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Ecosystem — NEET MCQs with answers
Chapter 12 examines the ecosystem as a functional unit in which biotic and abiotic components interact, with productivity, decomposition, energy flow and nutrient cycling as its functions. Using a pond as an example, it traces energy from the sun through producers and consumers to decomposers, and explains the ecological pyramids of number, biomass and energy.
Topics in this chapter
- 12.1 Ecosystem Structure and Function
- 12.2 Productivity
- 12.3 Decomposition
- 12.4 Energy Flow
- 12.5 Ecological Pyramids
Free practice questions
During decomposition, the gas released among the inorganic substances is:
- A. Carbon dioxide
- B. Hydrogen
- C. Methane
- D. Nitrogen gas
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Answer: A — Decomposers break complex organic matter into inorganic substances like carbon dioxide, water and nutrients — carbon dioxide is the gas released.
NCERT Class 12 Biology · Ch 12 · 12.3 Decomposition
In a grassland ecosystem, which trophic level has the greatest number of organisms?
- A. The secondary consumers
- B. The tertiary consumers
- C. The top carnivores
- D. The producers
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Answer: D — In a grassland pyramid of numbers (Figure 12.4a), producers (grasses) are most numerous — nearly 6 million plants form the broad base, while only three top-carnivores are supported at the apex.
NCERT Class 12 Biology · Ch 12 · 12.5 Ecological Pyramids
For convenience, ecosystems are divided into two basic categories, namely:
- A. Abiotic and biotic
- B. Terrestrial and aquatic
- C. Producer and consumer
- D. Natural and artificial
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Answer: B — Since the biosphere is too big and complex, it is convenient to divide it into two basic categories: terrestrial and aquatic.
NCERT Class 12 Biology · Ch 12 · 12.1 Ecosystem — Structure and Function
For a phytoplankton community GPP = 12 g C m^-2 day^-1 and R = 9 g C m^-2 day^-1. Its NPP as a percentage of GPP is:
- A. 50%
- B. 25%
- C. 75%
- D. 33%
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Answer: B — NPP = 12 - 9 = 3; NPP/GPP = 3/12 = 25%.
NCERT Class 12 Biology · Ch 12 · 12.2 Productivity
Herbivores (primary consumers) belong to which trophic level?
- A. Second trophic level
- B. Fourth trophic level
- C. First trophic level
- D. Third trophic level
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Answer: A — NCERT: 'Producers belong to the first trophic level, herbivores (primary consumer) to the second.'
NCERT Class 12 Biology · Ch 12 · 12.4 Energy Flow
Which of the following constitutes detritus?
- A. Living plant roots and shoots
- B. Only water-soluble mineral salts
- C. Dead plant remains and dead animal remains including faecal matter
- D. Green photosynthetic tissue only
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Answer: C — Dead plant remains such as leaves, bark, flowers and dead remains of animals, including faecal matter, constitute detritus.
NCERT Class 12 Biology · Ch 12 · 12.3 Decomposition
The vertical distribution of different species occupying different levels in an ecosystem is called:
- A. Species composition
- B. Zonation
- C. Stratification
- D. Succession
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Answer: C — Vertical distribution of different species occupying different levels is called stratification.
NCERT Class 12 Biology · Ch 12 · 12.1 Ecosystem — Structure and Function
Which of the following is true regarding the direction of energy through trophic levels, reflected in the energy pyramid?
- A. Energy flows in a cycle among trophic levels
- B. Energy decreases at successive higher trophic levels
- C. Energy remains identical at every level
- D. Energy increases at successive higher trophic levels
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Answer: B — NCERT states there is a unidirectional movement of energy towards higher trophic levels with dissipation and loss as heat, and that the amount of energy decreases at successive trophic levels, keeping the energy pyramid upright.
NCERT Class 12 Biology · Ch 12 · 12.4-12.5
Ecosystem P: GPP 2000, R 500. Ecosystem Q: GPP 1800, R 200. Which has the higher NPP and higher respiration percentage respectively?
- A. Both same NPP
- B. Higher NPP: P; higher respiration %: Q
- C. Higher NPP: P; higher respiration %: P
- D. Higher NPP: Q; higher respiration %: P
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Answer: D — NPP_P = 1500, NPP_Q = 1600 (Q higher NPP). Respiration %: P = 25%, Q ≈ 11% (P higher %). So higher NPP = Q, higher respiration % = P.
NCERT Class 12 Biology · Ch 12 · 12.2 Productivity
Plants capture only 2-10 per cent of the:
- A. Total incident solar radiation
- B. Infrared radiation reaching Earth
- C. Energy stored in detritus
- D. Photosynthetically active radiation (PAR)
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Answer: D — NCERT: 'Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world.' The 2-10% is captured out of the PAR, not out of total solar radiation.
NCERT Class 12 Biology · Ch 12 · 12.4 Energy Flow
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