Solutions For All Chapters – Science Class 8
How Nature Works in Harmony
Keep the curiosity alive
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 community.
Answer:- (iii) An ecosystem is part of a community.
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.
Answer:- If all decomposers suddenly disappear from a forest ecosystem, dead plants and animals would not break down, causing a buildup of waste and dead matter. This would reduce soil nutrients, making it harder for plants to grow, which could lead to a decline in plant and animal populations. Decomposers are essential because they break down complex substances in dead matter into simpler ones, recycling nutrients back into the soil to support plant growth and maintain the ecosystem’s balance.
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?
Answer:- Yes. Mangroves act as a natural barrier. Their thick roots and dense trees slow down strong waves, reduce flooding, and prevent soil erosion. That is why villages with mangroves are protected.
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?
Answer:- If frogs disappear, the population of grasshoppers will increase because no frogs will eat them. The population of snakes will decrease because they will lose their food source (frogs). Thus, the balance of the food chain will be disturbed.
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?
Answer:-
Possible reasons for fewer butterflies:
- Fewer flowering plants, which means less nectar for butterflies.
- Use of pesticides that may harm butterflies or their larvae.
- Pollution or loss of natural plants and shelter in the garden.
- Changes in weather or climate affecting butterfly visits.
Steps students can take:
- Plant more colorful, nectar-rich flowers that attract butterflies.
- Avoid using harmful chemicals or pesticides in the garden.
- Create a butterfly-friendly space with shade, water, and native plants.
- Spread awareness among students about protecting butterfly habitats.
6. Why is it not possible to have an ecosystem with only producers and no consumers or decomposers?
Answer:- It is not possible to have an ecosystem with only producers because consumers and decomposers are also needed.
- Consumers eat the plants and keep their number in balance.
- Decomposers break down dead plants and animals and return nutrients to the soil.
Without consumers and decomposers, plants would overgrow, dead matter would accumulate, and nutrients would not recycle. Thus, the balance of the ecosystem would be lost.
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?
Answer:-
1. Park ecosystem:
- Living components – trees, grass, birds, insects, small animals.
- Non-living components – soil, water, sunlight, air.
2. Roadside ecosystem:
- Living components – a few shrubs, stray animals, very few plants.
- Non-living components – dust, smoke, vehicles, heat, air.
Difference: The park has more greenery, biodiversity, and fresh air, while the roadside has less vegetation, more pollution, and fewer living organisms.
8. ‘Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable.’ Comment on the statement
Answer:- Human-made ecosystems like agricultural fields are necessary because they provide food and other useful products for humans. But if too many chemicals, pesticides, and water are used, the soil and environment get damaged.
To make them sustainable, farmers should use eco-friendly methods such as natural manures, crop rotation, less water wastage, and avoiding harmful chemicals. This keeps the soil healthy and the ecosystem balanced.
9. If the Indian hare population (Fig. 12.20) drops because of a disease, how would it affect the number of other organisms?
Answer:- If the Indian hare population decreases, animals that feed on it like foxes and eagles will get less food, so their numbers will also decrease. At the same time, the plants and grass eaten by hares will increase because fewer hares will feed on them. Thus, the balance of the food web will be disturbed.
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