Unit 3 — MCQ Practice Bank: 27 questions based on the official MGSU syllabus and PYQ analysis. Tap Show Answer to check yourself. 🔥 = high priority, ⭐ = important.
Q1. Who coined the term 'ecosystem'? PYQ 2023 🔥
- Eugene Odum
- Arthur Tansley
- Raymond Lindeman
- Charles Darwin
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Answer: B — Arthur Tansley coined the term 'ecosystem' in 1935.
Q2. The prefix 'eco' in 'ecosystem' comes from the Greek word 'oikos', which means: Expected
- Life
- Study
- House
- Balance
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Answer: C — 'Oikos' means 'house' — the ecosystem is the house where living and non-living things interact.
Q3. Which of the following is called the functional unit of nature? Expected
- Ecosystem
- Community
- Population
- Biome
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Answer: A — The ecosystem is the functional unit of nature, where biotic and abiotic parts work together as one unit.
Q4. Which of the following is a biotic component of an ecosystem? Expected
- Sunlight
- Temperature
- Soil minerals
- Decomposers
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Answer: D — Decomposers (bacteria, fungi) are living; sunlight, temperature and minerals are non-living abiotic factors.
Q5. Which of the following is NOT an abiotic factor? Expected
- Rainfall
- Bacteria
- Wind
- Minerals
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Answer: B — Bacteria are living organisms (biotic); rainfall, wind and minerals are non-living abiotic factors.
Q6. The three functional processes of an ecosystem are: Expected
- Photosynthesis, respiration and decomposition
- Production, consumption and excretion
- Energy flow, nutrient cycling and ecological succession
- Birth, growth and death
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Answer: C — An ecosystem works through energy flow, nutrient cycling and ecological succession.
Q7. Which statement correctly contrasts energy and nutrients in an ecosystem? Expected ⭐
- Energy flows one way and is lost as heat; nutrients cycle round and round
- Both energy and nutrients cycle continuously
- Both energy and nutrients flow in one direction only
- Nutrients flow one way while energy cycles back
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Answer: A — Energy moves one-way (sun to producers to consumers, lost as heat); nutrients like carbon and nitrogen are reused in cycles.
Q8. Producers are also known as: Expected
- Heterotrophs
- Autotrophs
- Decomposers
- Detritivores
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Answer: B — Producers make their own food, so they are autotrophs (photoautotrophs like green plants, or chemoautotrophs like some bacteria).
Q9. Primary consumers are: Expected 🔥
- Carnivores
- Omnivores
- Herbivores
- Decomposers
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Answer: C — Primary consumers eat producers directly, so they are herbivores (rabbit, deer, grasshopper, cow).
Q10. Decomposers mainly include: Expected ⭐
- Bacteria and fungi
- Earthworms and millipedes
- Algae and protozoa
- Insects and spiders
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Answer: A — Bacteria and fungi break down dead organisms and recycle nutrients back to the soil.
Q11. An earthworm feeding on dead leaves is an example of a: Expected
- Producer
- Primary consumer
- Decomposer
- Detritivore
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Answer: D — Detritivores eat detritus (dead organic matter); decomposers like bacteria chemically break it down further.
Q12. In the food chain Grass → Rabbit → Fox → Lion, the fox is a: Expected
- Primary consumer
- Secondary consumer
- Tertiary consumer
- Producer
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Answer: B — The fox eats the herbivore (rabbit), making it a secondary consumer; the lion is the tertiary (top) consumer.
Q13. A grazing food chain always begins with: Expected ⭐
- Dead organic matter
- Decomposers
- Living green producers
- Detritivores
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Answer: C — Grazing chains start from living producers; detritus chains start from dead organic matter.
Q14. Dead leaves → Earthworm → Bird is an example of a: Expected
- Detritus food chain
- Grazing food chain
- Parasitic food chain
- Aquatic food chain
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Answer: A — It begins with dead organic matter, the hallmark of a detritus food chain.
Q15. A food web is more stable than a single food chain because: Expected ⭐
- It has fewer trophic levels
- It involves only producers
- Energy flows faster through it
- Each animal has alternate food sources
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Answer: D — In a web, food chains interconnect, so if one food source disappears the animal can eat something else.
Q16. Ecological pyramids are also known as: Expected
- Darwinian pyramids
- Eltonian pyramids
- Odum pyramids
- Lindeman pyramids
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Answer: B — Named after Charles Elton (1927), who first described ecological pyramids.
Q17. The pyramid of ___ is always upright and can never be inverted. PYQ Dec 2024 🔥
- Numbers
- Biomass
- Energy
- Population
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Answer: C — Energy is lost as heat at every transfer, so the energy pyramid is always upright; numbers and biomass can sometimes be inverted.
Q18. The pyramid of numbers can be inverted in the case of: Expected ⭐
- One large tree supporting many insects
- A grassland with many herbivores
- A pond ecosystem
- A desert food chain
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Answer: A — A single producer (tree) can support numerous primary consumers (insects), inverting the numbers pyramid.
Q19. In aquatic ecosystems, the pyramid of biomass is sometimes inverted because: Expected
- Fish eat phytoplankton too fast
- The standing biomass of phytoplankton can be less than that of zooplankton
- Water absorbs all the energy
- Decomposers are absent in water
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Answer: B — Phytoplankton reproduce rapidly, but their standing biomass at any given moment can be smaller than the zooplankton feeding on them.
Q20. Lindeman's 10% law (1942) states that: Expected 🔥
- Only 10% of sunlight is used by producers
- Only about 10% of the energy at one trophic level passes to the next
- Only 10% of species in an ecosystem are producers
- Biomass decreases by exactly 10% every year
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Answer: B — Only about 10% of energy transfers to the next trophic level; roughly 90% is lost as heat through respiration, movement and waste.
Q21. If grass (producers) holds 10,000 kcal of energy, about how much energy reaches the hawk (tertiary consumer)? Expected ⭐
- 1,000 kcal
- 100 kcal
- 10 kcal
- 1 kcal
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Answer: C — 10,000 → 1,000 (rabbit) → 100 (fox) → 10 (hawk): roughly 10% of energy passes at each trophic level.
Q22. Food chains rarely have more than 4–5 trophic levels because: Expected
- Too little energy remains after repeated 90% losses at each transfer
- Top carnivores refuse to eat further
- Decomposers stop working beyond that point
- Producers cannot grow beyond a fixed limit
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Answer: A — With about 90% of energy lost as heat at every step, higher trophic levels simply do not receive enough energy to sustain more levels.
Q23. The pioneer species in primary succession on bare rock are usually: Expected
- Grasses and shrubs
- Lichens and mosses
- Large trees
- Aquatic plants
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Answer: B — Lichens and mosses are the first organisms to colonise lifeless surfaces, beginning the process of soil formation.
Q24. The climax community represents which stage of ecological succession? PYQ Dec 2024 🔥
- The first stage
- The fastest stage
- An unstable middle stage
- The final, stable stage
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Answer: D — The climax community is the final, stable stage (usually a forest) toward which succession develops.
Q25. Primary succession is slower than secondary succession because it: Expected
- Receives more rainfall
- Involves a greater number of species
- Starts on a bare, lifeless surface with no soil
- Occurs only in aquatic environments
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Answer: C — Primary succession begins where no soil exists (bare rock, lava flow), so soil must form first; secondary succession starts where soil already exists.
Q26. The series of developmental stages in ecological succession is called a: Expected
- Sere
- Biome
- Niche
- Ecotone
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Answer: A — A sere is the sequence of stages from pioneer species to the climax community.
Q27. The water of an estuary is best described as: Expected ⭐
- Completely fresh
- Completely saline
- Heavily polluted
- Brackish
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Answer: D — Estuaries mix river and sea water, making it brackish — neither fully fresh nor fully saline — and highly productive.
