NCERT Solutions for Class 9 Science Exploration Chapter 13

Earth system refers to the connected working of the geosphere, hydrosphere, cryosphere, atmosphere, and biosphere through the flow of energy and cycling of matter.
Solar radiation, winds, ocean currents, biogeochemical cycles, and human activities influence how matter and energy move across these spheres.

NCERT Solutions for Class 9 Science Exploration Chapter 13 help students solve Earth as a System: Energy, Matter, and Life from the Class 9 Science textbook. This chapter explains Earth’s spheres, uneven heating, solar radiation, albedo, atmosphere, greenhouse effect, winds, ocean currents, water cycle, carbon cycle, nitrogen cycle, oxygen cycle, and human impact on Earth processes. These NCERT Class 9 Science Solutions cover Pause and Ponder questions and all Class 9 Science Chapter 13 exercise solutions in a direct, exam-ready format.

Key Takeaways

• Earth system: Earth works through interactions among land, water, ice, air, and living organisms.
• Solar radiation: The Sun is the main energy source that drives winds, water cycle, ocean currents, and climate.
• Biogeochemical cycles: Water, carbon, nitrogen, and oxygen move between living and non-living parts of Earth.
• Human impact: Deforestation, fossil fuel use, pollution, and excess fertilisers disturb Earth’s natural cycles.

NCERT Solutions for Class 9 Science Exploration Chapter 13 Structure 2026

NCERT Solutions for Class 9 Science Exploration Chapter 13 In-Text Questions

Class 9 Science Exploration Chapter 13 uses Earth’s spheres, solar radiation, local winds, ocean currents, biogeochemical cycles, and climate change examples to explain Earth as one connected system.

Q1. How does greenhouse gas concentration affect surface temperature?

Answer: Increasing greenhouse gas concentration increases Earth’s surface temperature.

Explanation:
Greenhouse gases such as carbon dioxide, methane, and water vapour absorb outgoing infrared radiation from Earth’s surface. This traps heat in the atmosphere and keeps Earth warm enough for life.

However, when greenhouse gas concentration becomes too high, more heat is trapped. This enhances the greenhouse effect and causes global warming.

So, a rise in greenhouse gases leads to a rise in surface temperature.

Q2. How does cool mountain breeze benefit agriculture, particularly crops and soil?

Answer: Cool mountain breeze can help agriculture by lowering temperature, reducing heat stress in crops, and helping maintain soil moisture.

Explanation:
At night, mountain slopes cool faster. The cool, dense air moves down into the valley as mountain breeze.

This cooler air can reduce excessive heat around crops. It may also slow down evaporation from soil, helping retain moisture.

In hilly areas, such local winds influence temperature, humidity, crop growth, and soil conditions.

Q3. What happens to warm surface water from the equator as it travels towards the poles?

Answer: Warm surface water from the equator carries heat towards the poles and gradually cools.

Explanation:
Ocean currents transport warm water from equatorial regions to cooler regions. As the water moves towards the poles, it loses heat to the surroundings.

This movement reduces temperature differences between the equator and poles. It also moderates climate in nearby coastal regions.

For example, warm ocean currents help keep some high-latitude coastal regions warmer than expected.

Q4. What happens to marine life when dissolved CO₂ in ocean water is disturbed by global warming?

Answer: Marine life can be harmed because excess dissolved carbon dioxide can make seawater more acidic and disturb ocean ecosystems.

Explanation:
Oceans absorb carbon dioxide from the atmosphere. When atmospheric CO₂ increases, more CO₂ may dissolve in seawater.

This can change ocean chemistry and affect organisms like plankton, corals, and shell-forming animals. If plankton are affected, food chains in the ocean may also be disturbed.

Warmer ocean water can also reduce the ocean’s ability to absorb CO₂, worsening the imbalance.

Q5. What would happen if biogeochemical cycles were disrupted and stopped?

Answer: Life on Earth would be severely affected because essential nutrients and materials would stop being recycled.

Explanation:
Biogeochemical cycles keep water, carbon, nitrogen, and oxygen moving between air, water, soil, rocks, and living organisms.

If the water cycle stopped, rainfall, rivers, groundwater recharge, and agriculture would be affected.

If the carbon cycle stopped, photosynthesis, respiration, and climate balance would be disturbed.

If the nitrogen cycle stopped, plants would not get usable nitrogen for making proteins and nucleic acids.

If the oxygen cycle stopped, oxygen used in respiration and combustion would not be restored properly.

Q6. How do human activities increase greenhouse gases? What can individuals do to reduce emissions?

Answer: Human activities increase greenhouse gases through burning fossil fuels, deforestation, transport, industries, and wasteful energy use.

Explanation:
Burning coal, petrol, diesel, and natural gas releases carbon dioxide. Deforestation reduces the number of trees that absorb carbon dioxide through photosynthesis. Agriculture, waste, and livestock can add methane and other gases.

Individuals can reduce greenhouse gas emissions by:

1. Saving electricity
2. Using public transport, cycling, or walking when possible
3. Reducing waste
4. Reusing and recycling materials
5. Planting and protecting trees
6. Conserving water and food
7. Supporting solar and other renewable energy sources

These actions help reduce pressure on Earth’s systems.

NCERT Solutions for Class 9 Science Exploration Chapter 13 Exercise Questions

The Revise, Reflect, Refine section includes MCQs, reasoning-based questions, diagrams, and applications from Earth’s energy flow, atmospheric layers, climate change, and biogeochemical cycles.

Q1. Choose the role of biogeochemical cycles in an ecosystem.

Answer: The correct option is (ii) To recycle essential nutrients between biotic and abiotic components.

Explanation:
Biogeochemical cycles move essential substances such as water, carbon, nitrogen, and oxygen between living organisms and non-living components like air, water, soil, and rocks.

They do not create new elements. They recycle existing matter and make nutrients available again.

Q2. Which option explains what primarily warms Earth?

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

Explanation:
Solar radiation reaches Earth’s surface and warms it. The warmed surface gives out heat in the form of infrared radiation.

Greenhouse gases absorb part of this outgoing infrared radiation and trap heat in the atmosphere.

This process helps maintain a suitable temperature for life.

Q3. Explain how climate change affects the water cycle with examples.

Answer: Climate change affects the water cycle by changing evaporation, rainfall, snowfall, glacier melting, groundwater recharge, and drought patterns.

Explanation:
A warmer atmosphere can hold more water vapour. This may lead to intense rainfall in some regions and drought in others.

Examples:

1. Warmer temperatures increase evaporation from oceans and lakes.
2. Heavy rainfall can cause floods and soil erosion.
3. Less snowfall reduces water stored in the cryosphere.
4. Melting glaciers initially increase river water but can reduce long-term water availability.
5. Sudden rainfall causes more runoff and less groundwater recharge.
6. Coastal cities may face risk due to sea-level rise caused by melting ice and warming oceans.

Thus, climate change disturbs the balance between atmosphere, hydrosphere, cryosphere, geosphere, and biosphere.

Q4. Describe how albedo affects Earth’s surface temperature and climate.

Answer: Albedo affects temperature by controlling how much solar radiation a surface reflects.

Explanation:
Albedo is the fraction of solar radiation reflected by a surface.

High-albedo surfaces reflect more sunlight and remain cooler. Snow and ice have high albedo.

Low-albedo surfaces absorb more sunlight and become warmer. Ocean water, black soil, and dark roads have low albedo.

If ice melts, high-albedo ice is replaced by darker ocean or land surfaces. These absorb more heat and can increase warming.

This affects climate by changing how much heat Earth’s surface stores.

Q5. How are mountain and valley breezes formed? Would breezes differ over grassy and rocky mountains?

Answer: Mountain and valley breezes form because slopes and valley floors heat and cool at different rates.

Explanation:
During the day, mountain slopes heat faster than the valley floor. Warm air over the slopes rises, and cooler air from the valley moves upward. This is called a valley breeze.

At night, mountain slopes cool faster. Cool, dense air flows down the slopes into the valley. This is called a mountain breeze.

If one mountain is grassy and another is covered with barren rocks, their breezes may differ. Barren rocks heat up and cool down faster, so the air above them may show stronger temperature changes. Grass-covered slopes remain cooler due to shade and transpiration.

So, the breeze from a rocky mountain may be warmer during the day and cooler at night compared to a grassy mountain.

Q6. Which atmospheric layer is responsible for winds, storms, and rainfall? Why?

Answer: The troposphere is mainly responsible for winds, storms, rainfall, and other weather phenomena.

Explanation:
The troposphere is the lowest layer of the atmosphere. It is heated from Earth’s surface.

Warm air rises, cools, and causes changes in pressure, cloud formation, winds, rainfall, and storms.

Temperature generally decreases with height in the troposphere. This supports vertical mixing of air, which drives weather.

Q7. Explain the nitrogen cycle. How would life be affected if nitrogen were not cycled?

Answer: The nitrogen cycle converts atmospheric nitrogen into usable forms and returns it to the atmosphere.

Explanation:
Nitrogen is needed to make proteins and nucleic acids. However, plants and animals cannot directly use atmospheric nitrogen gas.

Main steps:

1. Nitrogen fixation: Bacteria such as Rhizobium and Azotobacter convert atmospheric nitrogen into ammonia.
2. Nitrification: Bacteria convert ammonia into nitrites and then nitrates.
3. Assimilation: Plants absorb nitrates and make proteins and other nitrogen compounds.
4. Feeding: Animals get nitrogen by eating plants or other animals.
5. Ammonification: Decomposers break down dead matter and waste, releasing ammonia into soil.
6. Denitrification: Bacteria convert nitrates back into nitrogen gas.

If nitrogen were not cycled, plants would not get usable nitrogen. Plant growth would reduce, food chains would collapse, and life would be severely affected.

Q8. What are the impacts of deforestation on oxygen and carbon cycles? What are other consequences?

Answer: Deforestation reduces oxygen production and increases carbon dioxide levels.

Explanation:
Trees absorb carbon dioxide during photosynthesis and release oxygen. When forests are cleared, less CO₂ is absorbed and less oxygen is produced.

If trees are burnt or decay after cutting, stored carbon is released back as CO₂. This increases greenhouse gas concentration.

Other consequences of deforestation:

1. Soil erosion increases.
2. Local rainfall may decrease because transpiration reduces.
3. Biodiversity declines due to habitat loss.
4. Flood risk may increase.
5. Groundwater recharge may reduce.
6. Local climate becomes warmer and drier.
7. Food webs and ecosystems are disturbed.

Q9. Explain the path carbon takes to return to the atmosphere. Start from plants using CO₂.

Answer: Carbon enters plants through photosynthesis and returns to the atmosphere through respiration, decomposition, and combustion.

Explanation:
Path of carbon:

$CO_2 , in , atmosphere \rightarrow Plants , through , photosynthesis \rightarrow Animals , through , food \rightarrow Respiration \rightarrow CO_2 , back , to , atmosphere$

Another path:

$Plants , and , animals \rightarrow Dead , organic , matter \rightarrow Decomposition \rightarrow CO_2 , back , to , atmosphere$

A long-term path:

$Dead , organisms \rightarrow Fossil , fuels \rightarrow Burning , of , fuels \rightarrow CO_2 , back , to , atmosphere$

So, carbon moves between atmosphere, biosphere, geosphere, and hydrosphere through the carbon cycle.

Q10. Why is excess CO₂ undesirable even though plants need it?

Answer: Excess CO₂ is undesirable because it intensifies the greenhouse effect and causes global warming.

Explanation:
Plants need carbon dioxide for photosynthesis. A small amount of CO₂ in the atmosphere helps maintain Earth’s temperature.

However, too much CO₂ traps extra heat. This can cause:

1. Rise in global temperature
2. Melting of glaciers and polar ice
3. Sea-level rise
4. More extreme weather
5. Changes in rainfall patterns
6. Harm to marine ecosystems due to ocean acidification
7. Stress on crops and biodiversity

So, CO₂ is useful in balance but harmful in excess.

Q11. How is heat lost from Earth’s surface? What is its significance?

Answer: Heat is lost from Earth’s surface mainly through re-radiation as infrared radiation.

Explanation:
Earth absorbs solar radiation and becomes warm. It then emits heat back in the form of infrared radiation.

Some of this outgoing heat escapes to space. Some is absorbed by greenhouse gases and re-radiated back, keeping Earth warm.

This process is significant because it maintains Earth’s energy balance. Without heat loss, Earth would become too hot. Without greenhouse gases, Earth would be too cold for life.

Q12. If Earth were a flat disc instead of a sphere, how would solar radiation and temperature patterns change?

Answer: If Earth were a flat disc, solar radiation would be distributed differently, and the present latitude-based temperature zones would not form in the same way.

Explanation:
Earth’s spherical shape causes sunlight to fall more directly near the equator and more slantingly near the poles. This creates uneven heating and temperature differences.

If Earth were flat, sunlight would fall more evenly over large areas, depending on the Sun’s position. The strong equator-to-pole temperature pattern would be absent or very different.

This would affect wind belts, ocean currents, climate zones, seasons, and ecosystems.

Q13. How would rising atmospheric temperature affect the cryosphere, hydrosphere, and biosphere?

Answer: Rising atmospheric temperature would melt ice, change water availability, and disturb living organisms and habitats.

Explanation:

For example, melting Himalayan glaciers may affect river flow. Sea-level rise may threaten coastal regions. Warmer oceans may harm plankton and coral reefs.

Q14. How does Earth’s atmosphere maintain a suitable temperature for life?

Answer: Earth’s atmosphere maintains temperature by filtering harmful radiation and trapping some outgoing heat.

Explanation:
The ozone layer absorbs harmful ultraviolet radiation from the Sun. Clouds, gases, and dust also absorb or reflect part of incoming sunlight.

Earth’s surface absorbs solar radiation and re-radiates heat as infrared radiation. Greenhouse gases such as carbon dioxide, methane, and water vapour trap some of this heat.

This natural greenhouse effect keeps Earth warm enough for life. Without it, Earth would be too cold.

However, excess greenhouse gases can cause overheating and global warming.

Q15. Describe the interrelationship between different spheres of Earth with an example.

Answer: Earth’s spheres are interconnected because energy and matter move continuously between them.

Explanation:
The main spheres are:

1. Geosphere: Rocks, soil, landforms, and Earth’s interior
2. Hydrosphere: Rivers, lakes, oceans, groundwater
3. Cryosphere: Ice, snow, glaciers
4. Atmosphere: Air around Earth
5. Biosphere: Living organisms and habitats

Example:

Less snowfall affects the cryosphere. When snow melts less in summer, lakes and rivers receive less water, affecting the hydrosphere.

Less water reduces grass growth, affecting the biosphere. Dry soil can increase erosion, affecting the geosphere. Reduced water and vegetation may also affect local humidity and air temperature, affecting the atmosphere.

This shows that a disturbance in one sphere can change all others.

NCERT Solutions for Class 9 Science Exploration

Topics Covered in NCERT Solutions for Class 9 Science Exploration Chapter 13

Class 9 Science Exploration Chapter 13 covers Earth as an interconnected system. It explains how energy and matter move through Earth’s spheres and how human actions disturb natural processes.

• Earth as a System Energy Matter and Life Class 9
• Earth spheres Class 9 Science
• Geosphere, hydrosphere, cryosphere, atmosphere, and biosphere
• Uneven heating of Earth Class 9
• Solar radiation Class 9
• Electromagnetic spectrum
• Insolation and solar constant
• Albedo Class 9 Science
• Urban heat island effect
• Latitude and Earth’s shape
• Role of atmosphere
• Troposphere and stratosphere
• Greenhouse effect Class 9
• Local winds, valley breeze, and mountain breeze
• Planetary winds
• Winds and ocean currents Class 9
• Biogeochemical cycles Class 9
• Water cycle carbon cycle nitrogen cycle oxygen cycle Class 9
• Human impact on Earth processes Class 9
• Deforestation, fossil fuels, eutrophication, and air pollution
• Sustainable practices and resource conservation

Important Concepts in NCERT Solutions for Class 9 Science Exploration Chapter 13

Class 9 Science Chapter 13 solutions require students to understand Earth as one connected system where changes in one sphere affect other spheres.

Important Formulas in NCERT Solutions for Class 9 Science Exploration Chapter 13

Class 9 Science Chapter 13 includes a few calculation-based ideas related to solar energy and radiation.