Chapter Exam

Chapter 12: Ecosystem — Online MCQ Test

Q: Which of the following is an abiotic component of an ecosystem?

Answer: C. Temperature — Abiotic components are non-living factors such as temperature, light, water and soil. Producers, consumers and decomposers are biotic components.

Q: The vertical distribution of different species occupying different levels in an ecosystem is called:

Answer: A. Stratification — Stratification refers to the vertical layering of organisms, such as trees, shrubs and herbs in a forest ecosystem.

Q: Gross primary productivity is the rate of production of organic matter by producers during:

Answer: B. Photosynthesis — Gross primary productivity is the total organic matter produced by plants during photosynthesis per unit area per unit time.

Q: Fill in the blank: Net primary productivity is equal to gross primary productivity minus ________.

Answer: A. Respiration loss — Net primary productivity is calculated as NPP = GPP - R, where R is respiration loss.

Q: If the gross primary productivity of an ecosystem is 1200 kcal m−2 yr−1 and respiration loss is 500 kcal m−2 yr−1, what is its net primary productivity?

Answer: B. 700 kcal m−2 yr−1 — NPP = GPP - R. Therefore, NPP = 1200 - 500 = 700 kcal m−2 yr−1.

Q: Which of the following best describes a food web?

Answer: B. A network of interconnected food chains — A food web is formed by interconnection of several food chains, providing alternate pathways of energy flow.

Q: A forest has many plant layers such as tall trees, smaller trees, shrubs and herbs. This is an example of:

Answer: B. Stratification — Vertical layering of vegetation in a forest is called stratification, a structural feature of ecosystems.

Q: If an ecosystem receives 1,000,000 J of solar energy and producers fix 1 percent of it, how much energy will be available to secondary consumers according to the 10 percent law?

Answer: B. 100 J — Producers fix 1 percent of 1,000,000 J = 10,000 J. Herbivores get 1,000 J and secondary consumers get 100 J.

Q: Consider the sequence: detritus → humus → inorganic nutrients. Which option correctly represents the processes mainly responsible for these changes?

Answer: B. Humification followed by mineralisation — Humification leads to the formation of humus from detritus, and mineralisation releases inorganic nutrients from humus.

BIOLOGY · Grade 12 · CBSE(NCERT)

Practice Chapter 12: Ecosystem with a free chapter-wise online MCQ test for CBSE(NCERT) Grade 12 BIOLOGY. This chapter covers: Ecosystem Biotic Components Abiotic Components Food Chain Food Web Energy Flow Ecological Pyramid Primary Productivity Decomposition Nutrient Cycling Biomass. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter 12: Ecosystem — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 12 BIOLOGY — Chapter 12: Ecosystem, with answers and explanations. These are sample questions; the exam has its own separate question set.

Which of the following is an abiotic component of an ecosystem?

A. Producers
B. Decomposers
C. Temperature ✓
D. Consumers

Answer: C. Temperature
Abiotic components are non-living factors such as temperature, light, water and soil. Producers, consumers and decomposers are biotic components.

The vertical distribution of different species occupying different levels in an ecosystem is called:

A. Stratification ✓
B. Decomposition
C. Mineralisation
D. Leaching

Answer: A. Stratification
Stratification refers to the vertical layering of organisms, such as trees, shrubs and herbs in a forest ecosystem.

Gross primary productivity is the rate of production of organic matter by producers during:

A. Respiration
B. Photosynthesis ✓
C. Decomposition
D. Mineral cycling

Answer: B. Photosynthesis
Gross primary productivity is the total organic matter produced by plants during photosynthesis per unit area per unit time.

Fill in the blank: Net primary productivity is equal to gross primary productivity minus ________.

A. Respiration loss ✓
B. Leaching loss
C. Mineralisation
D. Standing crop

Answer: A. Respiration loss
Net primary productivity is calculated as NPP = GPP - R, where R is respiration loss.

If the gross primary productivity of an ecosystem is 1200 kcal m−2 yr−1 and respiration loss is 500 kcal m−2 yr−1, what is its net primary productivity?

A. 500 kcal m−2 yr−1
B. 700 kcal m−2 yr−1 ✓
C. 1200 kcal m−2 yr−1
D. 1700 kcal m−2 yr−1

Answer: B. 700 kcal m−2 yr−1
NPP = GPP - R. Therefore, NPP = 1200 - 500 = 700 kcal m−2 yr−1.

Which of the following best describes a food web?

A. A single straight pathway of energy flow
B. A network of interconnected food chains ✓
C. Only the feeding relation between producers and decomposers
D. A diagram showing only biomass at each trophic level

Answer: B. A network of interconnected food chains
A food web is formed by interconnection of several food chains, providing alternate pathways of energy flow.

A forest has many plant layers such as tall trees, smaller trees, shrubs and herbs. This is an example of:

A. Nutrient leaching
B. Stratification ✓
C. Humification
D. Energy loss

Answer: B. Stratification
Vertical layering of vegetation in a forest is called stratification, a structural feature of ecosystems.

If an ecosystem receives 1,000,000 J of solar energy and producers fix 1 percent of it, how much energy will be available to secondary consumers according to the 10 percent law?

A. 10 J
B. 100 J ✓
C. 1,000 J
D. 10,000 J

Answer: B. 100 J
Producers fix 1 percent of 1,000,000 J = 10,000 J. Herbivores get 1,000 J and secondary consumers get 100 J.

Which statement about the carbon cycle and phosphorus cycle is correct?

A. Both have atmosphere as their main reservoir
B. Carbon cycle is sedimentary and phosphorus cycle is gaseous
C. Carbon has a major atmospheric component, while phosphorus mainly cycles through rocks and sediments ✓
D. Phosphorus is released in large amounts through respiration like carbon dioxide

Answer: C. Carbon has a major atmospheric component, while phosphorus mainly cycles through rocks and sediments
Carbon cycling involves the atmosphere mainly as carbon dioxide, while phosphorus has its major reservoir in rocks and sediments.

Consider the sequence: detritus → humus → inorganic nutrients. Which option correctly represents the processes mainly responsible for these changes?

A. Fragmentation followed by photosynthesis
B. Humification followed by mineralisation ✓
C. Leaching followed by stratification
D. Primary productivity followed by respiration

Answer: B. Humification followed by mineralisation
Humification leads to the formation of humus from detritus, and mineralisation releases inorganic nutrients from humus.

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