CBSE Class 12 Biology Case-Based Questions – Ecosystem (NCERT Based)

Unit V: Ecology and Environment | Chapter 14: Ecosystem

CBSE Class 12 Biology Chapter 14 Case-Based Questions – Ecosystem (NCERT)

Course & Examination Details

• Course: CBSE Class 12 Biology
• Unit: Unit V – Ecology and Environment
• Chapter: Chapter 14 – Ecosystem
• Board: Central Board of Secondary Education (CBSE)
• Syllabus Base: Strictly as per NCERT Textbook
• Exam Relevance: CBSE Class 12 Board Examinations (Competency-Based / Case-Based Questions)

Case-Based Questions with Answers

(Prepared strictly according to NCERT content and the latest CBSE competency-based assessment pattern)

Section A: Ecosystem Structure and Function (Case 1–5)

Case 1

A pond contains green plants, fishes, insects, microorganisms, water, nutrients, and sunlight.

Q1. Identify the type of ecosystem.
Ans: It is a natural aquatic ecosystem.

Q2. Name the producers in this ecosystem.
Ans: Green plants and algae act as producers.

Case 2

An ecosystem shows interaction between living organisms and physical factors like light, temperature, and water.

Q1. Name the two major components of an ecosystem.
Ans: Biotic and abiotic components.

Q2. How are these components connected?
Ans: They are connected through energy flow and nutrient cycling.

Case 3

Crop fields require irrigation, fertilizers, and human care for productivity.

Q1. What type of ecosystem is this?
Ans: Artificial ecosystem.

Q2. Why is it not self-sustaining?
Ans: It depends on continuous human inputs.

Case 4

Microorganisms break down dead plants and animals in soil.

Q1. What group of organisms performs this function?
Ans: Decomposers.

Q2. Why are they important?
Ans: They recycle nutrients and maintain soil fertility.

Case 5

An ecosystem continues to function due to constant solar input.

Q1. What type of system is an ecosystem?
Ans: Open system.

Q2. What is the main source of energy?
Ans: Sunlight.

Section B: Productivity (Case 6–10)

Case 6

Plants convert solar energy into chemical energy during photosynthesis.

Q1. What type of productivity is this?
Ans: Primary productivity.

Q2. Name the organisms responsible.
Ans: Producers.

Case 7

A part of energy fixed by plants is used for respiration.

Q1. What is the total energy fixed called?
Ans: Gross Primary Productivity (GPP).

Q2. What remains after respiratory loss?
Ans: Net Primary Productivity (NPP).

Case 8

Herbivores grow by consuming plant biomass.

Q1. What is this productivity called?
Ans: Secondary productivity.

Q2. On what does it depend?
Ans: Availability of primary productivity.

Case 9

Tropical forests show higher biomass production.

Q1. Why is productivity high in tropical regions?
Ans: Due to high sunlight, temperature, and rainfall.

Q2. Name one tropical ecosystem.
Ans: Tropical rainforest.

Case 10

Aquatic ecosystems show low producer biomass but high productivity.

Q1. Why is biomass low in aquatic producers?
Ans: Producers like phytoplankton have short life spans.

Q2. How is productivity still high?
Ans: Due to rapid turnover rates.

Section C: Decomposition (Case 11–15)

Case 11

Dead leaves fall on forest floor and break down over time.

Q1. Name the process involved.
Ans: Decomposition.

Q2. Name one organism involved.
Ans: Bacteria or fungi.

Case 12

Earthworms break detritus into smaller particles.

Q1. Name this step of decomposition.
Ans: Fragmentation.

Q2. What organisms perform it?
Ans: Detritivores.

Case 13

Soluble nutrients move downward into soil layers.

Q1. Identify this step.
Ans: Leaching.

Q2. What does it transport?
Ans: Water-soluble nutrients.

Case 14

Dark, amorphous organic matter accumulates in soil.

Q1. What is it called?
Ans: Humus.

Q2. Name the process forming it.
Ans: Humification.

Case 15

Inorganic nutrients become available for plant uptake.

Q1. Name this final step of decomposition.
Ans: Mineralisation.

Q2. Why is it important?
Ans: It supports plant growth.

Section D: Energy Flow and Ecological Pyramids (Case 16–20)

Case 16

Energy moves from plants to herbivores to carnivores.

Q1. What does this sequence represent?
Ans: Food chain.

Q2. What type of energy flow occurs?
Ans: Unidirectional.

Case 17

Only a small fraction of energy reaches higher trophic levels.

Q1. Name the law explaining this.
Ans: Ten percent law.

Q2. Where is energy lost?
Ans: As heat during metabolism.

Case 18

An aquatic ecosystem shows less producer biomass than consumers.

Q1. Which pyramid is inverted here?
Ans: Pyramid of biomass.

Q2. Why does this happen?
Ans: Due to rapid turnover of phytoplankton.

Case 19

Energy pyramid is always upright.

Q1. Why is it always upright?
Ans: Energy decreases at each trophic level.

Q2. Which pyramid best shows ecosystem functioning?
Ans: Pyramid of energy.

Case 20

Multiple food chains are interconnected in a grassland.

Q1. What is this network called?
Ans: Food web.

Q2. What advantage does it provide?
Ans: Greater ecosystem stability.

Section E: Nutrient Cycles, Succession & Ecosystem Services (Case 21–25)

Case 21

Carbon dioxide is fixed by plants and released by respiration.

Q1. Name this nutrient cycle.
Ans: Carbon cycle.

Q2. Name one process releasing CO₂.
Ans: Respiration.

Case 22

Nitrogen gas is converted into ammonia by bacteria.

Q1. Name this process.
Ans: Nitrogen fixation.

Q2. Why is nitrogen important?
Ans: It is required for proteins and nucleic acids.

Case 23

Plants colonize bare rocks after volcanic eruption.

Q1. What type of succession is this?
Ans: Primary succession.

Q2. Why is it slow?
Ans: Due to absence of soil.

Case 24

Grass grows after forest fire in an area.

Q1. Identify the type of succession.
Ans: Secondary succession.

Q2. Why is it faster?
Ans: Soil and nutrients are already present.

Case 25

Forests provide food, regulate climate, and prevent floods.

Q1. What are these benefits called?
Ans: Ecosystem services.

Q2. Name one regulating service.
Ans: Climate regulation.

CBSE Exam Note

These case-based questions are designed to strengthen application skills, analytical thinking, and conceptual understanding, fully aligned with NCERT Chapter 14 – Ecosystem and the CBSE competency-based exam pattern.