NCERT Curiosity · Class 8 · Science
How Nature Works in Harmony
Elephants wander into farms and villages when their forest habitat shrinks. What does this reveal about how closely everything in nature is connected?
Key idea
Habitats: Biotic and Abiotic
1
Biotic components
The living things in a habitat — plants, animals, and microbes.
→
2
Abiotic components
The non-living things — air, water, soil, temperature, and sunlight.
Key idea
Population and Community
1
Population
A group of organisms of the same kind, living together in a habitat.
→
2
Community
All the different populations sharing the same habitat, interacting and depending on each other.
Key idea
Ecosystems in Action
In a pond study: fish reduce dragonfly larvae, which lets more pollinators (bees, butterflies) survive, which increases seed production nearby.
The whole interacting system of biotic and abiotic components in a habitat — one small change can ripple through many others.
Key idea
Producers, Consumers, and Decomposers
1
Producers
Make their own food via photosynthesis — green plants.
→
2
Consumers
Depend on others for food — herbivores, carnivores, omnivores.
→
3
Decomposers
Break down dead matter, recycling nutrients — fungi, bacteria.
Key idea
A Food Chain
Grass → Grasshopper → Frog → Snake → Eagle
Key idea
Trophic Levels
The number of organisms typically decreases going up each level — forming a pyramid shape.
Key idea
Food Webs
Food web. Real ecosystems rarely have just one food chain — many chains interlink into a network, because most animals eat (and are eaten by) more than one other kind.
Key idea
Mutualism, Commensalism, and Parasitism
Relationship | Who benefits | Example
MutualismBoth organisms — Honeybees and flowers
CommensalismOne; the other unaffected — Orchids growing on trees
ParasitismOne; the other harmed — Ticks on dogs
Key idea
When One Change Cascades
Pollution killing pond plants → less oxygen → fish die → fewer consumers → more insects → pesticide use → further harm.
Competition for food, water, space, and sunlight normally keeps populations in check — but one disruption can set off a chain reaction.
Key idea
Ecosystem Benefits: The Sundarbans
Ecosystems give us fresh air, fertile soil, food, timber, medicines, and recreational value.
The world's largest mangrove forestThe Sundarbans protects coastlines from storms and absorbs CO2 — but faces threats from logging, hunting, and pollution.
Key idea
The Green Revolution and Monoculture
1
The Green Revolution
Boosted food production in the 1950s–60s using tractors, fertilisers, and pesticides — but overuse now causes soil degradation and biodiversity loss.
→
2
Monoculture
Growing the same crop repeatedly reduces biodiversity and harms the pollinators that ecosystems depend on.
Chapter · Key terms to remember
Key Terms
Habitat
The place providing conditions for an organism to live.
Population / Community
Same species / all species sharing a habitat.
Ecosystem
Biotic and abiotic components interacting.
Chapter · Key terms to remember
More Key Terms
Producers / Consumers / Decomposers
Make food / eat others / recycle waste.
Food chain / web
Who eats whom / interlinked food chains.
Trophic level
An organism's feeding position in a food chain.
Chapter · Key terms to remember
More Key Terms
Mutualism / Commensalism / Parasitism
Both benefit / one benefits / one harmed.
Monoculture
Growing the same crop repeatedly.
Questions for your notebook
Write these down, then discuss
1Looking at a nested diagram of population, community, and ecosystem, which statement is wrong: (i) A community is larger than a population. (ii) A community is smaller than an ecosystem. (iii) An ecosystem is part of a community.
2If all decomposers suddenly disappeared from a forest ecosystem, what would happen? Why are decomposers essential?
3Selvam's village in Cuddalore was less damaged by the 2004 Tsunami than nearby villages, thanks to mangrove forests. How might mangroves have protected the village?
Project as-is — students copy the questions, then the class discusses answers together.