Looking for authentic, 100% textbook-grounded NCERT Solutions for Class 8 Science Chapter 12: How Nature Works in Harmony (Curiosity, 2026-27 CBSE Curriculum)? Below is the complete Topper’s Handwritten Style solutions notebook covering every single exercise, numerical problem, and reflective inquiry question directly from the official NCERT textbook.
Chapter Overview: How Nature Works in Harmony
NCERT Class 8 Science Chapter 12 explores ecosystem ecology, trophic dynamics, and nature’s interconnectedness. Students learn the ecological hierarchy (Organism → Population → Community → Ecosystem), food chains and food webs, the vital role of decomposers in nutrient cycling, and case studies including mangrove wetlands shielding coastlines during tsunamis.
Subject: Class 8 Science (Curiosity)
Chapter: 12 — How Nature Works in Harmony
Target: 100/100 CBSE Exam Prep
Topper’s Handwritten Notebook Solutions (Revise, Reflect, Refine)
Question 1: Refer to the ecological hierarchy diagram (Organism → Population → Community → Ecosystem). Select the WRONG statement and justify: (i) A community is larger than a population. (ii) A community is smaller than an ecosystem. (iii) An ecosystem is part of a community.
Step 1: Ecological Hierarchy Definitions
- Organism: An individual living entity (e.g., one deer).
- Population: A group of individuals of the same species living in a specific area (e.g., all deer in a forest).
- Community: All the interacting populations of different species inhabiting an area (e.g., deer + tigers + trees + grass + birds).
- Ecosystem: The biological community interacting with all the non-living physical components (abiotic factors: soil, air, water, sunlight, temperature).
Step 2: Identifying the Wrong Statement
Statement (i) is correct: A community contains multiple populations.
Statement (ii) is correct: Ecosystem includes community plus abiotic physical factors.
Statement (iii) is WRONG: An ecosystem is NOT part of a community; rather, a community is part of an ecosystem!
Statement (ii) is correct: Ecosystem includes community plus abiotic physical factors.
Statement (iii) is WRONG: An ecosystem is NOT part of a community; rather, a community is part of an ecosystem!
Wrong Statement: (iii) An ecosystem is part of a community. Justification: Ecosystem is the broader ecological level containing both the biotic community and abiotic physical environment.
💡 Hierarchy Chain: Organism → Population → Community → Ecosystem → Biome → Biosphere.
Question 2: If all decomposers (bacteria and fungi) suddenly disappeared from a forest ecosystem, what catastrophic changes would occur? Explain why decomposers are indispensable.
Step 1: Primary Function of Decomposers
Decomposers are saprophytic microorganisms (bacteria, molds, fungi) that secrete extracellular enzymes to break down complex organic compounds in dead plant matter (fallen leaves, rotting logs) and animal carcasses into simple inorganic nutrients (nitrogen, phosphorus, potassium, carbon).
Step 2: Consequences of Decomposer Disappearance
- Accumulation of Dead Organic Waste: Mountains of dead tree trunks, animal corpses, and leaf litter would pile up indefinitely without decomposing, choking the forest floor.
- Halting of Biogeochemical Cycles: Essential nutrients (N, P, K) locked in dead biomass would never return to the soil.
- Soil Infertility and Plant Death: Depleted of mineral nutrients, plants (producers) would fail to grow and synthesize food.
- Trophic Collapse: Herbivores would starve, leading to extinction of carnivores. The entire ecosystem would collapse!
Conclusion: Without decomposers, nutrient recycling ceases, dead waste accumulates uncontrollably, soil fertility vanishes, and all food chains collapse entirely.
💡 Nature’s Scavengers: Decomposers are the ultimate recyclers that maintain Earth’s circular nutrient economy.
Question 3: Selvam from Cuddalore district, Tamil Nadu, shared that his village was significantly less affected by the catastrophic 2004 Indian Ocean Tsunami compared to nearby villages due to mangrove forests. Explain how mangroves protect coastal villages.
Step 1: Unique Morphology of Mangroves (Rhizophora / Avicennia)
Mangrove trees grow in saline coastal intertidal zones. They develop dense networks of specialized, stilted prop roots and stilt roots that intertwine tightly above and below water, along with vertical breathing roots (pneumatophores).
Step 2: Tsunami & Cyclone Wave Dissipation Mechanism
- Kinetic Energy Absorption: When colossal tsunami waves or storm surges crash into the coastline, the dense labyrinth of mangrove roots acts as a powerful porous sea wall. The roots break up the surge, frictionally absorbing and dissipating over 60% – 70% of the wave’s destructive kinetic energy!
- Soil Stabilization: Mangrove roots bind coastal sediments firmly, preventing devastating soil erosion and land collapse.
- Windbreak Function: Dense mangrove canopies reduce howling maritime cyclonic winds, shielding village homes behind them.
Summary: Dense mangrove prop root networks act as natural shock-absorbing bio-shields that dissipate wave kinetic energy, stabilize soil, and prevent catastrophic coastal inundation.
💡 Ecological Term: Mangrove forests are vital ‘Bio-Shields’ and coastal nurseries for marine life.
📌 Master Exam Revision Checklist for Chapter 12
- Ecological Hierarchy: Individual → Population (same species) → Community (all species) → Ecosystem (Biotic + Abiotic).
- Role of Decomposers: Decompose dead organic matter, replenish soil nutrients, and drive circular biochemical cycles.
- Mangrove Bio-Shields: Prop roots frictionally absorb tsunami and storm wave energy, protecting coastal human settlements.