Environment, Ecology & Climate Change – Ecology and Ecosystems
Assam Public Service Commission (APSC)
Combined Competitive Examination (CCE) – Preliminary Examination
General Studies Paper I (Objective, 200 Marks)
Topic: Environment, Ecology & Climate Change
Sub-Topic: Ecology and Ecosystems
Ecology and Ecosystems – Multiple Choice Questions (MCQs) with Answers & Explanations
Q1. Ecology is the study of:
A. Plants only
B. Animals only
C. Interaction between organisms and their environment
D. Atmospheric processes
Correct Answer: C
Explanation:
Ecology examines relationships between living organisms and their physical environment, including energy flow and nutrient cycles.
Q2. An ecosystem consists of:
A. Only plants
B. Only animals
C. Living and non-living components
D. Soil and water only
Correct Answer: C
Explanation:
An ecosystem includes biotic (plants, animals, microbes) and abiotic (air, water, soil, light) components.
Q3. Which of the following is a biotic component?
A. Temperature
B. Sunlight
C. Bacteria
D. Water
Correct Answer: C
Explanation:
Biotic components are living organisms; bacteria are living microorganisms.
Q4. Producers in an ecosystem are:
A. Carnivores
B. Herbivores
C. Green plants
D. Decomposers
Correct Answer: C
Explanation:
Green plants are producers because they manufacture food through photosynthesis.
Q5. Consumers that feed directly on producers are called:
A. Secondary consumers
B. Tertiary consumers
C. Primary consumers
D. Decomposers
Correct Answer: C
Explanation:
Primary consumers are herbivores that feed on plants.
Q6. Which organisms break down dead organic matter?
A. Producers
B. Herbivores
C. Carnivores
D. Decomposers
Correct Answer: D
Explanation:
Decomposers like bacteria and fungi recycle nutrients back into the ecosystem.
Q7. The flow of energy in an ecosystem is:
A. Cyclic
B. Bidirectional
C. Unidirectional
D. Random
Correct Answer: C
Explanation:
Energy flows one-way from the sun → producers → consumers → decomposers.
Q8. A food chain represents:
A. Cycling of nutrients
B. Flow of energy
C. Population growth
D. Habitat diversity
Correct Answer: B
Explanation:
A food chain shows energy transfer from one trophic level to another.
Q9. Which trophic level has maximum energy?
A. Tertiary consumers
B. Secondary consumers
C. Primary consumers
D. Producers
Correct Answer: D
Explanation:
Energy is maximum at the producer level and decreases at higher trophic levels.
Q10. The 10% law of energy transfer was proposed by:
A. Darwin
B. Elton
C. Lindeman
D. Odum
Correct Answer: C
Explanation:
Lindeman’s 10% law states that only about 10% of energy is transferred to the next trophic level.
Q11. A food web is:
A. Single food chain
B. Interconnected food chains
C. Energy pyramid
D. Biomass pyramid
Correct Answer: B
Explanation:
A food web shows multiple interconnected food chains, making ecosystems more stable.
Q12. Which pyramid is always upright?
A. Pyramid of numbers
B. Pyramid of biomass
C. Pyramid of energy
D. Pyramid of organisms
Correct Answer: C
Explanation:
The energy pyramid is always upright because energy decreases at each trophic level.
Q13. Which ecosystem has the highest productivity?
A. Desert
B. Grassland
C. Tropical rainforest
D. Tundra
Correct Answer: C
Explanation:
Tropical rainforests have high rainfall, temperature, and biodiversity, leading to maximum productivity.
Q14. Which of the following is a natural ecosystem?
A. Aquarium
B. Crop field
C. Pond
D. Garden
Correct Answer: C
Explanation:
A pond ecosystem develops naturally, unlike artificial ecosystems like aquariums.
Q15. Primary productivity refers to:
A. Energy used by consumers
B. Energy stored by producers
C. Decomposition rate
D. Respiration loss
Correct Answer: B
Explanation:
Primary productivity is the rate of biomass production by producers.
Q16. Which biome is characterized by permafrost?
A. Desert
B. Savanna
C. Tundra
D. Taiga
Correct Answer: C
Explanation:
Tundra has permanently frozen subsoil (permafrost).
Q17. Which nutrient cycle does NOT involve the atmosphere?
A. Nitrogen cycle
B. Carbon cycle
C. Oxygen cycle
D. Phosphorus cycle
Correct Answer: D
Explanation:
The phosphorus cycle lacks a gaseous phase.
Q18. Mutualism is a relationship where:
A. One benefits, other is harmed
B. Both species benefit
C. One benefits, other unaffected
D. Both are harmed
Correct Answer: B
Explanation:
In mutualism, both organisms gain benefits (e.g., lichens).
Q19. Commensalism refers to:
A. Mutual benefit
B. One harmed, one benefited
C. One benefited, other unaffected
D. Both harmed
Correct Answer: C
Explanation:
In commensalism, one species benefits while the other is unaffected.
Q20. Which relationship occurs between a parasite and host?
A. Mutualism
B. Predation
C. Parasitism
D. Commensalism
Correct Answer: C
Explanation:
In parasitism, the parasite benefits at the expense of the host.
Q21. Ecological succession is:
A. Sudden ecosystem destruction
B. Gradual change in species composition
C. Seasonal population change
D. Food chain formation
Correct Answer: B
Explanation:
Ecological succession involves progressive replacement of species over time.
Q22. Primary succession occurs on:
A. Forest land
B. Grassland
C. Bare rock
D. Agricultural land
Correct Answer: C
Explanation:
Primary succession starts on lifeless surfaces like bare rock or lava.
Q23. The first colonizers in primary succession are:
A. Trees
B. Shrubs
C. Lichens
D. Grasses
Correct Answer: C
Explanation:
Lichens are pioneer species that can grow on bare rocks.
Q24. Secondary succession occurs after:
A. Volcanic eruption
B. Glacier retreat
C. Forest fire
D. Lava flow
Correct Answer: C
Explanation:
Secondary succession occurs where soil already exists, such as after forest fires.
Q25. Biodiversity refers to:
A. Number of animals only
B. Variety of plants only
C. Variety of life forms
D. Forest cover
Correct Answer: C
Explanation:
Biodiversity includes genetic, species, and ecosystem diversity.
Q26. Which ecosystem is called the “lungs of the Earth”?
A. Grasslands
B. Deserts
C. Tropical rainforests
D. Tundra
Correct Answer: C
Explanation:
Tropical rainforests absorb large amounts of carbon dioxide and release oxygen.
Q27. Carrying capacity refers to:
A. Maximum population an ecosystem can support
B. Minimum population size
C. Rate of reproduction
D. Migration rate
Correct Answer: A
Explanation:
Carrying capacity is the maximum sustainable population an environment can support.
Q28. Keystone species are those that:
A. Are most abundant
B. Have no ecological role
C. Have a disproportionately large impact
D. Are endangered
Correct Answer: C
Explanation:
Keystone species have critical ecological roles, influencing ecosystem structure.
Q29. Ecological balance is maintained by:
A. Producers only
B. Consumers only
C. Decomposers only
D. Interaction of all components
Correct Answer: D
Explanation:
Balance depends on producers, consumers, decomposers, and abiotic factors.
Q30. The ultimate source of energy for ecosystems is:
A. Wind
B. Water
C. Sun
D. Soil
Correct Answer: C
Explanation:
The Sun is the primary energy source driving all ecosystems.
✅ APSC Prelims Smart Tip
For Ecology & Ecosystems, focus on:
- Definitions and concepts
- Energy flow & trophic levels
- Food chains, food webs, pyramids
- Ecological relationships & succession
- Nutrient cycles and biodiversity
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Ecology MCQs for APSC
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Ecosystem concepts MCQs prelims
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Food chain food web MCQs
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Energy pyramid ecology questions
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Ecological succession MCQs APSC
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Biodiversity and ecosystems MCQs
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Environment GS Paper I ecology