NCERT Solutions for Class 8 Science Curiosity Chapter 12 How Nature Works in Harmony

1. Refer to the given diagram (Fig. 12.19) and select the wrong statement.
(i) A community is larger than a population.
(ii) A community is smaller than an ecosystem.
(iii) An ecosystem is part of a community.

See Answer(iii) An ecosystem is part of a community.
This is wrong because a community is part of an ecosystem, not the other way around. An ecosystem = community (biotic) + abiotic components.

2. A population is part of a community. If all decomposers suddenly disappear from a forest ecosystem, what changes do you think would occur? Explain why decomposers are essential.
See AnswerIf decomposers disappear:
• Dead plants and animals will accumulate.
• Nutrients will not be recycled back to the soil.
• Soil fertility will decrease, and plants will not get essential nutrients.
• This will disturb the entire food chain and ecosystem balance.
Decomposers are essential because they recycle nutrients and keep nature’s cycle running.

3. Selvam from Cuddalore district, Tamil Nadu, shared that his village was less affected by the 2004 Tsunami compared to nearby villages due to the presence of mangrove forests. This surprised Sarita, Shabnam, and Shijo. They wondered if mangroves were protecting the village. Can you help them understand this?
See AnswerYes.
• Mangroves act as a natural barrier.
• They slow down strong winds and waves during storms and tsunamis.
• Their roots hold the soil and prevent coastal erosion.
Thus, mangroves protect human settlements from disasters.

4. Look at this food chain:
Grass → Grasshopper → Frog → Snake
If frogs disappear from this ecosystem, what will happen to the population of grasshoppers and snakes? Why?
See AnswerGrasshoppers will increase (because no frogs to eat them). Snakes will decrease (because they lose their food source – frogs). This imbalance will disturb the food chain.

5. In a school garden, students noticed fewer butterflies the previous season. What could be the possible reasons? What steps can students take to have more butterflies on campus?
See AnswerPossible reasons:
• Fewer flowering plants (less nectar).
• Use of pesticides harming insects.
• Climate or habitat changes.
Steps students can take:
• Grow more flowering plants.
• Avoid use of chemical pesticides.
• Maintain a clean and natural habitat for butterflies.

6. Why is it not possible to have an ecosystem with only producers and no consumers or decomposers?
See Answer• Producers (plants) make food, but without consumers no one would use that food.
• Without decomposers, dead matter would pile up and nutrients would not recycle.
Therefore, all three (producers, consumers, decomposers) are necessary for balance in an ecosystem.

7. Observe two different places near your home or school (e.g., a park and a roadside). List the living and non-living components you see. How are the two ecosystems different?
See AnswerPark ecosystem:
• Living: trees, grass, birds, insects, squirrels.
• Non-living: soil, water, sunlight, air.
Roadside ecosystem:
• Living: few plants, stray dogs, crows, ants.
• Non-living: concrete, dust, vehicles, heat.
Difference:
• Park has more biodiversity and balance.
• Roadside has less greenery and more pollution.

8. ‘Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable.’ Comment on the statement.
See Answer• Human-made ecosystems like farms give us food and resources.
• But unsustainable practices (excess pesticides, monoculture, overuse of water) harm soil, health and environment.
To make them sustainable:
• Use organic/natural farming.
• Practice crop rotation.
• Conserve water and soil.
Thus, we need sustainable farming for future food security.

9. If the Indian hare population (Fig. 12.20) drops because of a disease, how would it affect the number of other organisms?

See Answer• Grass and plants will increase (less eaten by hares).
• Predators of hare (fox, eagle) will decrease due to lack of food.
• Other prey animals (like deer or mice) may face more pressure as predators shift to them.
This shows how one change affects the whole food web.