🌱 Ecosystem MCQs (Part 1: Q1–Q25)

Q1. The functional unit of ecology is:

a) Community
b) Ecosystem ✅
c) Population
d) Species

Explanation: An ecosystem includes both biotic and abiotic components and their interactions, making it the basic functional unit of ecology.

Q2. In an ecosystem, producers are:

a) Herbivores
b) Carnivores
c) Green plants ✅
d) Decomposers

Explanation: Producers are autotrophs, mainly green plants and algae, that capture solar energy to make food via photosynthesis.

Q3. Which of the following is a detritivore?

a) Cow
b) Earthworm ✅
c) Lion
d) Grasshopper

Explanation: Earthworms feed on dead and decaying matter, making them detritivores.

Q4. Which ecosystem has the highest productivity?

a) Desert
b) Tundra
c) Tropical rainforest ✅
d) Grassland

Explanation: Tropical rainforests have high temperature, moisture, and biodiversity, resulting in the highest productivity.

Q5. Energy flow in an ecosystem is always:

a) Cyclic
b) Linear ✅
c) Random
d) Reversible

Explanation: Energy flows in one direction, from producers to consumers, and cannot be reused once lost as heat.

Q6. Which pyramid is always upright?

a) Pyramid of energy ✅
b) Pyramid of number
c) Pyramid of biomass
d) Both b and c

Explanation: Energy decreases at successive trophic levels due to the second law of thermodynamics, so energy pyramids are always upright.

Q7. Secondary consumers in a grassland ecosystem are:

a) Grass
b) Grasshopper
c) Frog ✅
d) Lion

Explanation: Frogs feed on herbivorous insects like grasshoppers, making them secondary consumers.

Q8. The ultimate source of energy for all ecosystems is:

a) Water
b) Soil
c) Sun ✅
d) Green plants

Explanation: The sun provides energy that drives photosynthesis, forming the base of all ecosystems.

Q9. Which nutrient cycle is a gaseous cycle?

a) Phosphorus cycle
b) Sulphur cycle
c) Nitrogen cycle ✅
d) Calcium cycle

Explanation: Nitrogen cycle involves atmospheric nitrogen and is a gaseous cycle.

Q10. Decomposers are also known as:

a) Saprotrophs ✅
b) Autotrophs
c) Herbivores
d) Carnivores

Explanation: Decomposers (fungi, bacteria) feed on dead matter through external digestion, hence called saprotrophs.

Q11. Which one of the following is a pioneer species in primary succession on rocks?

a) Moss
b) Lichen ✅
c) Grass
d) Shrubs

Explanation: Lichens can grow on bare rocks, secreting acids that help in weathering and soil formation.

Q12. In ecological succession, the final stable community is called:

a) Climax community ✅
b) Seral stage
c) Pioneer stage
d) Temporary community

Explanation: A climax community is a stable, self-sustaining community formed after long ecological succession.

Q13. The pyramid of biomass in a sea is generally:

a) Upright
b) Inverted ✅
c) Cylindrical
d) None

Explanation: In aquatic ecosystems, phytoplankton (producers) have less biomass than zooplankton (consumers), so the pyramid is inverted.

Q14. The biotic component of an ecosystem includes:

a) Water
b) Temperature
c) Plants ✅
d) Minerals

Explanation: Biotic components are living organisms like plants, animals, and microbes.

Q15. In a food chain, 10% law was given by:

a) Charles Darwin
b) Lindeman ✅
c) Odum
d) Wallace

Explanation: Lindeman proposed the 10% law, which states that only 10% of energy is transferred from one trophic level to the next.

Q16. Which of the following is an example of ecological pyramid of number inverted?

a) Grassland ecosystem
b) Pond ecosystem
c) Tree ecosystem ✅
d) Desert ecosystem

Explanation: In a tree ecosystem, one tree supports many herbivores and even more parasites, so the pyramid of numbers is inverted.

Q17. The rate at which organic matter is stored by producers is called:

a) Gross primary productivity ✅
b) Net primary productivity
c) Secondary productivity
d) Tertiary productivity

Explanation: Gross primary productivity (GPP) is the total rate of photosynthesis, including energy used in respiration.

Q18. The net primary productivity is equal to:

a) GPP – Plant respiration ✅
b) GPP + Plant respiration
c) GPP × Plant respiration
d) None

Explanation: Net primary productivity (NPP) is the energy available to consumers after subtracting respiration losses from GPP.

Q19. Which of the following pairs are mismatched?

a) Herbivore – Cow
b) Carnivore – Lion
c) Decomposer – Fungi
d) Producer – Mushroom ✅

Explanation: Mushrooms are fungi, decomposers, not producers.

Q20. Which one is an artificial ecosystem?

a) Pond
b) Aquarium ✅
c) Forest
d) Lake

Explanation: Aquarium is human-made, while others are natural ecosystems.

Q21. Biogeochemical cycles ensure that:

a) Energy flows continuously
b) Nutrients are recycled ✅
c) Ecosystems collapse
d) Sunlight is absorbed

Explanation: Biogeochemical cycles recycle essential elements like carbon, nitrogen, and phosphorus in nature.

Q22. A community with several alternative pathways of energy flow is called:

a) Food chain
b) Food web ✅
c) Energy pyramid
d) Trophic cascade

Explanation: Food webs are complex networks of interconnected food chains, ensuring ecosystem stability.

Q23. Which among the following is a primary consumer?

a) Tiger
b) Rabbit ✅
c) Hawk
d) Snake

Explanation: Rabbits feed on grass, making them herbivores and primary consumers.

Q24. Secondary succession occurs on:

a) Bare rock
b) Newly formed sand
c) Abandoned farmland ✅
d) Newly formed volcanic island

Explanation: Secondary succession occurs in areas where life previously existed but was destroyed, like abandoned farmland.

Q25. The organisms which can fix atmospheric nitrogen are:

a) Rhizobium ✅
b) Penicillium
c) Plasmodium
d) E. coli

Explanation: Rhizobium, in root nodules of legumes, converts atmospheric nitrogen into usable nitrogen compounds.

🌱 Ecology and Environment – Ecosystem MCQs

Part 2: Q26–Q50

Q26. Which of the following is a renewable resource?

a) Coal
b) Petroleum
c) Forest ✅
d) Natural gas

Explanation: Forests regenerate naturally if conserved properly, making them a renewable resource, unlike fossil fuels.

Q27. Which zone of a lake has the maximum photosynthetic activity?

a) Profundal zone
b) Benthic zone
c) Littoral zone ✅
d) Abyssal zone

Explanation: The littoral zone receives maximum sunlight and supports the highest photosynthetic activity.

Q28. Which of the following is not a greenhouse gas?

a) Carbon dioxide
b) Methane
c) Nitrous oxide
d) Oxygen ✅

Explanation: Oxygen is not a greenhouse gas; CO₂, CH₄, and N₂O trap heat and contribute to global warming.

Q29. The term “ecology” was coined by:

a) Haeckel ✅
b) Odum
c) Lindeman
d) Darwin

Explanation: Ernst Haeckel coined the term “ecology” in 1866 to describe the study of organisms in relation to their environment.

Q30. The study of inter-relationships between living organisms and their environment is called:

a) Anatomy
b) Ecology ✅
c) Taxonomy
d) Cytology

Explanation: Ecology is the branch of biology dealing with the interactions of organisms with each other and their environment.

Q31. The pyramid of number in a grassland ecosystem is:

a) Upright ✅
b) Inverted
c) Cylindrical
d) None

Explanation: In grasslands, producers (grasses) are abundant, herbivores fewer, and carnivores even fewer, forming an upright pyramid.

Q32. Which is an example of ex-situ conservation?

a) Sacred groves
b) National parks
c) Gene bank ✅
d) Biosphere reserves

Explanation: Ex-situ conservation means protecting species outside their natural habitat, e.g., seed banks, gene banks, zoos.

Q33. Which one is the largest reservoir of carbon on Earth?

a) Atmosphere
b) Ocean ✅
c) Plants
d) Fossil fuels

Explanation: Oceans store the largest amount of carbon in the form of dissolved carbon dioxide and carbonates.

Q34. Which of the following is a xerophyte?

a) Mango
b) Cactus ✅
c) Lotus
d) Rice

Explanation: Xerophytes (e.g., cactus) are adapted to dry conditions with features like thick cuticle and spines.

Q35. An ecosystem without producers cannot exist because:

a) Consumers will not survive ✅
b) Decomposers will multiply
c) Energy will not flow
d) Both a and c

Explanation: Producers are the base of food chains; without them, energy cannot enter or flow through the ecosystem.

Q36. The ecological niche of an organism refers to:

a) Its habitat only
b) Its trophic level only
c) Role played by it in ecosystem ✅
d) Place of living and nothing else

Explanation: An ecological niche includes habitat, trophic role, and interactions of a species with biotic and abiotic factors.

Q37. The term “ecosystem” was first coined by:

a) A.G. Tansley ✅
b) Odum
c) Linnaeus
d) Haeckel

Explanation: A.G. Tansley introduced the concept of ecosystem in 1935.

Q38. In an ecosystem, the 10% energy transfer law is related to:

a) Lindeman ✅
b) Darwin
c) Wallace
d) Haeckel

Explanation: Lindeman proposed the 10% law, stating only about 10% of energy is passed to the next trophic level.

Q39. Biotic potential refers to:

a) Ability of environment to support life
b) Rate of increase of population under ideal conditions ✅
c) Number of organisms a habitat can support
d) Limiting factor of population

Explanation: Biotic potential is the maximum reproductive capacity of a population under ideal conditions.

Q40. Carrying capacity of an environment is determined by:

a) Reproductive capacity of species
b) Limiting resources ✅
c) Biotic potential
d) Environmental resistance alone

Explanation: Carrying capacity is the maximum population size an environment can sustain due to limited resources.

Q41. Which one of the following is not an ecosystem service?

a) Purification of air
b) Cycling of nutrients
c) Soil formation
d) Mining of coal ✅

Explanation: Mining of coal is a human activity, not a natural ecosystem service.

Q42. The hydrological cycle refers to:

a) Recycling of oxygen
b) Circulation of water ✅
c) Cycling of nitrogen
d) Cycling of carbon

Explanation: The hydrological cycle involves continuous circulation of water through evaporation, condensation, and precipitation.

Q43. Which ecosystem shows the maximum biomass of producers?

a) Desert
b) Grassland
c) Forest ✅
d) Ocean

Explanation: Forest ecosystems have large trees and dense vegetation, contributing to maximum producer biomass.

Q44. The pyramid of biomass in a forest ecosystem is:

a) Upright ✅
b) Inverted
c) Cylindrical
d) Irregular

Explanation: In forests, producer biomass (trees) is higher than consumers, so the pyramid is upright.

Q45. Which of the following cycles does not have an atmospheric phase?

a) Nitrogen cycle
b) Carbon cycle
c) Phosphorus cycle ✅
d) Oxygen cycle

Explanation: Phosphorus cycle occurs mainly through rocks and soil, with no major atmospheric phase.

Q46. Which one is an abiotic component of an ecosystem?

a) Fungi
b) Plants
c) Bacteria
d) Temperature ✅

Explanation: Abiotic components are non-living factors like temperature, light, water, and soil.

Q47. Which ecological pyramid can be inverted in both terrestrial and aquatic ecosystems?

a) Pyramid of number
b) Pyramid of biomass ✅
c) Pyramid of energy
d) All of these

Explanation: Pyramid of biomass can be inverted in aquatic ecosystems (phytoplankton vs. zooplankton) and sometimes terrestrial ecosystems.

Q48. Decomposers obtain their nutrition from:

a) Living hosts
b) Dead organic matter ✅
c) Photosynthesis
d) Inorganic materials

Explanation: Decomposers like fungi and bacteria feed on dead organic matter, recycling nutrients.

Q49. The interaction between cattle and grass is:

a) Parasitism
b) Predation ✅
c) Commensalism
d) Amensalism

Explanation: Grazing cattle feed on grass, which is a form of predation (herbivory is a type of predation).

Q50. Which of the following represents secondary succession?

a) Growth of vegetation on bare rock
b) Reappearance of forest after forest fire ✅
c) Colonization of new volcanic island
d) Formation of soil from lava

Explanation: Secondary succession occurs where life existed earlier but was destroyed, e.g., after forest fire or flood.

🌱 Ecology and Environment – Ecosystem MCQs

Part 3: Q51–Q75

Q51. Which is the largest man-made aquatic ecosystem?

a) Pond
b) Lake
c) Reservoir ✅
d) Aquarium

Explanation: Reservoirs created by dams for irrigation, drinking water, and electricity are the largest man-made aquatic ecosystems.

Q52. Which of the following is a primary succession?

a) Colonization of lichens on bare rock ✅
b) Reappearance of weeds on abandoned farmland
c) Regeneration of forest after fire
d) Growth of algae in pond water

Explanation: Primary succession begins in lifeless areas (bare rock, lava) where soil is initially absent. Lichens are pioneers.

Q53. Which is an example of commensalism?

a) Cattle egret and cattle ✅
b) Lichen
c) Tick and dog
d) Lion and deer

Explanation: In commensalism, one benefits while the other is unaffected. Egrets benefit by feeding on insects stirred by cattle.

Q54. In an ecosystem, energy loss occurs mainly through:

a) Decomposition
b) Respiration ✅
c) Photosynthesis
d) Predation

Explanation: A large portion of energy is lost as heat during respiration, limiting energy transfer to the next trophic level.

Q55. Which one is an autotroph in an aquatic ecosystem?

a) Zooplankton
b) Phytoplankton ✅
c) Fish
d) Frog

Explanation: Phytoplankton are microscopic algae that perform photosynthesis and act as producers.

Q56. An example of a parasitic relationship is:

a) Algae and fungi in lichen
b) Mosquito and human ✅
c) Cow and grass
d) Cattle egret and buffalo

Explanation: Mosquito feeds on human blood, harming the host while benefiting itself → parasitism.

Q57. An ecological pyramid that can never be inverted is:

a) Pyramid of biomass
b) Pyramid of number
c) Pyramid of energy ✅
d) All of these

Explanation: Pyramid of energy is always upright, as energy decreases progressively at higher trophic levels.

Q58. Which is an example of mutualism?

a) Orchid growing on a tree
b) Rhizobium in root nodules ✅
c) Tapeworm in intestine
d) Tiger and deer

Explanation: Rhizobium provides nitrogen to the plant, while the plant supplies food → both benefit (mutualism).

Q59. The amount of energy fixed by producers in an ecosystem is called:

a) Net primary productivity
b) Gross primary productivity ✅
c) Secondary productivity
d) Trophic energy

Explanation: GPP is the total rate at which producers capture and store energy as biomass.

Q60. The net primary productivity is maximum in:

a) Tundra
b) Grassland
c) Tropical rainforest ✅
d) Desert

Explanation: High rainfall, temperature, and biodiversity make tropical rainforests most productive.

Q61. Which of the following is an r-strategist species?

a) Elephant
b) Human
c) Cockroach ✅
d) Whale

Explanation: r-strategists (e.g., cockroaches) reproduce quickly, produce many offspring, and have short life spans.

Q62. The interaction where both species are harmed is called:

a) Mutualism
b) Competition ✅
c) Amensalism
d) Predation

Explanation: In competition, both species lose because they compete for the same limited resource.

Q63. The vertical distribution of different species in a community is called:

a) Stratification ✅
b) Succession
c) Climax
d) Niche

Explanation: Stratification refers to layers (e.g., trees, shrubs, herbs) in forests due to different light and space requirements.

Q64. The 10% energy transfer law explains:

a) Energy recycling
b) Decrease of energy at higher trophic levels ✅
c) Increase in biomass
d) Nutrient recycling

Explanation: Only about 10% of energy is passed on to the next trophic level; the rest is lost as heat.

Q65. Which is the most stable ecosystem?

a) Desert
b) Ocean ✅
c) Grassland
d) Forest

Explanation: Oceans are vast, with huge buffering capacity, making them the most stable ecosystem.

Q66. Secondary productivity refers to:

a) Rate of energy storage by producers
b) Rate of energy storage by consumers ✅
c) Rate of decomposition by bacteria
d) Rate of energy loss

Explanation: Secondary productivity is the rate at which consumers (animals) convert food into biomass.

Q67. Which type of succession takes place in a pond?

a) Primary succession ✅
b) Secondary succession
c) Tertiary succession
d) Retrogressive succession

Explanation: Succession in a pond starts from open water (phytoplankton → aquatic plants → grasses → forest), hence primary succession.

Q68. The ozone layer is present in:

a) Troposphere
b) Stratosphere ✅
c) Mesosphere
d) Thermosphere

Explanation: The ozone layer, located in the stratosphere, protects life by absorbing harmful UV radiation.

Q69. Which of the following is a density-independent factor?

a) Competition
b) Predation
c) Flood ✅
d) Parasitism

Explanation: Floods affect populations regardless of their size, hence density-independent.

Q70. A group of individuals of the same species in an area is called:

a) Community
b) Population ✅
c) Ecosystem
d) Biome

Explanation: A population consists of all individuals of the same species in a given area at a given time.

Q71. Which ecosystem shows the inverted pyramid of number?

a) Forest ✅
b) Grassland
c) Pond
d) Desert

Explanation: In forests, one tree (producer) supports many herbivores and parasites, leading to an inverted pyramid of numbers.

Q72. Which ecosystem is least productive?

a) Ocean
b) Desert ✅
c) Grassland
d) Rainforest

Explanation: Deserts have extreme climates and scarce vegetation, leading to the lowest productivity.

Q73. Which of the following is an example of amensalism?

a) Algae and fungi in lichen
b) Penicillium and bacteria ✅
c) Cow and grass
d) Lion and deer

Explanation: Penicillium secretes penicillin that kills bacteria; Penicillium is unaffected while bacteria are harmed → amensalism.

Q74. In a food chain, if the number of producers is 5000, herbivores 500, then carnivores will be approximately:

a) 5 ✅
b) 50
c) 500
d) 5000

Explanation: Energy reduces 10-fold at each trophic level (10% law), so carnivores would be much fewer, around 5.

Q75. The rate at which food energy is assimilated at each trophic level is called:

a) Productivity ✅
b) Stability
c) Carrying capacity
d) Potential

Explanation: Productivity is the rate of biomass/energy accumulation in an ecosystem at different trophic levels.

🌱 Ecology and Environment – Ecosystem MCQs

Part 4: Q76–Q100

Q76. Which of the following is a secondary consumer in a pond ecosystem?

a) Phytoplankton
b) Zooplankton
c) Small fish ✅
d) Bacteria

Explanation: Small fish feed on zooplankton (primary consumers), making them secondary consumers.

Q77. The primary source of nitrogen for plants is:

a) Atmospheric N₂
b) Nitrate and ammonium ions ✅
c) Proteins in soil
d) Nitrous oxide

Explanation: Plants absorb nitrogen mainly in the form of nitrates (NO₃⁻) and ammonium (NH₄⁺).

Q78. The producers in a mangrove ecosystem are mainly:

a) Algae ✅
b) Crabs
c) Fishes
d) Birds

Explanation: Algae and mangrove trees are primary producers that support the mangrove food web.

Q79. Which of the following represents a detritus food chain?

a) Grass → Rabbit → Fox
b) Phytoplankton → Fish → Man
c) Dead leaves → Earthworm → Crow ✅
d) Grass → Cow → Human

Explanation: Detritus food chain starts with dead organic matter consumed by decomposers or detritivores.

Q80. Which type of biome is dominated by coniferous forests?

a) Tundra
b) Taiga ✅
c) Desert
d) Grassland

Explanation: Taiga (boreal forest) is dominated by coniferous trees such as pine, spruce, and fir.

Q81. Which cycle involves both sedimentary and gaseous phases?

a) Phosphorus cycle
b) Sulphur cycle ✅
c) Nitrogen cycle
d) Carbon cycle

Explanation: Sulphur cycle has a gaseous phase (SO₂, H₂S) and a sedimentary phase (sulphates in rocks).

Q82. The self-regulating capacity of an ecosystem is called:

a) Homeostasis ✅
b) Ecotone
c) Productivity
d) Stability

Explanation: Homeostasis is the ability of an ecosystem to maintain stability and balance through self-regulation.

Q83. Which is the largest terrestrial biome?

a) Tropical rainforest
b) Desert
c) Taiga ✅
d) Grassland

Explanation: Taiga (boreal forest) is the largest terrestrial biome, covering vast areas of North America, Europe, and Asia.

Q84. The ecological pyramid of energy in the sea is:

a) Upright ✅
b) Inverted
c) Irregular
d) None

Explanation: The energy pyramid is always upright in all ecosystems, including the sea.

Q85. Which one is the most productive aquatic ecosystem?

a) Pond
b) Ocean
c) Estuary ✅
d) Lake

Explanation: Estuaries are highly productive due to nutrient availability and mixing of fresh and salt water.

Q86. The transfer of energy from one trophic level to another is called:

a) Energy fixation
b) Energy flow ✅
c) Energy recycling
d) Productivity

Explanation: Energy flow refers to the movement of energy through the food chain from producers to consumers.

Q87. Which organisms are responsible for returning nutrients to the soil?

a) Herbivores
b) Decomposers ✅
c) Carnivores
d) Omnivores

Explanation: Decomposers (fungi, bacteria) break down organic matter and recycle nutrients into the soil.

Q88. Which is a keystone species in many ecosystems?

a) Tiger ✅
b) Rabbit
c) Grass
d) Ant

Explanation: Tigers regulate herbivore populations, maintaining ecosystem balance → keystone species.

Q89. Which of the following is an example of in-situ conservation?

a) Botanical garden
b) National park ✅
c) Zoo
d) Gene bank

Explanation: In-situ conservation protects species in their natural habitat, such as national parks and sanctuaries.

Q90. Which of the following best describes ecological succession?

a) Seasonal changes in a habitat
b) Natural replacement of species over time ✅
c) Sudden destruction of habitat
d) Animal migration

Explanation: Ecological succession is the gradual replacement of one community by another until a climax community forms.

Q91. The grazing food chain always starts with:

a) Decomposers
b) Green plants ✅
c) Herbivores
d) Omnivores

Explanation: The grazing food chain begins with autotrophs (green plants) consumed by herbivores.

Q92. Ecotone is a:

a) Zone of transition between two ecosystems ✅
b) Stable climax community
c) Decomposer habitat
d) Primary succession stage

Explanation: An ecotone is the transitional zone between two ecosystems, rich in biodiversity.

Q93. Which one is an example of a pioneer species in primary succession in water?

a) Fish
b) Phytoplankton ✅
c) Zooplankton
d) Shrubs

Explanation: In aquatic succession, phytoplankton are the pioneer species that initiate the process.

Q94. The community that remains stable and in equilibrium with the environment is called:

a) Seral stage
b) Climax community ✅
c) Transitional community
d) Pioneer community

Explanation: The climax community is stable, self-sustaining, and in equilibrium with the environment.

Q95. Which of the following is an example of retrogressive succession?

a) Grass growing on bare rock
b) Forest destroyed by overgrazing ✅
c) Colonization of lichens on lava
d) Growth of algae in a pond

Explanation: Retrogressive succession occurs when a stable community is degraded into a simpler one due to disturbances (e.g., overgrazing).

Q96. The grazing food chain derives its energy from:

a) Detritus
b) Living green plants ✅
c) Dead organic matter
d) Fungi

Explanation: Grazing food chain starts with producers (green plants) which are grazed by herbivores.

Q97. In a stable ecosystem, the number of trophic levels is usually limited to:

a) 2–3
b) 3–4 ✅
c) 5–6
d) 7–8

Explanation: Energy loss at each level restricts the number of trophic levels to about 3–4 in most ecosystems.

Q98. The organisms that feed at all trophic levels are:

a) Producers
b) Herbivores
c) Omnivores ✅
d) Primary consumers

Explanation: Omnivores feed on both plants and animals, sometimes at multiple trophic levels.

Q99. Which one is the most stable aquatic ecosystem?

a) River
b) Pond
c) Ocean ✅
d) Lake

Explanation: Oceans, being vast and deep, show the highest stability among aquatic ecosystems.

Q100. The ecological principle of energy flow is governed by:

a) First law of thermodynamics
b) Second law of thermodynamics ✅
c) Law of segregation
d) Hardy-Weinberg principle

Explanation: Energy flow follows the second law of thermodynamics, as energy transfer is inefficient and lost as heat.

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