Exercises - Chapter 12: How Nature Works in Harmony

Questions and Answers

1. Refer to the given diagram (Population → Community → Ecosystem) 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: Statement (iii) is wrong. An ecosystem is not a part of a community; rather, a community (along with the abiotic environment and their interactions) is a part of an ecosystem. The correct hierarchy is: Individual $\rightarrow$ Population $\rightarrow$ Community $\rightarrow$ Ecosystem.

2. If all decomposers suddenly disappear from a forest ecosystem, what changes do you think would occur? Explain why decomposers are essential.

Answer: If decomposers (like bacteria and fungi) disappear:

Waste Accumulation: Dead plants, fallen leaves, and animal remains would pile up indefinitely as they would not be broken down.
Nutrient Depletion: Nutrients trapped in dead matter would not be returned to the soil.
Plant Death: Without recycled nutrients, the soil would lose its fertility, and plants would eventually stop growing and die.
Ecosystem Collapse: Since plants (producers) are the base of all food chains, their death would lead to the death of all consumers. Conclusion: Decomposers are essential because they recycle nutrients back into the environment, ensuring the continuity of life.

3. Selvam shared that his village was less affected by the 2004 Tsunami due to the presence of mangrove forests. How did mangroves protect the village?

Answer: Mangrove forests act as a natural buffer or shield. Their dense root systems and thick vegetation:

Slow down waves: They absorb the energy of strong tsunami waves and storm surges, reducing their height and speed before they reach human settlements.
Windbreaks: They slow down strong winds during storms.
Soil Stabilization: Their roots hold the soil firmly, preventing coastal erosion during floods.

4. Look at this food chain: Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake. If frogs disappear, what will happen to the population of grasshoppers and snakes? Why?

Answer:

Grasshoppers: Their population will increase rapidly because their natural predator (the frog) is gone. This may lead to over-grazing of grass.
Snakes: Their population will decrease because their primary source of food (the frog) is no longer available. Some snakes might die of starvation or be forced to find other prey.

5. In a school garden, students noticed fewer butterflies. What could be the reasons? What steps can they take?

Answer:

Possible Reasons: Use of synthetic pesticides in the garden, loss of host plants (where they lay eggs), or lack of flowering plants (nectar source).
Steps to take:
1. Plant a Pollinator Garden: Grow a variety of brightly coloured, nectar-rich flowering plants.
2. Avoid Pesticides: Stop using chemicals that harm beneficial insects.
3. Provide Host Plants: Identify and plant specific plants that local butterflies use for laying eggs (e.g., curry leaf plants, citrus).

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

Answer: An ecosystem needs balance and recycling.

Without consumers, the producer population would grow unchecked until they compete for space and resources, potentially leading to a crash.
Without decomposers, nutrients would stay locked in dead plants. Once the soil nutrients are exhausted, the producers would not be able to grow. Conclusion: All three roles are necessary to maintain a dynamic and sustainable cycle of energy and matter.

7. Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable. Comment.

Answer: Human-made ecosystems meet our needs for food and resources but often use monoculture (growing one crop) and synthetic chemicals (fertilisers/pesticides). These practices can lead to:

Soil Degradation: Loss of fertility and beneficial soil microbes.
Pollution: Chemicals leaching into groundwater.
Loss of Biodiversity: Habitats for birds and insects are destroyed. To be sustainable, these ecosystems should adopt organic farming, crop rotation, and natural pest control to protect the environment for future generations.

8. If the Indian hare population drops because of a disease, how would it affect the number of other organisms in a food web?

Answer:

Predators (Fox, Eagle): Their numbers would likely decrease due to the scarcity of prey (the hare).
Producers (Grass and Plants): Their numbers might increase initially because there are fewer hares to eat them.
Other Herbivores (e.g., Deer): They might face increased competition for space if plants grow excessively, or they might face increased predation pressure if predators like eagles and foxes switch their focus to them.

Exercises - Chapter 12: How Nature Works in Harmony

Questions and Answers

1. Refer to the given diagram (Population → Community → Ecosystem) 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.

2. If all decomposers suddenly disappear from a forest ecosystem, what changes do you think would occur? Explain why decomposers are essential.

Answer: If decomposers (like bacteria and fungi) disappear:

Waste Accumulation: Dead plants, fallen leaves, and animal remains would pile up indefinitely as they would not be broken down.
Nutrient Depletion: Nutrients trapped in dead matter would not be returned to the soil.
Plant Death: Without recycled nutrients, the soil would lose its fertility, and plants would eventually stop growing and die.
Ecosystem Collapse: Since plants (producers) are the base of all food chains, their death would lead to the death of all consumers. Conclusion: Decomposers are essential because they recycle nutrients back into the environment, ensuring the continuity of life.

3. Selvam shared that his village was less affected by the 2004 Tsunami due to the presence of mangrove forests. How did mangroves protect the village?

Answer: Mangrove forests act as a natural buffer or shield. Their dense root systems and thick vegetation:

Slow down waves: They absorb the energy of strong tsunami waves and storm surges, reducing their height and speed before they reach human settlements.
Windbreaks: They slow down strong winds during storms.
Soil Stabilization: Their roots hold the soil firmly, preventing coastal erosion during floods.

4. Look at this food chain: Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake. If frogs disappear, what will happen to the population of grasshoppers and snakes? Why?

Answer:

Grasshoppers: Their population will increase rapidly because their natural predator (the frog) is gone. This may lead to over-grazing of grass.
Snakes: Their population will decrease because their primary source of food (the frog) is no longer available. Some snakes might die of starvation or be forced to find other prey.

5. In a school garden, students noticed fewer butterflies. What could be the reasons? What steps can they take?

Answer:

Possible Reasons: Use of synthetic pesticides in the garden, loss of host plants (where they lay eggs), or lack of flowering plants (nectar source).
Steps to take:
1. Plant a Pollinator Garden: Grow a variety of brightly coloured, nectar-rich flowering plants.
2. Avoid Pesticides: Stop using chemicals that harm beneficial insects.
3. Provide Host Plants: Identify and plant specific plants that local butterflies use for laying eggs (e.g., curry leaf plants, citrus).

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

Answer: An ecosystem needs balance and recycling.

Without consumers, the producer population would grow unchecked until they compete for space and resources, potentially leading to a crash.
Without decomposers, nutrients would stay locked in dead plants. Once the soil nutrients are exhausted, the producers would not be able to grow. Conclusion: All three roles are necessary to maintain a dynamic and sustainable cycle of energy and matter.

7. Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable. Comment.

Soil Degradation: Loss of fertility and beneficial soil microbes.
Pollution: Chemicals leaching into groundwater.
Loss of Biodiversity: Habitats for birds and insects are destroyed. To be sustainable, these ecosystems should adopt organic farming, crop rotation, and natural pest control to protect the environment for future generations.

8. If the Indian hare population drops because of a disease, how would it affect the number of other organisms in a food web?

Answer:

Predators (Fox, Eagle): Their numbers would likely decrease due to the scarcity of prey (the hare).
Producers (Grass and Plants): Their numbers might increase initially because there are fewer hares to eat them.
Other Herbivores (e.g., Deer): They might face increased competition for space if plants grow excessively, or they might face increased predation pressure if predators like eagles and foxes switch their focus to them.

Chapter 12: How Nature Works in Harmony - Exercises

Exercises - Chapter 12: How Nature Works in Harmony

Questions and Answers

1. Refer to the given diagram (Population → Community → Ecosystem) and select the wrong statement.

2. If all decomposers suddenly disappear from a forest ecosystem, what changes do you think would occur? Explain why decomposers are essential.

3. Selvam shared that his village was less affected by the 2004 Tsunami due to the presence of mangrove forests. How did mangroves protect the village?

4. Look at this food chain: Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake. If frogs disappear, what will happen to the population of grasshoppers and snakes? Why?

5. In a school garden, students noticed fewer butterflies. What could be the reasons? What steps can they take?

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

7. Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable. Comment.

8. If the Indian hare population drops because of a disease, how would it affect the number of other organisms in a food web?

On this page

Chapter 12: How Nature Works in Harmony - Exercises

Exercises - Chapter 12: How Nature Works in Harmony

Questions and Answers

1. Refer to the given diagram (Population → Community → Ecosystem) and select the wrong statement.

2. If all decomposers suddenly disappear from a forest ecosystem, what changes do you think would occur? Explain why decomposers are essential.

3. Selvam shared that his village was less affected by the 2004 Tsunami due to the presence of mangrove forests. How did mangroves protect the village?

4. Look at this food chain: Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake. If frogs disappear, what will happen to the population of grasshoppers and snakes? Why?

5. In a school garden, students noticed fewer butterflies. What could be the reasons? What steps can they take?

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

7. Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable. Comment.

8. If the Indian hare population drops because of a disease, how would it affect the number of other organisms in a food web?

On this page