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Earth as a System : Energy, Matter, and Life

CBSE · Class 9 · Science

NCERT Solutions for Earth as a System : Energy, Matter, and Life — CBSE Class 9 Science.

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41 Questions Solved · 11 Sections

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Think It Over

1How does the warming of Arabian Sea water affect the southwest monsoon in India?Show solution
Warm Arabian Sea water causes more evaporation from the sea. This leads to fluctuations in the southwest monsoon, causing variability in rainfall in India. Some regions may get floods, while others may face drought.

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2If a large forest is cleared, how can that affect the flow of a river in that area?Show solution
Clearing a large forest reduces transpiration and can lead to a decline in local rainfall. It also increases soil erosion because tree roots no longer hold the soil together. As a result, the river flow may become less steady and the area may lose water more quickly.

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3What might happen to coastal cities in India if glaciers and polar ice keep melting faster?Show solution
If glaciers and polar ice melt faster, sea level will rise. This can cause flooding of low-lying coastal regions and threaten coastal cities in India such as Mumbai and Chennai.

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4How would increasing carbon dioxide levels in the atmosphere affect the ocean plankton?Show solution
Higher carbon dioxide levels can change ocean conditions. The chapter says that excess atmospheric $
\mathrm{CO}_2$ increases ocean absorption, making seawater more acidic, which can threaten tiny plankton and disturb marine ecosystems. Since plankton are important for the food chain, their decline would affect many ocean organisms.

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Activity 13.1: Let us explore

1Observe the features of the Earth as shown in Fig. 13.1. Identify and circle one example representing each of the geosphere, hydrosphere, cryosphere, atmosphere, and biosphere.Show solution
One should identify one example of each sphere from Fig. 13.1:
- Geosphere: rocks/land
- Hydrosphere: lake
- Cryosphere: snow
- Atmosphere: air/clouds
- Biosphere: grass, sheep or other living organisms

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2How does snow (cryosphere) eventually become part of the lake (hydrosphere)?Show solution
Snow in the cryosphere melts when temperatures rise. The meltwater flows downhill and collects in the lake, so the snow eventually becomes part of the hydrosphere.

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3If there is less snowfall during winters for a few years, how would this affect the lake's level and the grass available for the sheep?Show solution
Less snowfall means less meltwater reaching the lake in summer, so the lake level would fall. With less water available, the growth of grass would also reduce, so the sheep would have less grass to graze on.

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4Discuss with your classmates and write down how all the spheres are interconnected, and how a disturbance in one can lead to changes in others.Show solution
The spheres of the Earth are interconnected through the movement of energy and matter. For example, sunlight heats land and water, causing evaporation and winds; water returns as rain and supports plants and animals; plants take in carbon dioxide and release oxygen; rocks and soil supply minerals; and ice, water, air and living organisms all affect one another. If one sphere is disturbed, the others change too—for example, less snowfall can reduce lake water and grass growth, and warmer oceans can affect monsoon rainfall and glaciers.

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Ready to Go Beyond

1Visit the website given below and study the effect of the concentration of greenhouse gas on surface temperature, https://phet.colorado.edu/en/simulations/greenhouse-effectShow solution

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2The UV rays lie in the wavelength range of 100 nm100\,\mathrm{nm} to 400 nm400\,\mathrm{nm} [1 nanometre (nm) = 10−9 m10^{-9}\,\mathrm{m}] and have a much higher energy than the visible light. Prolonged exposure to these rays can damage the eyes and skin, and increase the risk of cancer. Therefore, people should use UV protective glasses and sunscreen if they are likely to be exposed to UV rays. UV rays are also useful in killing germs in water purifiers and help power fluorescent lights.Show solution

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Think as a Scientist

1An interesting estimation problem that helps us to appreciate the enormous amount of energy that we get from the Sun is to estimate how much of the Earth’s surface would be needed to be covered with solar panels to supply all the electric power that our country uses today (Fig. 13.4). To make this estimate, you can find these numbers on the internet, assume some insolation on the Earth’s surface and consider that some fraction of this energy is converted into electricity. You will probably find that even a fraction of the area of the Thar desert, if covered with solar panels, could supply India’s electricity needs.Show solution

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Activity 13.2: Let us find out

1Complete Table 13.1 using information from authentic sources like websites and books.Show solution

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Threads of Curiosity

1Urban Heat Island EffectShow solution

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6Why is the ozone layer so important?Show solution
The ozone layer is important because it acts as a protective shield by absorbing harmful UV radiation from the Sun. Without it, increased UV radiation could damage living organisms and ecosystems.

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Pause and Ponder

1How does the cool mountain breeze benefit agriculture activity, particularly the crops and soil?Show solution
A cool mountain breeze brings cooler air down the slopes at night. This helps agriculture by lowering temperature, reducing heat stress on crops, and helping maintain moisture and soil health. Such breezes can support better growing conditions in hilly regions.

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2What 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?Show solution
Warm equatorial surface water travels toward the poles and gradually cools. It then becomes denser and can flow back toward the equator through deeper ocean layers. This movement helps regulate climate by transporting heat from the equator to higher latitudes, reducing temperature differences across the planet.

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3The $
\mathrm{CO}_{2}$ dissolved in the ocean is disturbed when the global temperature increases. What will happen to marine life?Show solution
If global temperature increases, the ocean may absorb more carbon dioxide and become more acidic. This can threaten marine life, especially tiny plankton and coral reefs, and may disturb marine ecosystems.

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4What would happen to plants and animals on Earth if the biogeochemical cycles were disrupted and stopped? Explain by giving a few examples.Show solution
If biogeochemical cycles stopped, essential elements like carbon, nitrogen, oxygen and water would no longer be recycled. Plants would not get enough nutrients, so they would stop growing; animals would lose food and oxygen supply; decomposition and soil fertility would collapse. For example, without the carbon cycle plants could not continue photosynthesis properly, and without the nitrogen cycle proteins and nucleic acids could not be made efficiently. Life on Earth would eventually fail.

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5Discuss 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?Show solution
Human activities increase greenhouse gases mainly by burning fossil fuels, deforestation, industrial emissions and vehicle exhaust. These add extra CO₂, methane and other gases to the atmosphere. As an individual, one can reduce emissions by saving electricity, using public transport or walking/cycling, planting trees, reusing and recycling, and avoiding unnecessary waste.

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Revise, Reflect, Refine

6Choose the most appropriate option to describe the role of biogeochemical cycles in an ecosystem.Show solution
Biogeochemical cycles move matter such as carbon, nitrogen, oxygen and water between the living (biotic) and non-living (abiotic) parts of the Earth. So the correct option is (ii).

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7Which of the following is primarily responsible for warming of the Earth?Show solution
The Earth is warmed because the surface absorbs solar radiation, then re-radiates it as infrared heat, and greenhouse gases trap part of this outgoing heat. So the correct option is (iii).

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3Explain how climate change affects the water cycle. Illustrate with examples.
4Describe how albedo affects the Earth's surface temperature and its climate.
5How 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?
6You 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?
7Explain the processes involved in the nitrogen cycle. How would life on Earth be affected if nitrogen were not cycled?
8What are the impacts of deforestation on the Earth's oxygen and carbon cycles? What are the other consequences of deforestation?
9Explain with suitable diagram the path that carbon takes to go back to the atmosphere. You may start from plants using CO2\mathrm{CO}_{2} from the atmosphere.
10Why is an excess of CO2\mathrm{CO}_{2} in the atmosphere considered undesirable even though it is required by plants?
11How is heat lost from the surface of the Earth? What is its significance?
12If the Earth were a flat disc instead of a sphere, how would the patterns of solar radiation and temperature be different?
13Suppose there is a rise in atmospheric temperature on Earth. How would this affect the cryosphere, hydrosphere and biosphere?
14Explain how the Earth's atmosphere helps in maintaining a suitable temperature for life to survive on the Earth.
15Describe the interrelationship between different spheres of the Earth. Illustrate with example how these spheres function in a delicate balance.
1(ii) 2. (iii)
2(iii)

The Journey Beyond

21Consider two hypothetical Earth-sized planets that have an atmosphere. Assume that one planet is entirely covered by oceans and the other is entirely by land. Knowing that the Sun heats the equator more than the poles, how would the wind patterns on these planets compare with the wind systems we observe on Earth, with its combination of land and sea?
22Choose any one meal you ate recently (it could be anything, for example, roti and dal, rice and sambar, idli and chutney, and so on). For each main item in the meal, find out and explain: (i) how the carbon in it originally came from carbon dioxide in the air through photosynthesis, and (ii) how the nitrogen in it likely came from the atmosphere into the soil (for example, by bacteria or through the Haber-Bosch process and fertilisers) and then into the plant. Further, list other human activities involved in producing or cooking this meal that add extra carbon dioxide or nitrogen to the environment.
23Using data from the India Meteorological Department (IMD, https://mausam.imd.gov.in/) or newspaper records, find the average monsoon rainfall (June–September, or the local season) for your city or district for 5 years during two decades, such as the 1980s and 2020s. Note any trend you may find (increasing or decreasing, or the total number of days) with heavy rain (>50 mm). How can this be connected to the warmer Arabian Sea temperatures or changes in land use (forests to farms to cities) as discussed in the chapter?

The Quest Continues ...

1New tools are allowing scientists to observe the planet in real time and uncover hidden connections between climate, ecosystems, and human activity. What new discoveries will these tools reveal about the changing Earth, and how will they improve our understanding of global warming and climate change?

Meet a Scientist

1K.R. Ramanathan,

India's atmospheric scientist, climbed to an

altitude of 18,000 feet in the Himalayas in 1934 to measure the ozone levels, and discovered that they were lower than expected. His work laid the foundation for understanding how UV absorption varies with altitude and pollution. Later on, he led early monsoon forecasting efforts.

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Frequently Asked Questions

What are the important topics in Earth as a System : Energy, Matter, and Life for CBSE Class 9 Science?
Earth as a System : Energy, Matter, and Life covers several key topics that are frequently asked in CBSE Class 9 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
How to score full marks in Earth as a System : Energy, Matter, and Life — CBSE Class 9 Science?
Understand the core concepts first, then work through the 71 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.
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This page has free step-by-step NCERT Solutions for every exercise question in Earth as a System : Energy, Matter, and Life (CBSE Class 9 Science) — written the way examiners award marks: given, formula, working, answer.

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