Chapter 12 — How Nature Works in Harmony II Summary II Question Answers II Notes II Class 8 II Curiosity Book II Latest CBSE Notes

 

Chapter 12 — How Nature Works in Harmony

Question Answers

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.

Answer: Option iii
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.

Decomposers are the organisms that help in breaking down and recycle nutrients, back into the environment. If all decomposers (like fungi and bacteria) suddenly disappeared, the ecosystem would face a destruction. Decomposers are nature’s cleaning crew; they break down dead organic matter and return essential nutrients, like nitrogen and phosphorus, back into the soil. Without them:

• Dead plants and animals would pile up, physically taking over the habitat.
• The soil would quickly become nutrient-poor because the recycling process has stopped.
• Producers (plants) would eventually die off because they lack the minerals needed to grow, leading to the starvation of all other living beings in the forest.

Decomposers are important because they recycle nutrients back into the soil, helping new plants and animals grow.

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?

The story of Selvam’s village in Cuddalore highlights the incredible protective power of mangrove forests. Mangroves act as a bio-shield during natural disasters like the 2004 Tsunami. They protect us by:

i.         Their dense, tangled root systems (called pneumatophores) break the force of waves, slowing down the water before it reaches the land.

ii.         Mangrove roots hold the soil firmly in place, preventing the coastline from being washed away by the strong sea waves.

iii.         The thick canopy of trees acts as a windbreak, reducing the impact of storm and high winds.

Mangroves are one of the most effective natural defenses we have against the power of the ocean.

4.Look at this food chain:  Grass à Grasshopper à Frog à Snake

If frogs disappear from this ecosystem, what will happen to the population of grasshoppers and snakes? Why?

Considering the food chain: Grass → Grasshopper → Frog → Snake → Eagle. If the frog population were to disappear, This will disrupt the Food Chain and lasting impact would occur throughout the ecosystem:

The Grasshoppers population would increase rapidly because their primary predator (the frog) is gone. This could lead to overgrazing, where grasshoppers eat all the grass, eventually destroying the producers.

The Snakes population would decrease because they have lost a major food source-frog.

So, every link in a food chain is vital for maintaining the balance of the entire community.
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?

If students notice fewer butterflies in their garden, several factors could be at play. Possible reasons include the use of chemical pesticides, Less growth of flowering plants where butterflies lay eggs, or local habitat destruction.

To bring the butterflies back, students can take these steps:

i.         They can grow more flowering plants that are rich in nectar.

ii.         Avoid using chemicals that kill beneficial insects.

iii.         Some host plants can also be grown for caterpillars.

iv.         Students can try to keep the garden clean and green to attract more butterflies.

6.Why is it not possible to have an ecosystem with only producers and no consumers or decomposers?

It is impossible to have an ecosystem with only producers. While plants can make their own food using sunlight, an ecosystem requires the movement of matter. Without consumers to control plant growth and decomposers to recycle waste, the system would become locked.

Producers like plants produce food with the help of sunlight, but they need consumers to use that energy and food. Consumers are needed for the energy transfer in the food chain. Decomposers like fungi and bacteria break down the dead plants and animals. These nutrients return to the soil, which then helps the plants to grow.

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?

If we observe a local park versus a roadside, we see distinct differences in their components:

• Park: High biodiversity. Living components include various trees, birds, squirrels, and insects. Non-living components include moist soil, benches, and clean air.
• Roadside: Low biodiversity. Living components might be limited to hardy weeds or occasional stray animals. Non-living components include asphalt, concrete, exhaust fumes, and litter.

The park is a more stable, complex ecosystem, while the roadside is a highly stressed environment dominated by human activity.

8. ‘Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable.’ Comment on the statement.

Agricultural fields are human-made ecosystems. They are necessary to feed billions of people, but they are often fragile because they lack biodiversity. To make them sustainable means using resources in a way that does not deplete them or harm the environment, we must practice crop rotation, use organic fertilizers, and conserve water. Otherwise the soil loses its fertility, and the ecosystem eventually fails to provide food.

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

If the Indian hare population drops due to disease, it directly impacts the food web. Predators that rely on the hare, such as foxes or wild cats, will face food shortages and may decline in number. Simultaneously, the plants that the hare usually eats might grow increasingly, changing the vegetation structure of the area.