NCERT Class 8 Science Chapter 12

An ecosystem is a system formed by the interaction of all living organisms (plants, animals, microorganisms) with each other and with the non-living environment (soil, water, air, sunlight) in a given area. Examples include forests, ponds, grasslands, and deserts. NCERT Class 8 Chapter 12 explains how all components work together in harmony.

A food chain is a simple, linear sequence of who eats whom (e.g., grass → grasshopper → frog → snake → eagle). A food web is a more realistic network of multiple interconnected food chains in an ecosystem, showing that most organisms eat and are eaten by more than one species.

Producers (green plants) make food through photosynthesis. Primary consumers (herbivores like deer) eat producers. Secondary consumers (e.g., frogs) eat primary consumers. Tertiary consumers (e.g., eagles) eat secondary consumers. Decomposers (bacteria, fungi) break down dead matter and recycle nutrients back into the soil.

Decomposers (bacteria and fungi) are essential because they break down dead plants and animals into simpler nutrients and return them to the soil. Without decomposers, dead organic matter would accumulate, nutrients would not be recycled, and plants would not get the minerals they need to grow. They complete the nutrient cycle in every ecosystem.

The carbon cycle is the process by which carbon moves between the atmosphere, living organisms, and the environment. Plants absorb CO₂ for photosynthesis. Animals eat plants (carbon passes on). When organisms die, decomposers release CO₂ back to the atmosphere. Carbon is also released through combustion of fossil fuels and volcanic eruptions.

Human activities disturb ecosystems through: deforestation (destroys habitat), pollution (contaminates air, water, soil), overexploitation (overfishing, hunting), introduction of invasive species, and climate change from greenhouse gas emissions. These activities reduce biodiversity, disrupt food webs, and damage the natural services ecosystems provide.