers
✅ Answer: b) Producers
Explanation: Producers like plants form the base of the food chain.
Q88. Which of the following shows the correct food chain in a forest ecosystem?
a) Grass → Deer → Lion
b) Lion → Deer → Grass
c) Deer → Grass → Lion
d) Grass → Lion → Deer
✅ Answer: a) Grass → Deer → Lion
Explanation: Producers → Herbivores → Carnivores.
Q89. Which of the following is an abiotic factor in an ecosystem?
a) Plants
b) Animals
c) Soil
d) Bacteria
✅ Answer: c) Soil
Explanation: Soil is non-living, so it is abiotic.
Q90. Which of the following is NOT biodegradable?
a) Cotton cloth
b) Vegetable waste
c) Glass bottle
d) Paper
✅ Answer: c) Glass bottle
Explanation: Glass does not decompose naturally.
Q91. Which of the following is the ultimate source of energy in a food chain?
a) Water
b) Wind
c) Sun
d) Soil
✅ Answer: c) Sun
Explanation: Solar energy drives photosynthesis, supporting the food chain.
Q92. Which of the following is an example of an artificial ecosystem?
a) Pond
b) Forest
c) Aquarium
d) Lake
✅ Answer: c) Aquarium
Explanation: Aquarium is man-made and maintained artificially.
Q93. Which of the following is responsible for global warming?
a) Oxygen
b) Nitrogen
c) Carbon dioxide
d) Helium
✅ Answer: c) Carbon dioxide
Explanation: CO₂ traps heat, increasing Earth’s temperature.
Q94. Which of the following is NOT an advantage of recycling?
a) Conserves resources
b) Reduces pollution
c) Increases waste
d) Saves energy
✅ Answer: c) Increases waste
Explanation: Recycling reduces waste, it does not increase it.
Q95. Which of the following is an example of a detritivore?
a) Earthworm
b) Cow
c) Deer
d) Lion
✅ Answer: a) Earthworm
Explanation: Earthworms feed on decomposing organic matter.
Q96. Which of the following is the correct order of a marine food chain?
a) Phytoplankton → Zooplankton → Fish → Seal
b) Fish → Zooplankton → Phytoplankton → Seal
c) Seal → Fish → Zooplankton → Phytoplankton
d) Zooplankton → Fish → Seal → Phytoplankton
✅ Answer: a) Phytoplankton → Zooplankton → Fish → Seal
Explanation: Producers → Primary consumers → Secondary consumers → Tertiary consumers.
Q97. Which of the following is the correct statement about energy flow in ecosystems?
a) Energy is recycled
b) Energy flow is cyclic
c) Energy flow is unidirectional
d) Energy remains constant
✅ Answer: c) Energy flow is unidirectional
Explanation: Energy flows one way, from producers to consumers, and is lost as heat.
Q98. Which of the following is an example of biomagnification?
a) Increase in oxygen
b) Accumulation of DDT in food chain
c) Recycling of waste
d) Photosynthesis
✅ Answer: b) Accumulation of DDT in food chain
Explanation: Pesticides like DDT accumulate in organisms, magnifying at higher levels.
Q99. Which of the following correctly represents a pyramid of numbers in a forest?
a) Many producers → Few herbivores → Fewer carnivores
b) Few producers → Many herbivores → Many carnivores
c) Equal producers and herbivores
d) Many carnivores → Few producers
✅ Answer: a) Many producers → Few herbivores → Fewer carnivores
Explanation: Forest ecosystems have many trees, fewer herbivores, and even fewer carnivores.
Q100. Which of the following is the most environment-friendly habit?
a) Using plastic bags
b) Throwing garbage in open
c) Segregating waste and composting
d) Burning polythene
✅ Answer: c) Segregating waste and composting
Explanation: Segregation and composting reduce pollution and recycle biodegradable waste.
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