Earth as a System Energy Matter and Life Class 9 NCERT Solutions

← Back to Class 9 Science NCERT Solutions

Earth as a System: Energy, Matter and Life Class 9 NCERT Solutions provide simple, accurate, and step-by-step answers to all the textbook questions based on the latest NCERT Class 9 Science syllabus. These solutions explain how energy flows through ecosystems, how matter is recycled by biogeochemical cycles, and how living and non-living components interact to maintain life on Earth.

Earth as a System Energy Matter and Life Class 9 NCERT Solutions

Q1. How does the warming of Arabian Sea water affect the southwest monsoon in India?

Answer: Warming of the Arabian Sea water increases evaporation. This adds more moisture to the air and changes the southwest monsoon.

• Some areas get heavy rain and floods.
• Other areas face less rain and drought.
• Monsoon becomes uneven and uncertain.

Q2. If a large forest is cleared, how can that affect the flow of a river in that area?

Answer: If a large forest is cleared, the flow of a river in that area changes.

• Trees normally hold soil and water. Without them, rainwater runs off quickly.
• This causes soil erosion and makes rivers muddy.
• Less water seeps into the ground, so groundwater reduces.
• Rivers may have floods in rainy season and less water in dry season.

Q3. What might happen to coastal cities in India if glaciers and polar ice keep melting faster?

Answer: If glaciers and polar ice keep melting faster, coastal cities in India will face serious problems.

• Sea level will rise, because melted ice adds more water to the oceans.
• Low‑lying cities like Mumbai, Chennai, and Kolkata may face flooding.
• Habitats and homes near the coast can be lost.
• Saltwater may enter rivers and groundwater, making drinking water and farming difficult.

Q4. How would increasing carbon dioxide levels in the atmosphere affect the ocean plankton?

Answer: Increasing carbon dioxide (CO₂) levels in the atmosphere affect the ocean plankton in two main ways:

• Extra CO₂ dissolves in ocean water, making it more acidic. Acidic water harms plankton, especially those with shells made of calcium.
• Plankton are the base of the marine food chain. If their numbers drop, fish and other sea life also suffer.

Q5. How does the cool mountain breeze benefit agriculture activity, particularly the crops and soil?

Answer: The cool mountain breeze helps agriculture in simple but important ways:

• At night, cool air flows down the slopes into the valley. This lowers the temperature and prevents crops from overheating.
• It keeps the soil moist by reducing evaporation of water.
• The breeze also refreshes the plants, helping them grow better.
• Overall, it protects crops and soil, making farming in mountain valleys more healthy and productive.

Q6. 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: The warm surface water from the equator moves toward the poles with the help of ocean currents.

• As it travels, it carries heat from the equator to colder regions.
• This makes the polar areas less cold and helps balance temperatures across the Earth.
• It also keeps some places, like northwestern Europe, warmer in winter and even keeps ports ice‑free.
• Along the way, these currents also transport nutrients, supporting marine life.

Q7. 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 CO₂ dissolved in the ocean gets disturbed.

• Warmer water holds less CO₂, so more of it escapes back into the air, worsening global warming.
• The ocean also becomes more acidic. Acidic water harms plankton, corals, and shell‑making animals.
• If plankton decline, the whole marine food chain suffers, because fish and other sea life depend on them.

Q8. 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 (like water, carbon, nitrogen, oxygen cycles) were disrupted or stopped, plants and animals would not survive properly.

• Plants: They need carbon dioxide for photosynthesis and nitrogen for proteins. If these cycles stop, plants cannot make food or grow. Example: crops would fail without the nitrogen cycle.
• Animals: They depend on plants for food and oxygen. If plants die, animals lose food and oxygen. Example: fish would die if the oxygen cycle in water is disturbed.
• Humans: We depend on both plants and animals. If cycles stop, farming, forests, and fisheries collapse, leading to food shortage.

Q9. Discuss how human activities increase the concentration of greenhouse gases in the atmosphere. What would you do as an individual to reduce the emission of greenhouse gas?

Answer: Human activities increase greenhouse gases like CO₂, CH₄, and others in the atmosphere mainly through:

• Burning fossil fuels (coal, oil, gas) for electricity, transport, and industry.
• Deforestation, which reduces trees that absorb CO₂.
• Agriculture, especially rice fields and cattle, which release methane.
• Industrial processes and waste burning that add gases to the air.

These gases trap heat and cause global warming.

As an individual, you can reduce emissions by:

• Using public transport, cycling, or walking instead of private vehicles.
• Saving electricity (switching off lights, using energy‑efficient appliances).
• Planting trees and protecting green areas.
• Reducing plastic use and recycling waste.
• Supporting solar and renewable energy at home or in community projects.

Q10. Choose the most appropriate option to describe the role of biogeochemical cycles in an ecosystem.
(i) To provide food directly to all organisms.
(ii) To recycle essential nutrients between biotic and abiotic components.
(iii) To create new elements for use by living things.
(iv) To remove pollutants and toxins from the organism.

Answer: (iii) To create new elements for use by living things.

Explanation:

Biogeochemical cycles keep the balance of life by recycling nutrients like carbon, nitrogen, oxygen, and water between living things (plants, animals) and non‑living parts (air, soil, water). Without these cycles, plants and animals would not get the materials they need to survive.

Q11. Which of the following is primarily responsible for warming of the Earth?
(i) Solar radiation is immediately absorbed by carbon dioxide, which then releases it as heat.
(ii) The atmosphere’s tiny particles absorb incoming solar radiation, which directly heats the Earth.
(iii) The Earth’s surface absorbs solar radiation, which is then re-radiated and trapped by greenhouse gases.
(iv) The Earth’s environment is heated only by the solar radiation reflected by the clouds.

Answer: (iii) The Earth’s surface absorbs solar radiation, which is then re-radiated and trapped by greenhouse gases.

Explanation:

• The Earth’s surface takes in sunlight and warms up.
• It then re‑radiates heat as infrared radiation.
• Greenhouse gases like CO₂, CH₄, and water vapour trap part of this heat.
• This process keeps the Earth warm enough for life, but too much trapping causes global warming.

Q12. Explain how climate change affects the water cycle. Illustrate with examples.

Answer: Climate change affects the water cycle by disturbing how water moves between air, land, and oceans.

• A warmer atmosphere holds more moisture. This causes heavier rains in some places (like stronger monsoons in India).
• At the same time, other areas face long droughts, because rainfall becomes uneven.
• Melting glaciers add more water to rivers, which can cause floods and raise sea levels, threatening coastal cities like Mumbai and Chennai.
• Sudden heavy rains increase runoff, leading to soil erosion and less groundwater recharge, making farming harder in dry months.

Example: In India, climate change makes monsoons more intense in some regions while reducing rainfall in others, directly affecting crops, rivers, and people’s lives.

Q13. Describe how albedo affects the Earth’s surface temperature and its climate.

Answer: Albedo means how much sunlight a surface reflects. It directly affects Earth’s temperature and climate.

• High albedo surfaces (like snow and ice) reflect most sunlight. They stay cool and keep the surrounding climate colder. Example: polar regions remain very cold because ice reflects 80–90% of sunlight.
• Low albedo surfaces (like black soil, oceans, or asphalt roads) absorb more sunlight. They heat up quickly and make the area warmer. Example: cities with concrete and asphalt become hotter, causing the urban heat island effect.

Q14. How are mountain and valley breezes formed? Suppose there are two mountains, one covered with grass and another covered with barren rocks; would the temperature of the two mountain breezes be different? If so, how?

Answer: Mountain and valley breezes are formed because slopes and valleys heat and cool at different rates.

• Daytime (Valley breeze): Mountain slopes heat faster than the valley floor. Warm air rises from the slopes, and cooler air from the valley moves upward to replace it.
• Nighttime (Mountain breeze): Slopes cool faster after sunset. Cold, dense air flows down into the valley, creating a mountain breeze.

If one mountain is covered with grass and the other with barren rocks, their breezes will be different:

Grass absorbs less heat and stays cooler, so its breeze will be milder and cooler.
Barren rocks absorb more heat during the day and lose it quickly at night, so their breeze will be stronger and colder.

Q15. You have witnessed weather phenomena, such as winds, storms, rainfall, etc. Which atmospheric layer is mainly responsible for such phenomena and what is the primary reason for its occurrence?

Answer: All the weather phenomena you see — winds, storms, rainfall — mainly occur in the troposphere, which is the lowest layer of the atmosphere.

• The troposphere extends up to about 8–18 km above Earth’s surface.
• It contains almost all the water vapour, dust, and clouds.

The primary reason for these phenomena is the uneven heating of Earth’s surface by the Sun. Warm air rises, cool air sinks, and this movement creates winds, clouds, and rainfall.

Q16. Explain the processes involved in the nitrogen cycle. How would life on Earth be affected if nitrogen were not cycled?

Answer: The nitrogen cycle keeps nitrogen moving between air, soil, and living things.

• Fixation: Bacteria change nitrogen gas into usable forms.
• Nitrification & Assimilation: Plants absorb nitrates, animals get nitrogen by eating plants.
• Ammonification & Denitrification: Decomposers return nitrogen to soil, and some bacteria release it back to the air.

Q17. What are the impacts of deforestation on the Earth’s oxygen and carbon cycles? What are the other consequences of deforestation?

Answer: Deforestation has serious impacts on both the oxygen cycle and the carbon cycle:

Impact on Oxygen Cycle

• Trees release oxygen during photosynthesis.
• Cutting forests reduces oxygen production, making the air less fresh and healthy.

Impact on Carbon Cycle

• Trees absorb carbon dioxide (CO₂) and store carbon in their biomass.
• When forests are cut or burned, this stored carbon is released back into the atmosphere.
• This increases greenhouse gases, leading to global warming.

Other Consequences of Deforestation

• Loss of biodiversity: Animals and plants lose their natural habitat.
• Soil erosion: Without roots to hold soil, it washes away during rains.
• Disturbed rainfall patterns: Forests help maintain the water cycle; their loss can cause droughts or floods.
• Climate change acceleration: Less carbon absorption and more CO₂ release worsen climate imbalance.

Q18. Explain with suitable diagram the path that carbon takes to go back to the atmosphere. You may start from plants using CO₂ from the atmosphere.

Answer:

Steps in the Carbon Cycle

• Photosynthesis: Plants take in CO₂ from the atmosphere and use it to make food.
• Respiration: Plants and animals release CO₂ back into the air when they breathe.
• Decomposition: When plants and animals die, decomposers break them down, releasing CO₂.
• Combustion: Burning of wood or fossil fuels releases stored carbon as CO₂.
• Ocean release: Oceans absorb CO₂, but also release it back into the atmosphere.

Q19. Why is an excess of CO₂ in the atmosphere considered undesirable even though it is required by plants?

Answer: An excess of CO₂ in the atmosphere is undesirable even though plants need it for photosynthesis.

• Plants use only a small amount of CO₂. Too much traps heat and causes the greenhouse effect, leading to global warming.
• Rising temperatures disturb the climate, melt glaciers, and cause floods and droughts.
• It also makes oceans more acidic, harming marine life.

Q20. How is heat lost from the surface of the Earth? What is its significance?

Answer: Heat is lost from the Earth’s surface mainly through radiation.

The Earth absorbs sunlight during the day and then re‑radiates heat as infrared rays at night.
Some of this heat escapes into space, while part is trapped by greenhouse gases, keeping the planet warm.

Significance

• This process maintains the temperature balance of Earth.
• Without heat loss, the planet would become too hot; if too much escaped, it would become too cold.

Q21. If the Earth were a flat disc instead of a sphere, how would the patterns of solar radiation and temperature be different?

Answer: If the Earth were a flat disc instead of a sphere, the way solar radiation and temperature patterns work would be very different:

Solar Radiation Patterns

• On a sphere, sunlight spreads unevenly: direct at the equator, slanted at the poles.
• On a flat disc, sunlight would fall more evenly across the surface, with little variation in angle.
• This means there would be less difference between hot and cold regions.

Temperature Differences

• A sphere creates climate zones (tropics, temperate, polar) because of curvature.
• A flat disc would have uniform heating, so no clear zones.
• Winds, ocean currents, and seasons would be very different or might not exist at all.

Q22. Suppose there is a rise in atmospheric temperature on Earth. How would this affect the cryosphere, hydrosphere and biosphere?

Answer: A rise in atmospheric temperature affects Earth’s systems like this:

• Cryosphere: Glaciers and ice melt, reducing albedo and raising sea levels.
• Hydrosphere: More evaporation → heavy rains, storms, droughts, and warmer oceans.
• Biosphere: Plants, animals, and humans face habitat loss, crop failures, and health risks.

Q23. Explain how the Earth’s atmosphere helps in maintaining a suitable temperature for life to survive on the Earth.

Answer: The Earth’s atmosphere keeps life possible by acting like a blanket:

• It traps some heat through the greenhouse effect so Earth doesn’t get too cold.
• It lets excess heat escape so Earth doesn’t get too hot.
• It spreads heat with winds and weather systems, balancing day–night and equator–pole temperatures.

Q24. Describe the interrelationship between different spheres of the Earth. Illustrate with example how these spheres function in a delicate balance.

Answer: The Earth’s spheres work together in balance:

• Atmosphere: Provides air and regulates temperature.
• Hydrosphere: Water supports life and shapes climate.
• Lithosphere: Landforms influence ecosystems and weather.
• Biosphere: Living things depend on air, water, and land.
• Cryosphere: Ice controls temperature and sea levels.

Example: Deforestation (biosphere) reduces CO₂ absorption, warming the atmosphere, melting ice in the cryosphere, raising sea levels in the hydrosphere, and eroding soil in the lithosphere.

Disclaimer: The content that is present on our website is based on the NCERT Class 9 Science textbook and is provided for educational purposes only. All the content and images have been taken from Science Class 9 NCERT Textbook and CBSE Support material. Images and content shown above are the property of individual organizations and are used here for reference purposes only. To make it easy to understand, some of the content and images are generated by AI and cross-checked by the teachers.

← Back to Class 9 Science NCERT Solutions