Our Environment | Science Grade 8 CBSE

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The six ideas behind an ecosystem

Who makes the food, who eats it, who recycles it — and how do we keep the whole system healthy? These six terms explain how the living world fits together. Tap each one to find out what it means.

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The three big ideas

The environment is everything around us: the biotic (living) parts — plants, animals, microbes — and the abiotic (non-living) parts — sunlight, air, water, soil and temperature.
An ecosystem is a community of living organisms interacting with each other and with their non-living surroundings in a particular area. A pond, a forest, a grassland and a desert are all ecosystems — they can be as small as a rotting log or as large as a whole forest.
Living things play three roles: producers (green plants — make food by photosynthesis), consumers (animals — herbivores, carnivores, omnivores) and decomposers (bacteria and fungi — the recyclers).
All three groups depend on one another and on the abiotic factors around them.

Worked example. Identify the roles in a pond ecosystem.

Algae and water plants are the producers; small fish and insects are the consumers; bacteria on the pond bottom are the decomposers. Together with the water and sunlight (abiotic), they form one ecosystem.

A food chain shows who-eats-whom, e.g. grass → grasshopper → frog → snake → eagle. Each step is a trophic level.
Energy enters as sunlight, is captured by producers, and passes up the chain. Only a small part (about one-tenth) reaches the next level, so chains are short and there are fewer animals at the top.
Energy flows in one direction and is not recycled — but nutrients (matter) are recycled by decomposers, back into the soil.
A food web is many food chains linked together. Because most animals eat more than one kind of food, the chains interconnect — which makes the ecosystem more stable.

Worked example. In grass → grasshopper → frog → snake → eagle, what happens if all the frogs disappear?

With no frogs eating them, grasshoppers increase (and may damage the grass), while snakes go hungry because they lose their food. Removing one link disturbs the whole web.

Common mistake: starting a food chain with an animal. A food chain always begins with a producer (a green plant), because that is where the energy first enters the living world.

Pollution is harmful substances added to air, water or soil — vehicle and factory smoke (air), sewage and plastics (water), chemicals and non-degradable waste (soil). Its effects include disease, dirty water, dying fish and a changing climate.
Biodiversity is the variety of living things. A rich variety keeps ecosystems healthy. Loss of habitat and over-hunting can make a species endangered or even extinct.
Conservation protects forests and wildlife: national parks, wildlife sanctuaries and biosphere reserves; planting trees (afforestation); the 3 Rs — reduce, reuse, recycle; saving water and energy; avoiding single-use plastic.
In India, conservation efforts include Project Tiger, and protected homes for the one-horned rhino (Kaziranga) and the Asiatic lion (Gir).

Worked example. Name three simple daily actions that protect an ecosystem.

Plant native trees, separate your waste so it can be composted or recycled, and never litter rivers or ponds. Small everyday choices add up to real conservation.

Common mistake: assuming all waste rots away. Most plastics are non-biodegradable — they do not decompose and pile up, harming soil, water and animals for decades.

Where you'll meet it

The environment around you

A garden pond

A small pond is a complete ecosystem: water plants make food, fish and insects eat and are eaten, and microbes recycle the waste — all powered by sunlight.

Why frogs and vultures matter

Lose the scavengers and predators, and dead matter piles up or pests multiply. Every species — even an unglamorous one — has a job in the food web.

Waste segregation at home

Separating wet (compostable) waste from dry (recyclable) waste turns a pollution problem into reused resources — conservation that starts in your own kitchen.

Check yourself

Competency quiz

Modelled on the competency-based pattern — MCQ, assertion–reason and a case study, testing whether you can use the ideas, not just recall them.

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