Introduction
NCERT Solutions for Class 9 Science Chapter 13, Earth as a System: Energy, Matter, and Life, help students understand Earth as an interconnected system in which energy, matter, and living organisms interact continuously. This chapter from the new NCERT textbook, Exploration: A Textbook of Science for Grade 9, brings together important ideas about Earth’s major components and the processes that connect them.
The solutions provide clear explanations for the questions and activities given in the textbook. Students can use them to understand the interactions between different Earth systems, revise important concepts, and prepare effectively for examinations.
NCERT Intext Solution
(For questions see the NCERT)
1. Question
Answer: Effect of Greenhouse Gas Concentration on Surface Temperature
After studying the simulation, we observe that:
- As the concentration of greenhouse gases increases, the Earth’s surface temperature also increases.
- Greenhouse gases such as carbon dioxide (CO₂), methane (CH₄), and water vapour trap more outgoing infrared radiation.
- This trapped heat remains in the atmosphere, causing the greenhouse effect.
- Higher greenhouse gas concentrations lead to greater warming of the Earth’s surface.
- If greenhouse gas levels decrease, more heat escapes into space, and the surface temperature decreases.
Conclusion
There is a direct relationship between greenhouse gas concentration and surface temperature: more greenhouse gases → more heat trapped → higher surface temperature. This is one of the main causes of global warming and climate change.
Observation Table
| Greenhouse Gas Concentration | Surface Temperature |
| Low | Lower |
| Moderate | Moderate |
| High | Higher |
Result: Increasing greenhouse gas concentration causes an increase in Earth’s surface temperature.
2. Question
Answer:
The cool mountain breeze lowers the temperature in valleys and agricultural fields during the night. This helps to:
- Reduce excessive evaporation of water from the soil.
- Maintain soil moisture for a longer time.
- Protect crops from heat stress.
- Create favourable conditions for plant growth.
Thus, cool mountain breezes help conserve water and improve crop health.
3. Question
Answer: Warm surface water from the equator moves towards the poles through ocean currents. As it travels, it gradually loses heat to the surrounding atmosphere and becomes cooler.
Impact:
- It transfers heat from warmer regions to colder regions.
- It moderates the climate of coastal areas.
- It helps maintain the Earth’s heat balance.
- It influences weather patterns and rainfall in many regions.
Therefore, ocean currents play an important role in regulating global climate.
4.Question
Answer: When global temperature increases, the balance of dissolved CO₂ in the oceans is disturbed. More CO₂ dissolves in seawater, making it more acidic (ocean acidification). This harms marine organisms such as corals, shellfish, and plankton, which find it difficult to form shells and skeletons. Coral reefs may bleach and die, and the entire marine food chain can be affected, leading to a decline in marine biodiversity and fish populations.
5. Question
Answer: Biogeochemical cycles recycle essential nutrients such as carbon, nitrogen, oxygen, and water. If these cycles were disrupted or stopped, life on Earth would be severely affected.
- Plants would not receive essential nutrients like nitrogen and carbon, so they would be unable to grow properly or carry out photosynthesis.
- Animals would suffer because plants are the primary source of food in most food chains.
- The water cycle would stop supplying fresh water, causing droughts and water shortages.
- The oxygen cycle would be disturbed, reducing the availability of oxygen needed for respiration.
- Dead plants and animals would not decompose properly, causing nutrients to remain locked in waste materials.
Examples:
- Without the nitrogen cycle, crops would become weak and soil fertility would decrease.
- Without the carbon cycle, plants could not obtain enough carbon dioxide for photosynthesis.
- Without the water cycle, rivers, lakes, and groundwater sources would eventually dry up.
Conclusion: Biogeochemical cycles are essential for maintaining life and ecological balance. If they stopped, ecosystems would collapse, and most plants and animals would not survive.
6.Question
Answer: Human activities such as burning fossil fuels, deforestation, industrialization, excessive use of vehicles, and agricultural practices increase the concentration of greenhouse gases like carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) in the atmosphere. These gases trap heat and contribute to global warming.
As an individual, I can reduce greenhouse gas emissions by:
- Using public transport, cycling, or walking whenever possible.
- Conserving electricity and using energy-efficient appliances.
- Planting and protecting trees.
- Reducing, reusing, and recycling waste.
- Avoiding unnecessary use of fossil fuels and adopting renewable energy sources.
NCERT Exercise Solution
(For questions see the NCERT)
1. Question
Answer: (ii) To recycle essential nutrients between biotic and abiotic components.
2. Question
Answer: (iii) The Earth’s surface absorbs solar radiation, which is then re-radiated and trapped by greenhouse gases.
3. Question
Answer:
Climate change increases global temperatures, causing more evaporation from oceans, lakes, and rivers. This leads to changes in rainfall patterns, more intense storms, floods, and droughts.
Examples:
- Heavy rainfall and flooding in some regions.
- Prolonged droughts in others.
- Faster melting of glaciers and polar ice caps.
4. Question
Answer:
Albedo is the reflecting power of a surface.
- High albedo surfaces (snow, ice) reflect more sunlight and remain cooler.
- Low albedo surfaces (forests, oceans) absorb more sunlight and become warmer.
Thus, albedo influences Earth’s temperature and climate by controlling how much solar energy is absorbed.
5. Question
Answer:
- Valley breeze: During the day, mountain slopes heat up faster than valleys. Warm air rises up the slopes, creating a valley breeze.
- Mountain breeze: At night, mountain slopes cool rapidly. Cooler air flows downhill into the valley, creating a mountain breeze.
Yes, the temperatures would differ.
- The barren rocky mountain heats and cools more quickly.
- The grass-covered mountain remains relatively cooler during the day and warmer at night due to vegetation and moisture.
6. Question
Answer:
The Troposphere is responsible for weather phenomena.
Reason:
- It contains most of the Earth’s air and water vapour.
- Temperature decreases with altitude, causing air circulation, cloud formation, rainfall, winds, and storms.
7. Question
Answer:
Processes:
- Nitrogen fixation: Atmospheric nitrogen is converted into usable forms by bacteria and lightning.
- Nitrification: Ammonia is converted into nitrites and nitrates.
- Assimilation: Plants absorb nitrates and use them to make proteins.
- Ammonification: Decomposers convert organic nitrogen into ammonia.
- Denitrification: Bacteria convert nitrates back into atmospheric nitrogen.
If nitrogen were not cycled:
- Soil fertility would decrease.
- Plants could not synthesize proteins.
- Food chains would collapse.
- Life on Earth would be severely affected.
8. Question
Answer:
Impacts on oxygen and carbon cycles:
- Reduced photosynthesis decreases oxygen production.
- Less carbon dioxide is absorbed by plants.
- More CO₂ accumulates in the atmosphere, enhancing global warming.
Other consequences:
- Loss of biodiversity.
- Soil erosion.
- Reduced rainfall.
- Increased floods and droughts.
- Habitat destruction.
9. Question
Answer
Atmospheric CO₂
↓
Photosynthesis
↓
Plants
↓
Animals eat plants
↓
Respiration by plants & animals
↓
Atmospheric CO₂
Dead plants & animals
↓
Decomposition
↓
Atmospheric CO₂
Fossil fuels
↓
Combustion
↓
Atmospheric CO₂
Carbon enters plants through photosynthesis and returns to the atmosphere through respiration, decomposition, and combustion.
10. Question
Answer:
Although plants require CO₂ for photosynthesis, excess CO₂ strengthens the greenhouse effect, causing:
- Global warming
- Climate change
- Melting glaciers
- Rising sea levels
- Extreme weather events
Therefore, excessive CO₂ is harmful to the environment.
11. Question
Answer:
The Earth loses heat mainly through:
- Radiation (infrared radiation to space)
- Conduction
- Convection
- Evaporation
Significance:
- Maintains Earth’s energy balance.
- Prevents excessive heating.
- Helps regulate climate and weather.
12. Question
Answer:
If Earth were a flat disc:
- Solar radiation would not be distributed as it is on a sphere.
- The centre would receive maximum sunlight and be very hot.
- The edges would receive less sunlight and be much colder.
- There would be no distinct climatic zones like tropical, temperate, and polar regions.
- Global weather and climate patterns would be very different.
13. Question
Answer:
A rise in atmospheric temperature would affect all Earth systems:
- Cryosphere (ice-covered regions): Glaciers, ice caps, and polar ice would melt faster, reducing ice cover.
- Hydrosphere (water bodies): Sea levels would rise due to melting ice and thermal expansion of water. Changes in rainfall patterns could lead to floods and droughts.
- Biosphere (living organisms): Habitats would change, affecting plants and animals. Some species may migrate, while others may become endangered or extinct.
Thus, global warming can disturb the balance of Earth’s systems.
14. Question
Answer: The atmosphere acts like a protective blanket around Earth.
- It allows sunlight to reach the Earth’s surface.
- Greenhouse gases trap some of the heat radiated by Earth, preventing excessive heat loss.
- It reduces extreme temperature differences between day and night.
- Clouds and atmospheric circulation help distribute heat around the globe.
As a result, Earth’s temperature remains suitable for the survival of living organisms.
15. Question
Answer: The four major spheres of Earth are:
- Atmosphere – air
- Hydrosphere – water
- Lithosphere – land
- Biosphere – living organisms
These spheres constantly interact with one another.
Example: Water Cycle
- Water evaporates from oceans (hydrosphere) into the atmosphere.
- It condenses to form clouds and falls as rain.
- Rainwater reaches the lithosphere (land) and rivers.
- Plants and animals (biosphere) use this water for survival.
Any disturbance in one sphere affects the others. For example, deforestation in the biosphere can reduce rainfall, affecting both the atmosphere and hydrosphere. This shows that Earth’s spheres function in a delicate balance and are closely interconnected.
Chapter Overview
Class 9 Science Chapter 13 – Earth as a System: Energy, Matter, and Life
Earth is not made up of isolated parts. Its atmosphere, water, land, and living organisms interact with one another through the continuous movement of energy and matter.
This chapter helps students understand Earth as a connected system and explores how different components influence one another. It also highlights the role of living organisms in Earth’s systems and how natural processes maintain interactions between the different components.
Use this section to explain the specific Earth-system concepts, cycles, processes, diagrams, and examples covered in the current NCERT textbook.