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NCERT Solutions for Class 9 Science Chapter 13 Earth as a System: Energy, Matter and Life
NCERT Solutions for Class 9 Science Chapter 13 are prepared according to the latest NCERT syllabus (2026–27) and CBSE curriculum to help students learn every concept with confidence. Designed by ALLEN Experts, these solutions provide accurate and step-wise answers to all NCERT exercise questions which makes it easier to understand the concepts, complete assignments and prepare well for school and CBSE examinations.
Students can also download the free PDF and study offline and revise quickly at any time. The resource also provides vital questions, chapter-wise practice, comprehensive solutions and exam-centric explanations for steady learning and better academic results.
1.0 Download NCERT Class 9 Science Chapter 13 Earth as a System: Energy,Matter and Life
Earth as a System: Energy, Matter and Life explains the movement of energy and the cycling of matter through Earth’s interconnected systems to sustain life and maintain ecological balance.
Download NCERT Solutions for Class 9 Science Chapter 13 free PDF. NCERT Solutions are solved by ALLEN Experts as per the latest NCERT syllabus and CBSE curriculum, step by step to help students learn and revise the concepts easily.
2.0 Learning Outcomes – NCERT Class 9 Science Chapter 13: Earth as a System: Energy, Matter and Life
- Discover how the biosphere, geosphere, hydrosphere, cryosphere and atmosphere work together as interdependent Earth systems.
- Describe the role of solar energy in the natural processes of Earth and how it is the basis of life.
- Understand the causes of winds and other atmospheric phenomena, caused by the differential heating of Earth’s surface
- Describe the water, carbon, nitrogen, and oxygen cycles and explain how they recycle matter.
- Explain the significance of the biotic and abiotic components in maintaining ecological balance.
- Examine the impact of human actions on Earth’s systems and the importance of sustainable practices.
3.0Detailed Class 9 Science Chapter 13: Earth as a System: Energy, Matter and Life Solutions
1. 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.
Solution
(ii) To recycle essential nutrients between biotic and abiotic components. Biogeochemical cycles continuously circulate nutrients such as carbon, nitrogen, oxygen, and water between living organisms (biotic components) and the environment (abiotic components). This recycling ensures the availability of essential nutrients required for life.
2. 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.
Solution
(iii) The Earth's surface absorbs solar radiation, which is then re-radiated and trapped by greenhouse gases.
The Sun's energy reaches the Earth and warms its surface. The Earth then emits this energy as infrared radiation. Greenhouse gases such as carbon dioxide, methane, and water vapour trap some of this outgoing heat, keeping the planet warm through the greenhouse effect.
3. Explain how climate change affects the water cycle. Illustrate with examples.
Solution
Climate change intensifies the water cycle by increasing evaporation due to rising temperatures. Warmer air can hold more water vapour, leading to changes in rainfall patterns.
Effects of Climate Change on the Water Cycle
- Increased evaporation from oceans, lakes and rivers: For example, rising global temperatures increase evaporation from water bodies, adding more water vapour to the atmosphere.
- More intense rainfall and flooding in some regions: For example, parts of India experience severe floods due to unusually intense monsoon rainfall.
- Longer droughts in other regions: For example, some areas face prolonged dry periods because they receive reduced or irregular rainfall.
- Faster melting of glaciers and snow: For example, Himalayan glaciers are melting at an accelerated rate due to increasing atmospheric temperatures
4.Describe how albedo affects the Earth's surface temperature and its climate.
Solution
Albedo is the fraction of sunlight reflected by the surface. Surfaces with high albedo (snow, ice, clouds) reflect more sunlight and remain cooler. Surfaces with low albedo (forests, oceans, dark soil) absorb more sunlight and become warmer. Thus, albedo influences local and global temperatures. Melting ice reduces Earth's albedo, causing more solar energy absorption and further warming, which contributes to climate change.
5. 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?
Solution
Valley Breeze (Daytime)
During the daytime, mountain slopes heat up faster than the valley floor. The air above the slopes becomes warm and rises upward, causing cooler air from the valley to move up the slopes and create a valley breeze.
Mountain Breeze (Night time)
During the night time, mountain slopes cool rapidly after sunset. The air above the slopes becomes cooler and denser, causing it to flow downhill into the valley, thereby creating a mountain breeze.
Yes, the temperature of the breezes would differ. A rocky mountain absorbs and loses heat more rapidly, producing relatively warmer breezes during the day and cooler breezes at night. In contrast, a grass-covered mountain remains comparatively cooler during the day and warmer at night because vegetation and moisture moderate temperature changes.
6. 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?
Solution
The troposphere is mainly responsible for weather phenomena because it contains most of the Earth's atmospheric gases and almost all of its water vapour. Uneven heating of the Earth's surface creates differences in temperature and air pressure within this layer, leading to the formation of winds, clouds, storms, and rainfall.
7. Explain the processes involved in the nitrogen cycle. How would life on Earth be affected if nitrogen were not cycled?
Solution
Processes involved in the Nitrogen Cycle are as follows:
- Nitrogen Fixation: Atmospheric nitrogen is converted into usable forms such as ammonia.
- Nitrification: Ammonia is converted into nitrites and nitrates by bacteria.
- Assimilation: Plants absorb nitrates and use them to make proteins.
- Ammonification: Decomposers convert dead organisms and waste into ammonia.
- Denitrification: Bacteria convert nitrates back into atmospheric nitrogen. If nitrogen were not cycled, plants would not obtain usable nitrogen needed for growth and protein synthesis. As a result, proteins and other essential biomolecules could not be produced, leading to the collapse of food chains and severely affecting life on Earth.
8.What are the impacts of deforestation on the Earth's oxygen and carbon cycles? What are the other consequences of deforestation?
Solution
Effects of Deforestation on the
(1) Oxygen Cycle: Reduced oxygen production- Trees release oxygen during photosynthesis. When forests are cut down, the amount of oxygen produced decreases, affecting the balance of gases in the atmosphere.
(2) Carbon Cycle: Reduced carbon dioxide absorption- Trees absorb carbon dioxide from the atmosphere during photosynthesis. Fewer trees mean less is removed from the atmosphere.
Release of stored carbon-When trees are cut down, burned, or decompose, the carbon stored in their tissues is released back into the atmosphere as carbon dioxide.
Increase in atmospheric levelsThe combined effect of reduced carbon absorption and increased carbon release raises the concentration of carbon dioxide in the atmosphere, enhancing the greenhouse effect.
Other consequences of deforestation:
(a) Loss of biodiversity: Forests provide habitats for numerous plants and animals. Deforestation destroys these habitats, leading to a decline in biodiversity.
(b) Soil erosion: Tree roots bind the soil and prevent it from being washed away. Without vegetation cover, the soil becomes more vulnerable to erosion by wind and water.
(c) Reduced rainfall: Trees release water vapour through transpiration, which contributes to cloud formation and rainfall. Deforestation can disrupt local and regional rainfall patterns.
(d) Increased flooding: Forests help absorb and store rainwater. Their removal increases surface runoff, making floods more frequent and severe.
(e) Habitat destruction: Many organisms lose their natural homes when forests are cleared, forcing them to migrate or face extinction.
(f) Climate change and global warming: Higher atmospheric levels trap more heat, contributing to global warming and long-term changes in climate patterns.
9. Explain with suitable diagram the path that carbon takes to go back to the atmosphere. You may start from plants using from the atmosphere.
Solution
Path of Carbon Back to the Atmosphere
- Atmospheric is absorbed by plants during photosynthesis and converted into food.
- Carbon enters animals when they feed on plants and becomes part of their bodies.
- Plants and animals release back into the atmosphere through respiration.
- Dead plants and animals decompose, releasing some carbon into the atmosphere and some into the soil.
- Over millions of years, buried organic matter forms fossil fuels such as coal, oil, and natural gas.
- Combustion of fossil fuels in industries, power plants, and vehicles releases stored carbon back into the atmosphere as .
- Some atmospheric is absorbed by oceans, where it is used by plankton and other marine organisms.
- dissolved in ocean water can return to the atmosphere, continuing the carbon cycle.
Thus, carbon continuously moves between the atmosphere, living organisms, oceans, and the Earth's crust, eventually returning to the atmosphere as carbon dioxide.
10.Why is an excess of in the atmosphere considered undesirable even though it is required by plants?
Solution
Although carbon dioxide ( ) is essential for photosynthesis and plant growth, an excess amount in the atmosphere is undesirable because of following:
- Excess strengthens the greenhouse effect by trapping more heat in the atmosphere.
- Increased heat causes global warming, raising the Earth's average temperature.
- Global warming leads to climate change, resulting in changes in weather patterns and more frequent extreme weather events.
- Higher temperatures melt glaciers and polar ice, causing sea levels to rise.
- Some excess dissolves in oceans, making seawater more acidic and causing ocean acidification.
- Ocean acidification harms marine life, especially corals, shellfish, and plankton. Therefore, a balanced concentration of is necessary to maintain a stable climate and healthy ecosystems.
11.How is heat lost from the surface of the Earth? What is its significance?
Solution
The Earth loses heat mainly by emitting infrared radiation from its surface into space. After absorbing solar energy during the day, the Earth's surface reradiates this energy as long-wave infrared radiation. Some of this heat escapes directly into space, while some is absorbed and re-emitted by greenhouse gases in the atmosphere. This continuous loss of heat helps regulate the Earth's temperature and prevents excessive warming.
Significance of heat loss from the surface
- Prevents excessive heating of the Earth: The release of heat into space prevents the continuous accumulation of solar energy, helping to keep the Earth's temperature within a liveable range.
- Maintains the Earth's energy balance:
The Earth receives energy from the Sun and loses energy through infrared radiation. This balance between incoming and outgoing energy helps maintain a relatively stable global temperature. 3. Supports stable climatic conditions:
Heat loss regulates atmospheric temperatures and contributes to the circulation of air and ocean currents, which influence weather and climate patterns around the world. 4. Makes life possible on Earth:
Without the continuous loss of heat, the Earth's surface would become excessively hot. The balance between heat gain and heat loss creates conditions suitable for the survival of plants, animals, and humans.
12. If the Earth were a flat disc instead of a sphere, how would the patterns of solar radiation and temperature be different?
Solution
If the Earth were a flat disc instead of a sphere, the distribution of solar radiation across its surface would be very different. Sunlight would fall much more uniformly over most of the surface. As a result, there would be far less variation in temperature between different regions.
The difference between equatorial and polar temperatures would be greatly reduced, and the distinct climate zones such as tropical, temperate, and polar regions would not develop in the same way.
The reduced temperature differences would also affect atmospheric circulation. Global wind systems, such as trade winds and westerlies, and major ocean currents would either be very different or may not form as they do today. Since these systems play a major role in distributing heat around the planet, weather patterns would also change significantly.
Furthermore, seasonal variations would be greatly altered because the distribution of solar energy throughout the year would differ from that on a spherical Earth. The variety of climates and ecosystems that exist today might not develop.
13. Suppose there is a rise in atmospheric temperature on Earth. How would this affect the cryosphere, hydrosphere and biosphere?
Solution
A rise in atmospheric temperature would affect all the major spheres of the Earth.
Cryosphere:
Glaciers, ice caps, and polar ice sheets would melt faster due to rising temperatures, reducing the amount of ice stored on Earth. At the same time, snow cover would decrease, exposing darker land and water surfaces that absorb more solar energy instead of reflecting it, which further accelerates global warming.
Hydrosphere: Rising temperatures would cause glaciers and polar ice to melt, leading to a rise in sea levels and increasing the risk of flooding in coastal regions. Higher temperatures would also intensify the water cycle, resulting in more frequent floods in some areas and prolonged droughts in others due to changes in rainfall patterns. In addition, warmer ocean waters would affect marine ecosystems and contribute to coral bleaching.
Biosphere:
Rising temperatures would alter habitats and make some environments unsuitable for the plants and animals living there. As a result, many species would migrate to cooler regions or higher altitudes in search of favourable conditions. However, not all organisms would be able to adapt or migrate quickly enough, leading to a decline in biodiversity and an increased risk of extinction for many species.
14. Explain how the Earth's atmosphere helps in maintaining a suitable temperature for life to survive on the Earth.
Solution
The atmosphere acts like a protective blanket around the Earth and helps maintain a temperature suitable for life in the following ways:
- It allows solar radiation to reach the Earth's surface, providing the energy needed to warm the planet and support processes such as photosynthesis and the water cycle.
- Greenhouse gases in the atmosphere trap a portion of the outgoing heat, preventing all of it from escaping into space and keeping the Earth warm enough for living organisms.
- It prevents extreme temperature variations between day and night. Without the atmosphere, days would be extremely hot and nights extremely cold, making survival difficult for most forms of life.
- It distributes heat through winds and weather systems, transferring energy from warmer regions to cooler regions and helping to maintain a more balanced global climate. Thus, the atmosphere regulates the Earth's temperature and creates environmental conditions that are favourable for the survival of plants, animals, and humans.
15.Describe the interrelationship between different spheres of the Earth. Illustrate with example how these spheres function in a delicate balance
Solution
The Earth's spheres are closely interconnected and constantly interact with one another. The atmosphere consists of air and gases, the hydrosphere includes all water bodies, the geosphere comprises rocks, soil, and landforms, the biosphere contains all living organisms, and the cryosphere includes ice, snow,
and glaciers. Together, these spheres form a complex Earth system that supports life.
Example to show delicate balance of spheres: Water Cycle
Water evaporates from oceans, lakes, and rivers (Hydrosphere) into the Atmosphere.
In the atmosphere, the water vapour cools and condenses to form clouds, which eventually produce rainfall.
Rainwater enters the soil and flows through rivers (Geosphere and Hydrosphere).
Plants absorb water from the soil, and animals use it for survival (Biosphere).
Some water is stored as snow and glaciers (Cryosphere), which act as important freshwater reservoirs.
Thus, the Earth's spheres function together in a delicate balance. Any disturbance in one sphere, such as melting glaciers, deforestation, or pollution, can affect the other spheres and disrupt the overall stability of the Earth system.
4.0 Important Key Concepts of NCERT Solutions for Class 9 Science Chapter 13
5.0Quick Revision on Class 9 Science Chapter 13 Earth as a System: Energy, Matter and Life
6.0Related Study Materials Class 9 Science
ALLEN’s study materials are made according to the latest NCERT syllabus and CBSE curriculum. These study materials will help you to boost your Class 9 Science preparation. Refer NCERT Solutions, NCERT Textbooks, Revision Notes, Sample Papers and Previous Years’ Question Papers to build strong concepts, practise regularly and revise the important topics with confidence.
7.0 Advantages of Chapter 13 Science Class 9 NCERT Solutions
- Explains Earth's Systems: Helps students understand how the atmosphere, hydrosphere, geosphere, biosphere, and cryosphere are interconnected.
- Strengthens Energy Flow Concepts: Simplifies how solar energy drives Earth's natural processes and supports life.
- Clarifies Matter Cycles: Explains the water, carbon, nitrogen, and oxygen cycles in a simple and structured manner.
- Develops System Thinking: Shows how energy and matter move continuously through Earth's systems.
- Builds Environmental Awareness: Highlights the impact of human activities on Earth's systems and the importance of sustainability.