Class-12 Biology Ch-14 Ecosystem MCQs Exam 2027

Chapter: Ecosystem – Important MCQs

Topic 1: Structure and Components of Ecosystem

1. Who first proposed the term ‘Ecosystem’?

   (A) A.G. Tansley

   (B) E. Warming

   (C) E.P. Odum

   (D) G. Mendel

2. What are the two main components of an ecosystem?

   (A) Plants and animals

   (B) Weeds and trees

   (C) Biotic and Abiotic

   (D) Frog and Human

3. What kind of ecosystem is a lake?

   (A) Artificial

   (B) Abiotic

   (C) Natural

   (D) Waterless

4. What is the basic functional unit of the environment?

   (A) Species

   (B) Population

   (C) Community

   (D) Ecosystem

5. Which is the largest ecosystem on Earth?

   (A) Forest

   (B) Ocean

   (C) Grassland

   (D) Desert

6. Which of the following is NOT a producer?

   (A) Agaricus

   (B) Nostoc

   (C) Volvox

   (D) Spirogyra

7. In an ecosystem, green plants are called:

   (A) Producers

   (B) Consumers

   (C) Decomposers

   (D) None of these

8. Phytoplanktons are:

   (A) Autotrophs

   (B) Heterotrophs

   (C) Decomposers

   (D) None of these

9. In a grassland ecosystem, a grasshopper is a:

   (A) Producer

   (B) Primary consumer

   (C) Secondary consumer

   (D) Tertiary consumer

10. Tiger belongs to which category of consumer?

    (A) First order

    (B) Second order

    (C) Third order (Top Carnivore)

    (D) None of these

11. Which of the following is not a part of a forest ecosystem?

    (A) Lion

    (B) Grass

    (C) Algae

    (D) Deer

12. In a biotic community, primary consumers are always:

    (A) Carnivores

    (B) Detritivores

    (C) Herbivores

    (D) Omnivores

13. The second trophic level in a lake is:

    (A) Phytoplankton

    (B) Zooplankton

    (C) Fishes

    (D) Duck

14. What is the position of a Lion in a food chain?

    (A) Primary consumer

    (B) Secondary consumer

    (C) Top consumer

    (D) Producer

15. What do carnivorous animals represent?

    (A) Primary consumers

    (B) Secondary and Tertiary consumers

    (C) Only producers

    (D) Only herbivores

16. In an ecosystem, ‘Detritus’ means:

    (A) Dead organic matter

    (B) Living plants

    (C) Living animals

    (D) Rocks

17. Which is used for nitrogen fixation in soil?

    (A) Blue-green Algae

    (B) Protozoa

    (C) Nematodes

    (D) Wheat plants

18. The functional unit of an ecosystem is:

    (A) Ecosystem

    (B) Species

    (C) Population

    (D) Community

19. Temperature, Rainfall, and Soil are which type of components?

    (A) Biotic

    (B) Abiotic

    (C) Artificial

    (D) None of these

20. Who are the main producers in a pond ecosystem?

    (A) Fishes

    (B) Phytoplankton

    (C) Frogs

    (D) Zooplankton

Topic 2: Productivity and Decomposition

21. Conversion of solar energy into chemical energy is called:

    (A) Respiration

    (B) Photosynthesis

    (C) Transpiration

    (D) None of these

22. What is the correct formula for Net Primary Productivity (NPP)?

    (A) $NPP = GPP – R$

    (B) $NPP = GPP + R$

    (C) $NPP = GPP \times R$

    (D) $NPP = R / GPP$

23. Secondary productivity is related to:

    (A) Producer

    (B) Herbivore (Consumer)

    (C) Carnivore

    (D) None of these

24. Highest plant productivity is found in which biome?

    (A) Desert

    (B) Temperate Grassland

    (C) Tropical Rain Forest

    (D) Tundra

25. Decomposers are which type of organisms?

    (A) Autotrophs

    (B) Heterotrophs

    (C) Saprotrophs

    (D) Parasites

26. When is the rate of decomposition fast?

    (A) When the environment is cold

    (B) When there is a lack of oxygen

    (C) When moisture and warmth are adequate

    (D) When nitrogen is low

27. Fungi and Bacteria are called:

    (A) Producers

    (B) Consumers

    (C) Decomposers

    (D) Phytoplankton

28. What does ‘Leaching’ mean in the process of decomposition?

    (A) Movement of nutrients to lower soil layers

    (B) Breaking of leaves

    (C) Formation of humus

    (D) Release of minerals

29. What is the characteristic of Humus?

    (A) It is dark colored

    (B) It is colloidal in nature

    (C) It is rich in nutrients

    (D) All of the above

30. What happens if decomposers are removed from an ecosystem?

    (A) Energy flow will speed up

    (B) Mineral cycling will stop

    (C) Photosynthesis will increase

    (D) Population will increase

31. The raw material for decomposition is called:

    (A) Humus

    (B) Inorganic substance

    (C) Detritus

    (D) Sugar

32. How much PAR (Photosynthetically Active Radiation) is captured by plants?

    (A) 50%

    (B) 2-10%

    (C) 10%

    (D) 1%

33. In a grassland, the value of Gross Primary Productivity (GPP) is always:

    (A) Less than NPP

    (B) More than NPP

    (C) Equal to NPP

    (D) Zero

34. The process of soil formation is called:

    (A) Pedogenesis

    (B) Humification

    (C) Leaching

    (D) Catabolism

35. Organisms that obtain energy from dead organic matter are:

    (A) Saprotrophs

    (B) Autotrophs

    (C) Parasites

    (D) Carnivores

Topic 3: Energy Flow and Trophic Levels

36. Energy flow in any ecosystem is always:

    (A) Unidirectional

    (B) Bidirectional

    (C) Multidirectional

    (D) Cyclic

37. Who gave the 10% law of energy transfer?

    (A) Odum

    (B) Lindeman

    (C) Tansley

    (D) Darwin

38. What percentage of energy is transferred from one trophic level to the next?

    (A) 5%

    (B) 10%

    (C) 15%

    (D) 20%

39. The correct sequence of a simple food chain is:

    (A) Grass — Goat — Human

    (B) Goat — Grass — Human

    (C) Human — Goat — Grass

    (D) None of these

40. Where is maximum energy stored in a food chain?

    (A) Producer

    (B) Herbivore

    (C) Carnivore

    (D) Decomposer

41. How much energy is lost as heat when moving from one trophic level to another?

    (A) 10%

    (B) 90%

    (C) 50%

    (D) 1%

42. Herbivores occupy which level in a food chain?

    (A) First trophic level

    (B) Second trophic level

    (C) Third trophic level

    (D) Fourth trophic level

43. In a food chain, which group has the largest number (at the base)?

    (A) Producers

    (B) Primary consumers

    (C) Secondary consumers

    (D) Decomposers

44. If $CO_2$ is removed from the biosphere, who will be worst affected first?

    (A) Primary producers

    (B) Primary consumers

    (C) Secondary consumers

    (D) Decomposers

45. What does a Food Web represent?

    (A) Unidirectional flow of energy

    (B) Interrelationship and stability among organisms

    (C) Only the number of herbivores

    (D) None of these

46. Who is at the top of the energy pyramid?

    (A) Producer

    (B) Herbivore

    (C) Top Carnivore

    (D) Sun

47. Detritus Food Chain (DFC) begins with:

    (A) Living plants

    (B) Dead organic matter

    (C) Sunlight

    (D) Air

48. Small fishes in an aquatic chain are:

    (A) Primary consumers

    (B) Secondary consumers

    (C) Tertiary consumers

    (D) Producers

49. ‘Lindeman’s Rule’ of energy flow applies to:

    (A) Minerals

    (B) Respiration

    (C) Energy transfer between trophic levels

    (D) Population growth

50. In Grass → Grasshopper → Frog → Snake → Hawk; the trophic level of Snake is:

    (A) $T1$

    (B) $T2$

    (C) $T3$

    (D) $T4$

Topic 4: Ecological Pyramids

51. Which of the following pyramids can NEVER be inverted?

    (A) Pyramid of Number

    (B) Pyramid of Energy

    (C) Pyramid of Biomass

    (D) Pyramid of Size

52. The pyramid of biomass in a pond ecosystem is:

    (A) Upright

    (B) Inverted

    (C) Irregular

    (D) Linear

53. The pyramid of number in a forest ecosystem is generally:

    (A) Upright

    (B) Inverted

    (C) Crooked

    (D) None of these

54. The pyramid of energy in an aquatic ecosystem is always:

    (A) Always Upright

    (B) Always Inverted

    (C) Bell-shaped

    (D) Horizontal

55. The concept of ecological pyramids was first given by:

    (A) Charles Elton

    (B) Odum

    (C) Tansley

    (D) Mendel

56. In a tree ecosystem, the ‘pyramid of number’ will be (if many birds live on one tree):

    (A) Upright

    (B) Inverted

    (C) Rectangular

    (D) Circular

57. What does Biomass mean?

    (A) Dry weight of living organisms

    (B) Weight of animals only

    (C) Weight of plants only

    (D) Total water weight

58. The pyramid of number is based on:

    (A) Weight of organisms

    (B) Number of individuals

    (C) Amount of energy

    (D) Length of area

59. The pyramid of biomass in a grassland is:

    (A) Upright

    (B) Inverted

    (C) Irregular

    (D) None

60. At higher trophic levels, the amount of energy:

    (A) Increases

    (B) Decreases

    (C) Remains constant

    (D) Doubles

Topic 5: Ecological Succession

61. The first organism to inhabit an area during succession is called:

    (A) Climax species

    (B) Pioneer species

    (C) Intermediate species

    (D) Parasite

62. The pioneer species in a Hydrosere is:

    (A) Small floating plants

    (B) Rooted submerged plants

    (C) Phytoplankton

    (D) Marsh plants

63. Climax community is found in which area?

    (A) Balanced area

    (B) Transition area

    (C) Bare land

    (D) Only desert

64. The organisms that start succession on bare rocks are:

    (A) Fungi

    (B) Lichens

    (C) Algae

    (D) Ferns

65. The final stage in a hydrosere is:

    (A) Forest

    (B) Grassland

    (C) Phytoplankton

    (D) Marshy plants

66. Xerosere starts from:

    (A) Water

    (B) Dry or Bare area

    (C) Swamp

    (D) Ocean

67. The entire sequence of communities in succession is called:

    (A) Sere

    (B) Pyramid

    (C) Cycle

    (D) Stratification

68. Secondary succession occurs in:

    (A) Bare rock

    (B) Newly formed pond

    (C) Cut forests or abandoned farm lands

    (D) New lava

69. As compared to primary succession, the rate of secondary succession is:

    (A) Slower

    (B) Faster

    (C) Equal

    (D) Constant

70. In Lithosere, which organisms come after Lichens?

    (A) Trees

    (B) Mosses

    (C) Shrubs

    (D) Aquatic plants

71. The gradual development of plant species in an area is called:

    (A) Plant Succession

    (B) Photosynthesis

    (C) Mutation

    (D) Adaptation

72. What is the correct sequence of stages in a Hydrosere?

    (A) Phytoplankton → Submerged → Floating → Marsh → Forest

    (B) Forest → Marsh → Phytoplankton

    (C) Grass → Forest → Phytoplankton

    (D) None of these

73. The main function of a Pioneer community is:

    (A) To start soil formation

    (B) To provide shade

    (C) To soak water

    (D) To hunt

74. The nature of the Climax community depends on:

    (A) Soil

    (B) Local Climate

    (C) Number of organisms

    (D) None of these

75. Species that invade a bare area first are called:

    (A) Pioneer species

    (B) Seral species

    (C) Climax species

    (D) Parasite

Topic 6: Nutrient Cycling

76. The cycling of minerals in an ecosystem is called:

    (A) Geological cycle

    (B) Biogeochemical cycle

    (C) Chemical cycle

    (D) Water cycle

77. Which of the following is NOT a gaseous cycle?

    (A) Nitrogen cycle

    (B) Carbon cycle

    (C) Phosphorus cycle

    (D) Oxygen cycle

78. In the Phosphorus cycle, what is released first by weathering?

    (A) Phosphate ions

    (B) Nitrogen gas

    (C) Phosphoric acid

    (D) Calcium

79. What is the largest reservoir of nitrogen on Earth?

    (A) Soil

    (B) Atmosphere

    (C) Ocean

    (D) Rocks

80. The natural reservoir of phosphorus is:

    (A) Rocks

    (B) Atmosphere

    (C) Rivers

    (D) Rainwater

81. What is the main source of carbon in the carbon cycle?

    (A) Fossil fuels

    (B) Atmospheric $CO_2$ and Oceans

    (C) Soil

    (D) None of these

82. Biogeochemical cycle means:

    (A) Cycling of water

    (B) Cycling of nutrients in an ecosystem

    (C) Only flow of energy

    (D) Growth of plants

83. The percentage of $CO_2$ in the atmosphere is approximately:

    (A) 0.03%

    (B) 21%

    (C) 78%

    (D) 1%

84. An example of a Sedimentary Cycle is:

    (A) Carbon cycle

    (B) Phosphorus cycle

    (C) Nitrogen cycle

    (D) Hydrogen cycle

85. Which gas is released during respiration and contributes to the carbon cycle?

    (A) $O_2$

    (B) $CO_2$

    (C) $N_2$

    (D) $H_2$

86. Burning of fossil fuels directly affects which cycle?

    (A) Nitrogen cycle

    (B) Carbon cycle

    (C) Phosphorus cycle

    (D) Sulphur cycle

87. The movement of minerals from soil into plants is called:

    (A) Absorption

    (B) Transpiration

    (C) Respiration

    (D) None of these

88. Which cycle does not have a gaseous phase?

    (A) Phosphorus cycle

    (B) Water cycle

    (C) Nitrogen cycle

    (D) Carbon cycle

89. The role of bacteria in the Nitrogen cycle is in:

    (A) Fixation

    (B) Nitrification

    (C) Denitrification

    (D) All of the above

90. The stability of an ecosystem depends on:

    (A) Balance between nutrient cycling and energy flow

    (B) Rainfall only

    (C) Manuring only

    (D) Humans

Topic 7: Ecological Adaptation and Biodiversity

91. The Ozone layer protects from which rays?

    (A) Infra-red

    (B) Ultra-violet (UV)

    (C) X-ray

    (D) Gamma rays

92. Mycorrhiza is an example of:

    (A) Symbiosis

    (B) Parasitism

    (C) Saprophytism

    (D) Competition

93. Opuntia is an example of which type of adaptation?

    (A) Xerophytic

    (B) Hydrophytic

    (C) Halophytic

    (D) None of these

94. Lichen is a symbiotic relationship between:

    (A) Fungi and Algae

    (B) Fungi and Bacteria

    (C) Algae and Bacteria

    (D) Root and Fungi

95. Interaction between two species where both are benefited is:

    (A) Mutualism

    (B) Commensalism

    (C) Parasitism

    (D) Competition

96. Lichens are the best indicators of which pollution?

    (A) Water pollution

    (B) Air pollution ($SO_2$)

    (C) Noise pollution

    (D) Soil pollution

97. The main characteristic of Hydrophytes is:

    (A) Presence of Aerenchyma

    (B) Thick bark

    (C) Long roots

    (D) Spiny leaves

98. An example of Mutualism is:

    (A) Lichen

    (B) Mycorrhiza

    (C) Fig and Wasp

    (D) All of the above

99. In Commensalism:

    (A) One is benefited, other is unaffected

    (B) Both are benefited

    (C) Both are harmed

    (D) One is benefited, other is harmed

100. Cuscuta is an example of:

     (A) Total stem parasite

     (B) Partial root parasite

     (C) Commensalism

     (D) Producer

101. Diversity of species within a single area is called:

     (A) Alpha diversity

     (B) Beta diversity

     (C) Gamma diversity

     (D) Delta diversity

102. Eutrophication is observed in:

     (A) Deserts

     (B) Agricultural land

     (C) Lakes and Ponds

     (D) Mountains

103. Related to Genetic Engineering:

     (A) Missiles

     (B) Plasmids

     (C) Probe

     (D) Exon

104. Which is called “Lungs of the earth”?

     (A) Amazon Rain Forest

     (B) Himalayan Forests

     (C) Sahara Desert

     (D) Sundarbans

105. Which species became extinct due to over-exploitation?

     (A) Passenger Pigeon

     (B) Dodo bird

     (C) Steller’s Sea Cow

     (D) All of the above

106. How many mega-biodiversity countries are there in the world?

     (A) 12

     (B) 17

     (C) 25

     (D) 100

107. The best way to measure population density is:

     (A) Number

     (B) Biomass

     (C) Percent cover

     (D) All of the above

108. Ratio of mortality and natality is called:

     (A) Vital Index

     (B) Density

     (C) Age pyramid

     (D) None

109. Pollination in Ophrys orchid occurs by:

     (A) Pseudocopulation by bees/wasps

     (B) Air

     (C) Water

     (D) Self

110. In Grass → Goat → Human, what is the human?

     (A) Primary consumer

     (B) Secondary consumer

     (C) Producer

     (D) Decomposer

111. Main loss of energy in an ecosystem is in the form of:

     (A) Food

     (B) Heat

     (C) Water

     (D) Excreta

112. Which is grown under ‘Silviculture’?

     (A) Fish

     (B) Forest trees

     (C) Crops

     (D) Silkworm

113. Who is considered the father of Ecology?

     (A) Reiter / Ramdeo Misra (in India)

     (B) Darwin

     (C) Mendel

     (D) Aristotle

114. Requirement for a biodiversity hotspot is:

     (A) High Endemism

     (B) Species richness

     (C) High level of threat

     (D) All of the above

115. Which is the national aquatic animal of India?

     (A) Blue Whale

     (B) Seahorse

     (C) Gangetic Dolphin

     (D) Turtle

116. Kanha National Park is famous for:

     (A) Lion

     (B) Tiger

     (C) Rhino

     (D) Crocodile

117. Chipko Movement is related to:

     (A) Conservation of trees

     (B) Tigers

     (C) Rivers

     (D) Minerals

118. When is World Environment Day celebrated?

     (A) June 5

     (B) December 1

     (C) April 22

     (D) September 16

119. The main cause of Ozone hole is:

     (A) $CO_2$

     (B) CFC (Chlorofluorocarbon)

     (C) $CH_4$

     (D) $N_2O$

120. Main greenhouse gas responsible for global warming is:

     (A) $CO_2$

     (B) $O_2$

     (C) $N_2$

     (D) $CO$

121. Ranthambore National Park is located in:

     (A) Bihar

     (B) Uttar Pradesh

     (C) Rajasthan

     (D) Gujarat

122. Kaziranga is famous for:

     (A) One-horned Rhino

     (B) Elephant

     (C) Birds

     (D) Lion

123. Sacred Groves are found in:

     (A) Khasi and Jaintia hills

     (B) Western Ghats

     (C) Aravalli ranges

     (D) All of the above

124. Who publishes the Red Data Book?

     (A) IUCN

     (B) WHO

     (C) UNESCO

     (D) WWF

125. An example of In-situ conservation is:

     (A) Zoo

     (B) National Park

     (C) Botanical Garden

     (D) Seed Bank

126. An example of Ex-situ conservation is:

     (A) Wildlife Sanctuary

     (B) Biosphere Reserve

     (C) Zoological Park

     (D) Sacred Lakes

127. The largest food chain in the world is:

     (A) Grassland

     (B) Forest

     (C) Marine (Ocean)

     (D) Desert

128. Total number of species found in an area represents:

     (A) Species Richness

     (B) Species Evenness

     (C) Population Density

     (D) None of these

129. Which group has the most species in the Amazon rain forest?

     (A) Mammals

     (B) Birds

     (C) Fishes

     (D) Insects

130. Who coined the term ‘Hotspot’?

     (A) Norman Myers

     (B) Edward Wilson

     (C) Ramdeo Misra

     (D) Odum

131. How many biodiversity hotspots are in India?

     (A) 2

     (B) 3

     (C) 4

     (D) 10

132. The cyclic path of elements in an ecosystem is called:

     (A) Biogeochemical cycle

     (B) Biotic cycle

     (C) Ecological cycle

     (D) Chemical path

133. The study of an individual species in relation to its environment is:

     (A) Autecology

     (B) Synecology

     (C) Phytogeography

     (D) None

134. Inverted pyramid of biomass can be found in:

     (A) Pond

     (B) Ocean

     (C) Both (A) and (B)

     (D) Grassland

135. What is continuously required in an ecosystem?

     (A) Input of Energy (Sunlight)

     (B) Only water

     (C) Only soil

     (D) None of these