NCERT Solutions Class 8 Science Chapter 12 2026-27 PDF

Concept used. The order is individual, population, community and ecosystem. A community is made of different populations. An ecosystem includes the community plus abiotic components. Statement (iii) is wrong. A community is part of an ecosystem, not the other way round.

1. A population is a group of the same kind of organisms living in one habitat at a given time.
2. A community includes different populations living together in the same habitat.
3. An ecosystem includes the community and abiotic components such as air, water, soil, sunlight and temperature.
4. So a community is larger than a population.
5. A community is smaller than an ecosystem.
6. Therefore statement (iii), an ecosystem is part of a community, is wrong.

Concept used. Decomposers such as bacteria and fungi break down dead matter and return nutrients to soil. They keep nutrient cycling active. Dead matter and waste would pile up, soil nutrients would fall, plant growth would reduce, and the whole food web would be disturbed.

1. Decomposers break down dead plants, dead animals, dung and fallen leaves.
2. This breakdown returns nutrients to the soil.
3. If decomposers disappear, dead matter and waste will accumulate.
4. Soil will slowly lose usable nutrients because nutrients will remain locked in dead matter.
5. Plants will grow poorly in nutrient-poor soil.
6. Fewer plants will reduce food and shelter for herbivores and then for carnivores.
7. Thus decomposers are essential for recycling nutrients and maintaining ecosystem balance.

Concept used. Mangroves are coastal forests with dense roots. They reduce the force of waves, trap sediments and protect coastlines during storms and floods. Yes. Mangrove forests act as natural barriers. Their roots and trunks slow waves, reduce erosion and absorb part of the impact.

1. Mangroves grow along coasts and river mouths.
2. Their tangled roots and thick vegetation form a living barrier.
3. When strong waves reach mangroves, the roots and stems slow the water flow.
4. This reduces the force of waves reaching villages behind them.
5. Mangroves also hold soil and reduce coastal erosion.
6. So Selvam's village may have been less affected because the mangrove forest reduced the impact of tsunami waves.

Concept used. In a food chain, each organism depends on the previous organism for food and may be eaten by the next organism. Grasshoppers will increase because fewer frogs eat them. Snakes will decrease because they lose frogs as food.

1. In this food chain, frogs eat grasshoppers.
2. If frogs disappear, predation on grasshoppers reduces.
3. So the grasshopper population is likely to increase.
4. Snakes feed on frogs in this chain.
5. If frogs are absent, snakes get less food.
6. So the snake population is likely to decrease or move elsewhere.

Concept used. Butterflies need flowering plants, host plants for larvae, safe shelter and low pesticide exposure. Their number changes when these habitat needs change. Possible reasons are fewer flowers, loss of host plants, pesticide use, pollution, dry weather or habitat disturbance. Students can plant native flowers and host plants and avoid pesticides.

1. Butterflies visit flowers for nectar.
2. If flowering plants are fewer, butterflies get less food.
3. Their larvae need specific host plants, so loss of these plants reduces butterfly numbers.
4. Pesticides can kill butterflies, caterpillars and other helpful insects.
5. Extreme heat, less water, pollution or garden disturbance can also reduce them.
6. Students can plant native flowering plants in different seasons.
7. They can also plant host plants, keep a small water source, avoid pesticides and protect garden corners from trampling.

Concept used. An ecosystem needs producers, consumers and decomposers for energy flow, population balance and nutrient recycling. Only producers cannot keep an ecosystem balanced. Consumers transfer energy and control populations, while decomposers recycle nutrients from dead matter.

1. Producers make food using sunlight, water and carbon dioxide.
2. Consumers feed on producers or other consumers, so energy moves through the food chain.
3. Consumers also help keep some populations from growing without limit.
4. All organisms eventually produce waste and die.
5. Decomposers break down this dead matter and return nutrients to the soil.
6. Without consumers and decomposers, energy flow and nutrient recycling are incomplete.
7. So a stable ecosystem cannot have only producers.

Concept used. Biotic components are living organisms. Abiotic components are non-living things such as light, air, water, soil, temperature and stones. A park may have trees, grass, birds, insects, soil, water and shade. A roadside may have weeds, ants, dust, stones, vehicles, heat and less soil moisture.

1. In a park, biotic components may include trees, grass, shrubs, birds, ants, butterflies and soil microbes.
2. Park abiotic components may include soil, water, sunlight, air, rocks and shade.
3. On a roadside, biotic components may include weeds, small grasses, ants, stray animals and some insects.
4. Roadside abiotic components may include dust, tar road, stones, air, heat, sunlight and little water.
5. The park usually has more plant cover, more shade, more soil moisture and more animals.
6. The roadside usually has more disturbance, pollution, heat and less biodiversity.

Concept used. Human-made ecosystems such as farms provide food and livelihoods, but they need careful management to protect soil, water, biodiversity and human health. Agricultural fields are necessary for food, but overuse of fertilisers, pesticides, water and monoculture can damage soil and biodiversity. Sustainable practices reduce harm.

1. Farms are human-made ecosystems because humans create and manage them for crop production.
2. They are necessary because they provide food, fibres and livelihoods.
3. But unsustainable farming can overuse synthetic fertilisers, pesticides and groundwater.
4. These practices may reduce soil fertility, harm friendly organisms and pollute water.
5. Growing the same crop repeatedly can reduce biodiversity and affect pollinators.
6. Sustainable farming uses compost, crop rotation, mixed cropping, natural pest control, careful irrigation and less chemical use.
7. So farms are necessary, but they should be managed in an eco-friendly way.

Concept used. In the shown food web, grasses and plants feed hare and deer. Hare is prey for fox. Changes in one population can affect other linked populations. Foxes may decrease or shift to other prey because they get fewer hares. Grass and plants may increase because fewer hares eat them. Other links may also change.

1. In Fig. 12.20, hare feeds on grass and plants.
2. If hare population drops, less grass and plant material is eaten by hares.
3. So grasses and plants may increase, if other herbivores do not consume them equally.
4. The fox depends on hare as a food source in the shown web.
5. With fewer hares, foxes may get less food.
6. Fox numbers may decrease, or foxes may hunt other prey if available.
7. Other organisms linked through the web may also change because food webs are interconnected.