CBSE Class 12 Biology Short Answer Questions – Ecosystem (NCERT Based)

Unit V: Ecology and Environment | Chapter 14: Ecosystem

CBSE Class 12 Biology Chapter 14 Short Answer 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 (2–3 mark questions)

Short Answer Type Questions (60–80 Words Each)

(Prepared strictly as per NCERT concepts and CBSE answer-writing standards)

Section A: Ecosystem – Structure and Function (Q1–Q8)

Q1. Define an ecosystem and mention its main components.
Ans: An ecosystem is a functional unit of nature where living organisms interact with each other and with the physical environment. It consists of biotic components such as producers, consumers, and decomposers, and abiotic components like light, water, temperature, soil, and nutrients. These components are interconnected through energy flow and nutrient cycling.

Q2. Distinguish between biotic and abiotic components of an ecosystem.
Ans: Biotic components include all living organisms such as plants, animals, and microorganisms, which interact and depend on each other. Abiotic components are non-living factors like light, temperature, water, air, and soil that influence the survival, growth, and distribution of organisms within the ecosystem.

Q3. Explain the role of producers in an ecosystem.
Ans: Producers are autotrophic organisms, mainly green plants, that synthesize organic food from inorganic substances using sunlight through photosynthesis. They form the base of all food chains and are the primary source of energy for consumers. Without producers, energy would not enter the ecosystem.

Q4. Who are decomposers and why are they important?
Ans: Decomposers are microorganisms such as bacteria and fungi that break down dead plants and animals into simpler inorganic substances. They recycle nutrients back into the soil, making them available for producers, thereby maintaining nutrient balance and ecosystem stability.

Q5. What are the major functional aspects of an ecosystem?
Ans: The major functional aspects of an ecosystem include productivity, decomposition, energy flow, and nutrient cycling. These processes ensure the transfer of energy, recycling of nutrients, and continuity of life within the ecosystem.

Q6. Explain why ecosystems are considered self-sustaining units.
Ans: Ecosystems are self-sustaining because energy flows continuously through trophic levels and nutrients are recycled through decomposition and nutrient cycles. This maintains ecological balance and supports life processes without external input, except sunlight.

Q7. Differentiate between natural and artificial ecosystems.
Ans: Natural ecosystems such as forests and ponds develop naturally and are self-regulated. Artificial ecosystems like crop fields and aquariums are created and maintained by humans and require continuous external inputs such as fertilizers and care.

Q8. How do abiotic factors regulate ecosystem functioning?
Ans: Abiotic factors such as temperature, light, water, and soil regulate metabolic activities, productivity, and species distribution. Any change in these factors affects energy flow, nutrient cycling, and overall ecosystem stability.

Section B: Productivity (Q9–Q14)

Q9. What is primary productivity? Distinguish between GPP and NPP.
Ans: Primary productivity is the rate at which producers synthesize organic matter. Gross Primary Productivity (GPP) is the total photosynthetic production, while Net Primary Productivity (NPP) is the energy available after subtracting respiratory losses. NPP supports consumers.

Q10. Why is Net Primary Productivity important in an ecosystem?
Ans: Net Primary Productivity represents the actual biomass available to consumers. It determines the energy flow to higher trophic levels and influences ecosystem carrying capacity and biodiversity.

Q11. Define secondary productivity.
Ans: Secondary productivity is the rate at which consumers convert consumed food into new biomass. It depends on the availability of primary productivity and determines population growth of consumers.

Q12. Name the factors affecting primary productivity.
Ans: Primary productivity is affected by plant species composition, availability of sunlight, temperature, water, nutrient availability, and photosynthetic efficiency of producers.

Q13. Why is productivity higher in tropical ecosystems?
Ans: Tropical ecosystems receive abundant sunlight, warm temperatures, and adequate rainfall throughout the year, creating favorable conditions for continuous photosynthesis and high productivity.

Q14. Compare productivity in terrestrial and aquatic ecosystems.
Ans: Terrestrial ecosystems usually show higher biomass, while aquatic ecosystems have lower producer biomass but high turnover rates, making them highly productive despite smaller standing crops.

Section C: Decomposition (Q15–Q20)

Q15. Define decomposition and mention its importance.
Ans: Decomposition is the breakdown of dead organic matter into simpler inorganic substances by decomposers. It recycles nutrients back into the ecosystem, maintains soil fertility, and supports primary productivity.

Q16. Describe the major steps involved in decomposition.
Ans: Decomposition involves fragmentation, leaching, catabolism, humification, and mineralisation. These steps convert complex organic matter into simpler inorganic nutrients usable by plants.

Q17. What is humification?
Ans: Humification is the process of formation of humus, a dark, amorphous, and partially decomposed organic matter that enhances soil fertility and water-holding capacity.

Q18. What is mineralisation?
Ans: Mineralisation is the final step of decomposition in which inorganic nutrients like nitrogen and phosphorus are released into the soil for reuse by plants.

Q19. How does climate affect decomposition?
Ans: Warm and moist climates favor rapid microbial activity, leading to faster decomposition. Cold or dry conditions slow down decomposition by reducing decomposer efficiency.

Q20. Why is decomposition slower in acidic soils?
Ans: Acidic soils inhibit microbial growth and enzyme activity, reducing the rate of organic matter breakdown.

Section D: Energy Flow and Ecological Pyramids (Q21–Q30)

Q21. Explain energy flow in an ecosystem.
Ans: Energy flows unidirectionally from the sun to producers and then to consumers through food chains. It is lost as heat at each trophic level and cannot be recycled.

Q22. State the ten percent law of energy transfer.
Ans: Only about 10% of energy is transferred from one trophic level to the next, while the remaining energy is lost as heat during metabolic activities.

Q23. Differentiate between food chain and food web.
Ans: A food chain shows a single linear pathway of energy transfer, whereas a food web represents interconnected food chains, providing stability to ecosystems.

Q24. Why is energy pyramid always upright?
Ans: Energy pyramid is always upright because energy decreases at each successive trophic level due to heat loss and metabolic use.

Q25. Explain pyramid of biomass with an example.
Ans: Pyramid of biomass represents biomass at each trophic level. It is upright in forests but inverted in aquatic ecosystems where phytoplankton have less biomass than consumers.

Q26. What does pyramid of number represent?
Ans: Pyramid of number represents the number of individuals at each trophic level, which may be upright or inverted depending on ecosystem structure.

Q27. Why are food webs more stable than food chains?
Ans: Food webs provide alternative pathways for energy flow, reducing dependency on a single food source and increasing ecosystem stability.

Q28. Which trophic level has maximum energy? Why?
Ans: Producers have maximum energy because they directly capture solar energy through photosynthesis.

Q29. Why is energy flow described as unidirectional?
Ans: Energy cannot be recycled back to producers once lost as heat, so it moves in one direction only.

Q30. How does energy flow limit ecosystem size?
Ans: Continuous energy loss at each trophic level restricts the number of trophic levels an ecosystem can support.

Section E: Nutrient Cycles, Succession & Ecosystem Services (Q31–Q50)

Q31. What are nutrient cycles? Name their types.
Ans: Nutrient cycles involve circulation of nutrients between biotic and abiotic components. They are gaseous cycles and sedimentary cycles.

Q32. Explain the carbon cycle briefly.
Ans: Carbon circulates through atmosphere, biosphere, hydrosphere, and lithosphere. Photosynthesis fixes CO₂, while respiration and decomposition release it back.

Q33. Why is nitrogen cycle essential?
Ans: Nitrogen cycle converts atmospheric nitrogen into usable forms essential for proteins and nucleic acids.

Q34. Why does phosphorus cycle lack a gaseous phase?
Ans: Phosphorus is mainly found in rocks and sediments and does not enter the atmosphere in gaseous form.

Q35. Define ecological succession.
Ans: Ecological succession is the gradual and orderly change in species composition in an area over time.

Q36. Differentiate between primary and secondary succession.
Ans: Primary succession occurs on barren land, while secondary succession occurs in areas previously occupied by life.

Q37. What is a climax community?
Ans: A climax community is the stable and self-perpetuating final stage of ecological succession.

Q38. Name the stages of ecological succession.
Ans: Nudation, invasion, competition, reaction, and stabilization are stages of succession.

Q39. Why is secondary succession faster?
Ans: Presence of soil, seeds, and nutrients speeds up secondary succession.

Q40. Define ecosystem services.
Ans: Ecosystem services are benefits humans obtain from ecosystems.

Q41. Name any two provisioning services.
Ans: Food and fresh water are provisioning services.

Q42. What are regulating ecosystem services?
Ans: Services like climate regulation, flood control, and pollination are regulating services.

Q43. Mention one cultural ecosystem service.
Ans: Recreational and aesthetic value of nature.

Q44. Why are ecosystem services economically important?
Ans: They support agriculture, health, climate stability, and livelihoods without monetary cost.

Q45. How does nutrient cycling maintain ecosystem balance?
Ans: It ensures continuous availability of essential elements for living organisms.

Q46. What happens when nutrient cycles are disrupted?
Ans: Ecosystem productivity declines and ecological imbalance occurs.

Q47. How does decomposition support productivity?
Ans: It releases nutrients back into soil, supporting plant growth.

Q48. Why are ecosystems vulnerable to human activities?
Ans: Pollution, deforestation, and overexploitation disturb energy flow and nutrient cycles.

Q49. How does succession restore disturbed ecosystems?
Ans: Succession gradually rebuilds species diversity and ecosystem functions.

Q50. Why is ecosystem conservation important?
Ans: Conservation ensures sustainability, biodiversity protection, and continued ecosystem services for human survival.

CBSE Exam Note

These short answer questions (2–3 marks) are ideal for CBSE board exams, emphasizing NCERT terminology, structured answers, and conceptual clarity.