NCERT Class 9 Science Chapter 13 Earth as a System: Energy, Matter, and Life

NCERT Class 9 Science Chapter 13 Earth as a System: Energy, Matter, and Life Solutions English Medium As Per New Syllabus. NCERT Class 9 Science Chapter 13 Earth as a System: Energy, Matter, and Life Notes to each chapter is provided in the list so that you can easily browse throughout different chapter NCERT Class 9 Science Chapter 13 Earth as a System: Energy, Matter, and Life Question Answer Download PDF and select needs one. CBSE Class 9 Science Textual Solutions.

NCERT Class 9 Science Chapter 13 Earth as a System: Energy, Matter, and Life

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Earth as a System: Energy, Matter, and Life

Chapter – 13

Pause And Ponder

1. Visit the website given below and study the effect of the concentration of greenhouse gas on surface temperature.

Ans: Increasing the concentration of greenhouse gases causes the Earth’s surface temperature to rise because more heat is trapped in the atmosphere. Decreasing the concentration of greenhouse gases lowers the surface temperature as less heat is retained.

Pause And Ponder

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

Ans: The cool mountain breeze lowers the temperature, reduces excessive evaporation, and helps maintain soil moisture, creating favourable conditions for the healthy growth of crops.

2. What happens to the warm surface of air from the equator as it travels toward the poles? What impact does this movement have on the area?

Ans: As the warm air from the equator moves towards the poles, it cools and sinks. This movement helps distribute heat across the Earth, influencing weather patterns and maintaining the global climate balance.

Pause And Ponder

1. The CO₂ dissolved in the ocean is disturbed if global temperature increases. What will happen to marine life?

Ans: As global temperature increases, the amount of dissolved CO₂ in seawater changes, affecting the carbon balance of the oceans. This disturbs marine ecosystems and can adversely affect many marine organisms, reducing biodiversity.

Pause And Ponder

1. What would happen to plants and animals on Earth if the biogeochemical cycles were disrupted and stopped? Explain by giving a few examples.

Ans: If biogeochemical cycles were disrupted, essential nutrients would not be recycled, affecting the survival of plants and animals. For example, the water cycle would stop rainfall, the carbon cycle would reduce photosynthesis, and the nitrogen cycle would decrease soil fertility, leading to the death of many living organisms.

Revise, Reflect, Refine

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.

Ans: (ii) To recycle essential nutrients between biotic and abiotic components.

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.

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

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

Ans: Climate change affects the water cycle because a warmer atmosphere holds more moisture, leading to heavier rains and intensified monsoons in some regions, while causing droughts in others. For example, melting glaciers add extra water to rivers, which can raise sea levels and threaten coastal cities like Mumbai and Chennai. Additionally, sudden bursts of intense rainfall increase surface run-off (which erodes soil) and decrease water infiltration, reducing the recharge of groundwater necessary for agriculture.

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

Ans: Albedo is the fraction of solar radiation reflected by a surface. High albedo surfaces, such as snow and ice, reflect a large proportion of incoming solar radiation, which keeps regions like the poles very cold. Conversely, low albedo surfaces, like black soil and ocean water, absorb more solar radiation and heat up quickly, making them relatively warmer. This differential reflection and absorption of solar energy significantly shape the Earth’s local temperatures and global climate patterns.

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?

Ans: Valley breezes form during the day when mountain slopes heat up faster than the valley floor; the warm air over the slopes rises, and cooler air from the valley moves up to replace it. Mountain breezes form after sunset when the mountain slopes lose heat faster than the valley floor; the cooler, denser air then flows down into the valley. Yes, the temperatures of the breezes from the two mountains would be different. Barren rocks and grass have different albedos and heat retention properties; barren rocks generally heat up and cool down much faster than vegetated areas. Therefore, the barren rock mountain would lose heat faster at night, producing a cooler and potentially stronger mountain breeze compared to the grass-covered mountain.

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?

Ans: The troposphere is the atmospheric layer mainly responsible for nearly all weather phenomena. The primary reason for this is that the troposphere is heated from the Earth’s surface, causing its temperature to decrease with height; as the warmed air near the surface rises, it drives the circulation of winds and the formation of storms.

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

Ans: The nitrogen cycle involves several steps to circulate nitrogen between the air, soil, water, and organisms. It begins with nitrogen fixation, where bacteria (like Rhizobium) convert atmospheric nitrogen gas into ammonia. Through nitrification, other bacteria convert this ammonia into nitrites and then nitrates. Plants absorb these compounds via assimilation, and animals get nitrogen by eating plants. When organisms die, decomposers return ammonia to the soil through ammonification. Finally, denitrification by bacteria converts nitrates back into atmospheric nitrogen gas. If nitrogen were not cycled, living organisms would not be able to synthesize essential biological molecules like proteins and nucleic acids, ultimately making survival and life on Earth impossible.

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

Ans: Deforestation heavily disrupts the carbon and oxygen cycles because clearing forests reduces the amount of plants available to perform photosynthesis; this leads to a decrease in oxygen production and saturates natural carbon sinks, leaving excess CO₂ in the atmosphere which intensifies global warming. Other severe consequences include reduced plant transpiration (which can decline local rainfall), altered surface albedo, increased soil erosion due to the lack of tree roots, and a massive loss of biodiversity as many species lose their natural habitats.

9. 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.

Ans: (Descriptive path of the carbon cycle): Plants first absorb CO₂ from the atmosphere and use sunlight to convert it into glucose during photosynthesis. 

From this point, carbon returns to the atmosphere through three primary paths:

(i) Respiration: Both plants and the animals that eat them break down glucose for energy and exhale CO₂ back into the air.

(ii) Decomposition: When plants and animals die, decomposers (bacteria and fungi) break down their organic matter, releasing CO₂ back into the atmosphere.

(iii) Combustion: Over millions of years, some buried dead plants and animals turn into fossil fuels (coal, oil, gas). When humans extract and burn these fossil fuels for energy, the stored carbon is rapidly released back into the atmosphere as CO₂.

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

Ans: While CO₂ is essential for plant photosynthesis and keeps the Earth warm enough to sustain life, an excess is undesirable because it intensifies the greenhouse effect, causing severe global warming. This excess heat leads to the melting of glaciers and Arctic sea ice, rising sea levels, and highly extreme weather conditions like intense monsoons or droughts. Furthermore, excess atmospheric CO₂ is absorbed by oceans, making the seawater more acidic, which threatens marine ecosystems, tiny plankton, and coral reefs.

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

Ans: The Earth’s surface loses heat by absorbing incoming sunlight and re-radiating it back upward in the form of infrared radiation. The significance of this process is that a portion of this outgoing infrared heat is trapped by greenhouse gases (like CO₂ and water vapour) in the atmosphere, creating the greenhouse effect which keeps the Earth warm enough for life to survive.

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

Ans: If the Earth were a flat disc, the Sun’s rays would strike its entire surface at the exact same angle. Because the Earth is spherical, solar radiation is concentrated over a smaller area at the equator and spread over a larger area at the poles, creating uneven heating. On a flat disc, this solar radiation would be distributed evenly across the surface, resulting in uniform heating and eliminating the vast temperature differences that currently drive the Earth’s global winds and ocean currents.

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

Ans: (i) Cryosphere: A rise in temperature would accelerate the melting of glaciers, snowcaps, and polar ice.

(ii) Hydrosphere: The melting ice would add excess water to oceans and rivers, raising sea levels and threatening coastal regions. It would also increase evaporation and moisture in the atmosphere, causing extreme weather patterns like heavier rainfall and floods in some areas and droughts in others.

(iii) Biosphere: These rapid environmental changes would disrupt ecosystems, leading to habitat loss for terrestrial and marine life, and threaten agricultural sustainability due to changing rainfall and soil erosion.

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

Ans: The atmosphere regulates the Earth’s temperature through two main actions. First, it partly absorbs and filters incoming solar radiation; for instance, the ozone layer in the stratosphere blocks harmful UV rays, while clouds absorb and scatter some sunlight. Second, it traps outgoing heat; the Earth’s surface re-radiates absorbed solar energy as infrared heat, and greenhouse gases (like CO₂, CH₄, and water vapour) in the atmosphere absorb this heat, preventing it from escaping completely into outer space. This greenhouse effect is what keeps the planet warm enough to sustain life.

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

Ans: The Earth’s spheres—geosphere, hydrosphere, cryosphere, atmosphere, and biosphere—are deeply interconnected through the continuous transfer of matter and energy (like the water and carbon cycles). For example, in the water cycle, water evaporates from oceans (hydrosphere) into the air (atmosphere), falls as snow on mountains (cryosphere) or rain on soil (geosphere), and sustains plants and animals (biosphere). A disruption in one sphere affects the others: if global warming increases the temperature of the Arabian Sea (hydrosphere), it alters evaporation and monsoon wind patterns (atmosphere), which causes irregular rainfall leading to floods or droughts on land (geosphere), ultimately threatening crop health and natural ecosystems (biosphere).