Think It Over (Page No. 252)
1. How does the warming of Arabian Sea water affect the southwest monsoon in India?
Answer: Warmer Arabian Sea water leads to increased evaporation from the sea surface. This extra moisture in the atmosphere causes fluctuations in the southwest monsoon, resulting in variable rainfall — bringing floods to some regions of India while leaving others in drought. Essentially, a warmer sea disrupts the balance of the hydrosphere and intensifies the monsoon system unevenly.
2. If a large forest is cleared, how can that affect the flow of a river in that area?
Answer: Clearing a large forest reduces transpiration (water released by trees into the atmosphere), which can lower local rainfall over time. Without tree roots binding the soil, erosion increases and less water infiltrates into the ground, reducing groundwater recharge. This means less steady water feeds the river. Ironically, during rain events, more water runs off directly into the river (since it can’t be absorbed), potentially causing floods followed by dry spells — making river flow more erratic and unreliable.
3. What might happen to coastal cities in India if glaciers and polar ice keep melting faster?
Answer: Faster melting of glaciers and polar ice adds more water to rivers and oceans, raising sea levels over the long run. This threatens low-lying coastal cities like Mumbai and Chennai with flooding. Beyond direct inundation, habitat loss in coastal ecosystems (like mangroves) would follow, disrupting the biosphere and the livelihoods of millions who depend on coastal fisheries and agriculture.
4. How would increasing carbon dioxide levels in the atmosphere affect the ocean plankton?
Answer: Increasing atmospheric CO₂ causes the oceans to absorb more of it, making seawater more acidic. This ocean acidification threatens tiny plankton (including phytoplankton), which depend on carbonate ions to survive and photosynthesize. Since phytoplankton form the base of the marine food chain and produce a significant portion of Earth’s oxygen, their decline would cascade through the entire marine ecosystem. Additionally, warmer ocean temperatures (from global warming) reduce the ocean’s ability to absorb CO₂, compounding the problem further.
Pause and Ponder (Page No. 258)
1. Visit the website given below and study the effect of the concentration of greenhouse gas on surface temperature, https://phet.colorado. edu/en/simulations/ greenhouse-effect
Answer: By visiting the greenhouse effect simulation, we observe that as the concentration of greenhouse gases increases, the surface temperature of the Earth also increases. Greenhouse gases such as carbon dioxide, methane and water vapour trap more heat radiated from the Earth’s surface and prevent it from escaping into space. This increases the warming of the atmosphere and surface of the Earth.
When the concentration of greenhouse gases is low, more heat escapes into space and the Earth remains cooler. But when their concentration becomes high, more heat is trapped, leading to global warming and climate change.
Pause and Ponder (Page No. 261)
2. How does the cool mountain breeze benefit agriculture activity, particularly the crops and soil?
Answer: After sunset, mountain slopes cool down faster than the valley floor. The cool, dense air flows downward into the valley. This is called the mountain breeze.
Benefits to Agriculture:
1. Temperature Regulation:
- Cool nights help crops like tea, coffee, and apples (grown in Himalayan regions) to grow well.
- It reduces heat stress on plants during the night.
2. Moisture and Soil Health:
- Cool breeze reduces excessive evaporation, keeping soil moist for longer.
- It slows decomposition of organic matter, helping maintain soil fertility.
3. Pest and Disease Control:
- Cool temperatures create unfavourable conditions for harmful insects and fungal diseases, naturally protecting crops.
4. Quality of Produce:
- The contrast between warm days and cool nights improves the colour, sweetness, and overall quality of fruits like apples and pears.
Conclusion: Mountain breeze plays an important natural role in maintaining suitable conditions for healthy crop growth and fertile soil in hilly regions.
3. What happens to the warm surface of water from the equator as it travels toward the poles?
What impact does this movement have on the area?
Answer:
Journey of Warm Water:
- Near the equator, intense sunlight makes ocean water warm and less dense.
- Planetary winds push this warm surface water toward the poles.
- As it travels, it gradually loses heat to the atmosphere.
- Near the poles, it becomes cold, dense, and sinks to deeper ocean levels.
- Cold water then flows back toward the equator through deeper ocean layers, completing the circulation cycle.
Impacts of This Movement:
1. Climate Regulation:
- Warm currents like the North Atlantic Drift (extension of the Gulf Stream) keep northwestern Europe warmer than expected during winters.
2. Ice-Free Ports:
- Warm currents keep many ports ice-free in winter, supporting trade and shipping.
3. Rainfall:
- Warm water increases evaporation, adding moisture to the air and causing increased rainfall in nearby coastal areas.
4. Marine Ecosystems:
- Nutrients transported by these currents support rich marine life and fishing zones.
Conclusion: The movement of warm equatorial water toward the poles is a vital process that regulates climate, supports marine life, and connects the hydrosphere, atmosphere, and biosphere as parts of one Earth system.
Pause and Ponder (Page No. 263)
4. The CO₂ dissolved in the ocean is disturbed when the global temperature increases. What will happen to marine life?
Answer: When global temperature increases, the balance of CO₂ dissolved in ocean water gets disturbed. Warmer oceans absorb less carbon dioxide, and the increased CO₂ makes the water more acidic. This affects marine organisms such as plankton, corals and shell-forming animals. Coral reefs may get damaged, and many marine organisms may find it difficult to survive. As a result, marine food chains and ocean ecosystems may become disturbed.
Pause and Ponder (Page No. 265)
5. What would happen to plants and animals on Earth if the biogeochemical cycles were disrupted and stopped? Explain by giving a few examples.
Answer: If the biogeochemical cycles were disrupted or stopped, plants and animals would not get the essential nutrients needed for survival. The balance of nature would be disturbed, affecting all living organisms.
For example:
- If the carbon cycle stopped, plants would not get enough carbon dioxide for photosynthesis, so food production would decrease.
- If the oxygen cycle stopped, animals and humans would not get enough oxygen for respiration.
- If the nitrogen cycle stopped, plants would not receive nitrogen needed for making proteins and growth, leading to poor crop production.
- If the water cycle stopped, there would be no proper rainfall, causing droughts and shortage of water for living organisms.
Thus, disruption of biogeochemical cycles would seriously affect ecosystems and may threaten life on Earth.
Pause and Ponder (Page No. 266)
6. Discuss how human activities increase the concentration ofgreenhouse gases in the atmosphere.
What would you do as an individual to reduce the emission of greenhouse gas?
Answer: Human activities such as burning fossil fuels in vehicles, factories and power plants release large amounts of carbon dioxide into the atmosphere. Deforestation also increases greenhouse gases because fewer trees are available to absorb carbon dioxide during photosynthesis. The excessive use of fertilisers and industrial activities also release gases like methane and nitrous oxide, which contribute to global warming.
As an individual, I can help reduce greenhouse gas emissions by:
- Saving electricity and fuel
- Using public transport, cycling or walking whenever possible
- Planting more trees
- Reducing waste and recycling materials
- Conserving water and energy
- Using renewable sources of energy like solar energy whenever possible
These actions can help protect the environment and reduce global warming.
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