---
title: "NCERT Solutions Class 9 Science Earth as a System: Energy, Matter, and Life"
url: https://www.swavid.com/science/class/9/chapter/earth-as-a-system-energy-matter-and-life/ncert-solutions
dateModified: 2026-10-07T16:39:19+00:00
---

# NCERT Solutions Class 9 Science Earth as a System: Energy, Matter, and Life

This chapter's questions cover the interconnected Earth spheres, energy balance, biogeochemical cycles, and the impacts of human activities on the Earth system. They test students' understanding through conceptual queries, calculations, and analytical problems.

Free PDF (16 pages): https://www.swavid.com/api/seo/pdf/ncert/science/class-9/swavid-ncert-solutions-class-9-science-chapter-13-earth-as-a-system-energy-matter-and-life-19a5426430.pdf

## Think It Over

### Question 1

*3 marks · Short answer*

How does the warming of Arabian Sea water affect the southwest monsoon in India?

**Solution**

1. Warmer Arabian Sea water leads to increased evaporation from the sea surface.
2. This enhanced moisture and evaporation causes fluctuations in the southwest monsoon.
3. This results in variability in rainfall, bringing floods to some regions of India while leaving others in drought.

**Answer:** Warming of the Arabian Sea causes higher evaporation, leading to fluctuations in the southwest monsoon that result in heavy floods in some regions and droughts in others.

> Common mistake: Confusing increased evaporation with a uniform increase in rainfall across the entire country.

### Question 2

*3 marks · Short answer*

If a large forest is cleared, how can that affect the flow of a river in that area?

**Solution**

1. Clearing a large forest reduces transpiration and local rainfall, and removes tree roots that hold the soil together.
2. Loss of tree cover and roots decreases water infiltration into the ground, reducing groundwater recharge.
3. This results in increased surface run-off during rains, causing sudden high flows or floods, and very low river flows during dry months.

**Answer:** Clearing a forest reduces soil infiltration and groundwater recharge, leading to increased surface run-off, soil erosion, and irregular river flows with floods during rains and dry river beds later.

> Common mistake: Stating that clearing a forest only affects trees without linking it to the water cycle and river flow.

### Question 3

*3 marks · Short answer*

What might happen to coastal cities in India if glaciers and polar ice keep melting faster?

**Solution**

1. Faster melting of glaciers and polar ice adds large amounts of water to the hydrosphere, raising sea levels.
2. Higher sea levels lead to the frequent flooding of low-lying coastal regions.
3. In the long run, this threatens coastal cities in India (such as Mumbai and Chennai) and causes habitat loss in coastal ecosystems.

**Answer:** Melting glaciers and polar ice increase sea levels, which can lead to the flooding of low-lying coastal regions and threaten coastal cities in India.

> Common mistake: Forgetting to mention the link between melting ice in the cryosphere and rising sea levels in the hydrosphere.

### Question 4

*3 marks · Short answer*

How would increasing carbon dioxide levels in the atmosphere affect the ocean plankton?

**Solution**

1. Increasing carbon dioxide levels in the atmosphere lead to increased absorption of CO2 by ocean water.
2. This makes sea water more acidic, disrupting marine chemistry and ecosystems.
3. Increased ocean acidity threatens tiny ocean plankton and coral reefs, which depend on stable carbonate ion concentrations.

**Answer:** Increasing atmospheric carbon dioxide increases ocean absorption, making sea water more acidic, which threatens tiny ocean plankton and disrupts marine ecosystems.

> Common mistake: Assuming carbon dioxide is only harmful in the atmosphere without considering its effect on ocean acidity.

## Activity 13.1: Let us explore

### Question 1

*Activity*

Observe 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.

**Solution**

1. Observe Fig. 13.1 showing various features of the Earth's surface.
2. Identify and circle solid rocks or landforms for the geosphere, a lake or river for the hydrosphere, snow or glaciers for the cryosphere, clouds or sky for the atmosphere, and trees, grass, or animals for the biosphere.

**Answer:** Examples representing the geosphere, hydrosphere, cryosphere, atmosphere, and biosphere can be identified and circled from Fig. 13.1.

### Question 2

*3 marks · Short answer*

How does snow (cryosphere) eventually become part of the lake (hydrosphere)?

**Solution**

1. Snow in the cryosphere accumulates in mountainous regions as ice and snow.
2. When temperatures rise, this snow melts into water.
3. The melted water flows down as runoff into rivers and streams, which eventually collect into lakes belonging to the hydrosphere.

**Answer:** Snow melts due to temperature rise and flows down as runoff into rivers and streams that feed into lakes, thereby becoming part of the hydrosphere.

> Common mistake: Confusing the cryosphere with the hydrosphere without explaining the process of melting and runoff.

### Question 3

*3 marks · Short answer*

If 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?

**Solution**

1. Less snowfall during winters leads to reduced water supply from melting snow in summers.
2. Consequently, the water level in the lake (hydrosphere) will decrease.
3. Reduced water availability will negatively impact the growth of grass (biosphere), thereby decreasing the food available for sheep.

**Answer:** The lake's water level will decrease due to less melting snow, which in turn will reduce the growth of grass needed to feed the sheep.

> Common mistake: Failing to connect the decrease in lake water to the resulting lack of moisture for grass growth.

### Question 4

*3 marks · Short answer*

Discuss with your classmates and write down how all the spheres are interconnected, and how a disturbance in one can lead to changes in others.

**Solution**

1. All the spheres of the Earth—geosphere, hydrosphere, cryosphere, atmosphere, and biosphere—are closely interconnected through the continuous flow of matter and energy.
2. A disturbance in one sphere alters this balance and triggers cascading changes in the other spheres.
3. For example, a change in the atmosphere (like global warming) affects the cryosphere (melting glaciers), which alters the hydrosphere (raising sea levels) and harms the biosphere (habitat loss).

**Answer:** The Earth's spheres are interconnected through the flow of matter and energy, meaning a disturbance in any single sphere causes cascading changes across the other spheres.

> Common mistake: Describing spheres as isolated systems rather than emphasizing their continuous interaction.

## Pause and Ponder

### Question 1

*Activity*

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

**Solution**

1. This activity demonstrates how changing the concentration of greenhouse gases like carbon dioxide and methane in the atmosphere affects the Earth's surface temperature.
2. Expected observation: Increasing the concentration of greenhouse gases traps more outgoing infrared radiation, leading to an increase in the simulated surface temperature.

**Answer:** Increasing greenhouse gas concentration traps more heat and raises the surface temperature.

## Pause and Ponder

### Question 2

*3 marks · Short answer*

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

**Solution**

1. Mountain breezes bring cool, dense air down into the valleys during the night.
2. This flow helps regulate local temperature and maintains moisture conditions in hilly regions.
3. These conditions support soil health, crop growth, and overall agricultural activity in mountainous areas.

**Answer:** Mountain breezes benefit agriculture by regulating temperature, maintaining moisture, and supporting soil and crop health in valleys.

> Common mistake: Confusing mountain breezes with valley breezes or omitting their role in moisture regulation.

### Question 3

*3 marks · Short answer*

What 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?

**Solution**

1. Warm equatorial surface waters travel over the ocean surface toward the poles as warm ocean currents.
2. As they move to higher latitudes, they release heat and moderate the climate of coastal and high-latitude regions.
3. This moderating influence keeps many ports ice-free during winter and supports human activities and marine ecosystems.

**Answer:** Warm water flowing toward the poles releases heat, moderates climate, keeps high-latitude ports ice-free, and supports ecosystems.

> Common mistake: Forgetting that ocean currents transport heat across latitudes to regulate global temperature differences.

## Pause and Ponder

### Question 4

*3 marks · Short answer*

The $CO_2$ dissolved in the ocean is disturbed when the global temperature increases. What will happen to marine life?

**Solution**

1. When global temperature increases, warmer ocean water reduces the ocean's capacity to absorb carbon dioxide and causes dissolved carbon dioxide to be released.
2. Excess carbon dioxide absorbed by the oceans makes sea water more acidic.
3. This increased acidity and temperature threaten tiny plankton and coral reefs, disrupting marine ecosystems and causing habitat loss.

**Answer:** Warmer ocean water releases carbon dioxide and becomes more acidic, which threatens marine life such as plankton and coral reefs.

> Common mistake: Stating that colder water absorbs less carbon dioxide instead of warmer water.

## Pause and Ponder

### Question 5

*3 marks · Short answer*

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

**Solution**

1. Biogeochemical cycles ensure the continuous recycling of essential nutrients like water, carbon, nitrogen, and oxygen between biotic and abiotic components.
2. If these cycles stop, living organisms would run out of vital resources, leading to an immediate collapse of ecosystems and the extinction of life on Earth.
3. For example, without the carbon cycle, plants cannot perform photosynthesis to produce food, and without the water and nitrogen cycles, organisms would suffer from severe dehydration and lack of proteins for survival.

**Answer:** The stoppage of biogeochemical cycles would deplete essential nutrients like carbon, nitrogen, and water, causing an immediate collapse of ecosystems and the extinction of plants and animals.

> Common mistake: Students often explain only one cycle instead of considering how the disruption affects both plants and animals across multiple interconnected cycles.

## Pause and Ponder

### Question 6

*3 marks · Short answer*

Discuss 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?

**Solution**

1. Human activities such as the burning of fossil fuels for electricity, transport, and industry release large amounts of carbon dioxide into the atmosphere.
2. Deforestation reduces natural carbon sinks like forests, further increasing the concentration of greenhouse gases like carbon dioxide and methane.
3. As an individual, I would reduce greenhouse gas emissions by conserving energy, using public transport or renewable energy sources, and minimizing waste through reducing, reusing, and recycling.

**Answer:** Human activities increase greenhouse gases through burning fossil fuels and deforestation, while individuals can reduce emissions by conserving energy and adopting sustainable habits.

> Common mistake: Listing general pollution causes without linking them specifically to greenhouse gas sources like fossil fuels and deforestation.

## Revise, Reflect, Refine

### Question 1

*1 mark · MCQ*

Choose the most appropriate option to describe the role of biogeochemical cycles in an ecosystem.

- To provide food directly to all organisms.
- To recycle essential nutrients between biotic and abiotic components.
- To create new elements for use by living things.
- To remove pollutants and toxins from the organism.

**Solution**

1. Biogeochemical cycles involve the continuous cyclic movement of matter and energy between the abiotic and biotic components of the Earth.
2. This ensures that essential nutrients are recycled and remain available to support life.

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

> Common mistake: Students often confuse biogeochemical cycles with food chains that only transfer food directly.

### Question 2

*1 mark · MCQ*

Which of the following is primarily responsible for warming of the Earth?

- Solar radiation is immediately absorbed by carbon dioxide, which then releases it as heat.
- The atmosphere’s tiny particles absorb incoming solar radiation, which directly heats the Earth.
- The Earth’s surface absorbs solar radiation, which is then re-radiated and trapped by greenhouse gases.
- The Earth’s environment is heated only by the solar radiation reflected by the clouds.

**Solution**

1. The Earth's surface absorbs incoming solar radiation and re-radiates it back in the infrared region.
2. Greenhouse gases in the atmosphere trap this outgoing heat, keeping the Earth warm enough to support life.

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

> Common mistake: Students incorrectly think the atmosphere directly absorbs most incoming solar radiation to heat the Earth.

### Question 3

*3 marks · Short answer*

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

**Solution**

1. Climate change causes a warmer atmosphere that holds more moisture, leading to heavier rains and intensified monsoons in some areas and droughts elsewhere.
2. Melting glaciers add more water to rivers, raising sea levels in the long run and threatening coastal cities like Mumbai and Chennai.
3. Sudden bursts of intense rainfall result in more surface run-off that erodes soil and less infiltration, which reduces groundwater recharge and affects agriculture.

**Answer:** Climate change alters the water cycle by causing intense monsoons, droughts, melting glaciers, sea level rise, and reduced groundwater infiltration.

> Common mistake: Forgetting to mention the impact on groundwater infiltration and soil erosion.

### Question 4

*3 marks · Short answer*

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

**Solution**

1. The fraction of solar radiation reflected by a surface is called its albedo.
2. Surfaces with high albedo like snow and ice reflect a large proportion of incoming solar radiation, keeping polar regions very cold.
3. Surfaces with low albedo like black soil and ocean water absorb more solar radiation, making them relatively warmer.

**Answer:** High albedo surfaces reflect solar radiation and stay cool, whereas low albedo surfaces absorb it and become warmer, influencing regional climate.

> Common mistake: Confusing high albedo with high heat absorption.

### Question 5

*3 marks · Short answer*

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**

1. During the day, mountain slopes heat up faster than the valley floor, creating a low-pressure area so cooler air moves up as a valley breeze; at night, slopes cool faster and dense air flows down as a mountain breeze.
2. Yes, the temperatures of the two mountain breezes would be different.
3. The mountain covered with barren rocks heats up and cools down faster than the grass-covered mountain, resulting in warmer daytime breezes and cooler nighttime breezes.

**Answer:** Mountain and valley breezes are caused by differential heating and cooling of slopes and valley floors; a barren rock mountain produces more extreme temperature variations in breezes than a grass-covered mountain.

> Common mistake: Not explaining how surface cover (rocks versus vegetation) affects the rate of heating and cooling.

### Question 6

*3 marks · Short answer*

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**

1. Nearly all weather phenomena like winds, storms, and rainfall take place in the troposphere.
2. The troposphere is heated from the Earth's surface, causing temperature to decrease with height.
3. As warm air rises in this layer, it drives winds, storms, and weather patterns.

**Answer:** The troposphere is the atmospheric layer responsible for weather phenomena, primarily because it is heated from the Earth's surface, causing warm air to rise and drive winds and storms.

> Common mistake: Confusing the troposphere with the stratosphere where the ozone layer is located.

### Question 7

*3 marks · Short answer*

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

**Solution**

1. The nitrogen cycle involves nitrogen fixation, assimilation, ammonification, nitrification, and denitrification.
2. Bacteria like Rhizobium convert atmospheric nitrogen into ammonia, which is converted into nitrites and nitrates by nitrifying bacteria and absorbed by plants.
3. If nitrogen were not cycled, plants and animals would not be able to synthesize essential proteins and nucleic acids, halting life on Earth.

**Answer:** The nitrogen cycle consists of nitrogen fixation, assimilation, ammonification, nitrification, and denitrification; without it, organisms cannot obtain nitrogen for proteins and nucleic acids, halting life.

> Common mistake: Forgetting to mention the key bacterial processes and specific nitrogen compounds involved.

### Question 8

*3 marks · Short answer*

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

**Solution**

1. Deforestation reduces photosynthesis, decreasing oxygen release and carbon dioxide absorption, thereby disrupting the oxygen and carbon cycles and increasing atmospheric CO2.
2. It leads to reduced transpiration, which can cause a decline in local rainfall and alter surface albedo.
3. Without tree roots to hold the soil, soil erosion increases, destroying habitats and leading to a decline in biodiversity.

**Answer:** Deforestation disrupts carbon and oxygen cycles by reducing photosynthesis, decreases local rainfall through reduced transpiration, increases soil erosion, and destroys habitats.

> Common mistake: Only mentioning climate change while ignoring soil erosion and habitat loss.

### Question 9

*3 marks · Short answer*

Explain with suitable diagram the path that carbon takes to go back to the atmosphere. You may start from plants using $CO_2$ from the atmosphere.

**Solution**

1. Plants convert atmospheric carbon dioxide into glucose through photosynthesis.
2. Animals consume plants, and both plants and animals release carbon dioxide back into the atmosphere through respiration.
3. When organisms die, decomposers break down their organic matter, releasing carbon dioxide, and fossil fuels formed from buried organic matter release CO2 upon combustion.

**Answer:** Carbon from atmospheric CO2 is taken up by plants via photosynthesis, passed to animals, and returned to the atmosphere through respiration, decomposition, and fossil fuel combustion.

> Common mistake: Omitting the role of decomposition and fossil fuel combustion in returning carbon to the atmosphere.

### Question 10

*3 marks · Short answer*

Why is an excess of $CO_2$ in the atmosphere considered undesirable even though it is required by plants?

**Solution**

1. Carbon dioxide is a greenhouse gas required in small amounts to trap outgoing heat and keep the Earth warm enough to support life.
2. Excess carbon dioxide intensifies the greenhouse effect, leading to global warming, melting of glaciers, rising sea levels, and extreme weather conditions.
3. It also increases ocean absorption, making sea water more acidic and threatening marine ecosystems.

**Answer:** Excess carbon dioxide enhances the greenhouse effect causing global warming, climate extremes, and ocean acidification, even though small amounts are needed to maintain habitable temperatures.

> Common mistake: Failing to explain why carbon dioxide is needed in the first place before discussing the ill effects of excess.

### Question 11

*3 marks · Short answer*

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

**Solution**

1. The Earth's surface absorbs solar radiation and re-radiates this heat back into the atmosphere in the infrared region.
2. Greenhouse gases absorb a portion of this outgoing heat, preventing it from escaping directly into space.
3. This balance of heat loss and retention maintains a suitable temperature for life and regulates the Earth's energy balance and climate.

**Answer:** Heat is lost as infrared radiation re-radiated from the Earth's surface; its significance lies in maintaining Earth's energy balance and keeping the planet warm enough for life.

> Common mistake: Stating that heat escapes completely into space without mentioning the trapping role of greenhouse gases.

### Question 12

*3 marks · Short answer*

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

**Solution**

1. On a spherical Earth, Sun's rays strike different latitudes at varying angles, concentrating insolation at the equator and spreading it over larger areas at the poles.
2. If the Earth were a flat disc facing the Sun, solar radiation would strike uniformly across the surface.
3. This would result in even heating across the disc, eliminating the temperature differences between the equator and poles that drive global winds and climate patterns.

**Answer:** A flat disc would receive uniform solar radiation across its surface, eliminating latitudinal temperature differences, seasons, and wind patterns caused by a spherical Earth.

> Common mistake: Ignoring how a flat surface changes the angle of incidence of solar rays compared to a sphere.

### Question 13

*3 marks · Short answer*

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

**Solution**

1. A rise in atmospheric temperature accelerates the melting of glaciers and polar ice in the cryosphere.
2. The melting ice adds more water to rivers and oceans in the hydrosphere, raising sea levels and threatening coastal cities.
3. This temperature increase disrupts ecosystems in the biosphere, leading to habitat loss, extreme weather conditions, and biodiversity loss.

**Answer:** A rise in atmospheric temperature causes melting of glaciers in the cryosphere, raises sea levels in the hydrosphere, and disrupts ecosystems leading to habitat loss in the biosphere.

> Common mistake: Stating the effect on only one or two spheres instead of covering the cryosphere, hydrosphere, and biosphere as asked.

### Question 14

*3 marks · Short answer*

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

**Solution**

1. The Earth's atmosphere partly absorbs incoming solar radiation and the ozone layer blocks harmful ultraviolet rays.
2. The Earth's surface absorbs sunlight and re-radiates it in the infrared region into the atmosphere.
3. Greenhouse gases like carbon dioxide, methane, and water vapour trap this outgoing heat, preventing it from escaping into space and keeping the Earth warm enough to support life.

**Answer:** The atmosphere maintains a suitable temperature by absorbing incoming solar radiation and using greenhouse gases to trap re-radiated infrared heat from the Earth's surface.

> Common mistake: Confusing incoming solar radiation absorption with the trapping of outgoing infrared heat by greenhouse gases.

### Question 15

*3 marks · Short answer*

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

**Solution**

1. The Earth functions as an interconnected system where matter and energy continuously move and interact across its spheres: geosphere, hydrosphere, cryosphere, atmosphere, and biosphere.
2. A disturbance in one sphere leads to changes in others, maintaining a delicate environmental balance.
3. For example, less snowfall in winters (cryosphere/atmosphere) leads to less water in lakes during summers (hydrosphere), resulting in insufficient water for grass growth and supporting sheep (biosphere).

**Answer:** The Earth's spheres are interconnected through the continuous flow of energy and matter, where a disturbance in one sphere directly causes changes in the others.

> Common mistake: Failing to illustrate the interrelationship with a concrete example involving multiple spheres.

## The Journey Beyond

### Question 1

*5 marks · Long answer*

Consider 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?

**Solution**

1. On Earth, uneven heating between the equator and poles creates global pressure belts, which are modified by the presence of both land and sea masses.
2. On a planet entirely covered by oceans, there would be no land-water differential heating or irregular surface friction, resulting in smooth, continuous, and well-defined planetary wind belts.
3. On a planet entirely covered by land, high surface friction and rapid heating and cooling of land masses would disrupt smooth wind flow, creating intense local pressure variations and erratic wind patterns.
4. Compared to Earth, the water-only planet would have steadier and more zonal winds, while the land-only planet would experience more extreme and disrupted wind circulation due to lack of moderating ocean currents.

**Answer:** The water-only planet would have smooth, uniform wind belts, the land-only planet would have disrupted and extreme wind patterns, whereas Earth has a moderate combination influenced by both land and sea distributions.

> Common mistake: Confusing local winds like land and sea breezes with global planetary wind circulation.

### Question 2

*5 marks · Long answer*

Choose 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.

**Part (i)**

1. Plants absorb carbon dioxide from the atmosphere and use sunlight during photosynthesis to synthesize glucose and other organic compounds.
2. The carbohydrates and organic matter in the meal items are built from these plant-derived carbon molecules.

Answer (i): Carbon in the meal originally came from atmospheric carbon dioxide fixed by plants through photosynthesis.

**Part (ii)**

1. Atmospheric nitrogen gas is converted into soluble nitrogen compounds in the soil by nitrogen-fixing bacteria like Rhizobium or through the industrial Haber-Bosch process used in making fertilisers.
2. Plants absorb these nitrates and ammonium compounds through their roots to build proteins, which are then consumed as food.

Answer (ii): Nitrogen entered the plants from the soil as nitrates fixed by bacteria or fertilisers produced via the Haber-Bosch process.

**Part (iii)**

1. Human activities such as burning fossil fuels for transporting food ingredients, using LPG or electricity for cooking, and manufacturing agricultural fertilisers release extra carbon dioxide and nitrogen oxides into the environment.

Answer (iii): Cooking, transportation, and industrial fertiliser production add extra greenhouse gases and nitrogen pollutants to the environment.

**Answer:** Main meal items obtain carbon via photosynthesis from atmospheric carbon dioxide and nitrogen via soil absorption from nitrogen-fixing bacteria or fertilisers, while cooking and transport add extra greenhouse gases.

> Common mistake: Forgetting to mention the Haber-Bosch process or bacterial fixation when explaining the source of nitrogen in crops.

### Question 3

*5 marks · Long answer*

Using 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?

**Solution**

1. Data from meteorological records generally shows increased variability in monsoon rainfall, marked by shorter durations of intense heavy rainfall (>50 mm) interspersed with dry spells.
2. A warmer Arabian Sea increases evaporation rates, loading the atmosphere with higher moisture content as explained in the chapter.
3. When this moisture-laden warm air moves over land, it results in sudden bursts of heavy rainfall rather than steady distributed rain.
4. Changes in land use, such as replacing forests and open land with concrete cities (urban heat island effect) and farms, alter local surface albedo and infiltration, worsening flooding during heavy downpours.

**Answer:** Observed trends of intense rainfall events are connected to increased moisture from a warmer Arabian Sea and altered land use patterns that disrupt local water cycles.

> Common mistake: Failing to link warmer ocean temperatures directly to higher atmospheric moisture capacity and heavier rainfall.

## Frequently asked questions

### How many questions are there in the Class 9 Science Chapter 13 NCERT solutions on SwaVid?

This chapter includes a total of 27 questions across various sections like Think It Over, Activities, Pause and Ponder, and Revise, Reflect, and Refine. SwaVid provides free PDF and step-by-step solutions for all these questions on this page only.

### What topics do the questions in this chapter cover?

The questions cover crucial concepts such as the interconnectedness of Earth's spheres, the greenhouse effect, biogeochemical cycles, and climate change impacts. They also explore practical scenarios like deforestation effects, melting glaciers, and ocean currents.

### Which are the most challenging question types in this chapter and how should I approach them?

The long-answer questions in The Journey Beyond and the analytical short answers in Revise, Reflect, and Refine are generally the hardest. To approach them for Class 9 exams, break down the core concepts like carbon cycles or planetary winds and structure your answer logically.

### How can I write answers to score full marks in Class 9 Science Chapter 13 exams?

To score full marks, ensure your answers use precise scientific terminology related to Earth's systems, energy flow, and matter cycling. Referring to SwaVid's step-by-step solutions available on this page will help you understand how to structure your responses effectively.

### Is the free PDF for these Class 9 Science solutions available for download?

Yes, you can access and download the free PDF and comprehensive step-by-step solutions for this new NCERT book chapter directly on this SwaVid page. These resources are tailored for the 2026-27 academic session based on the NCF 2023 guidelines.

## Related pages

- [Class 9 Science chapters](https://www.swavid.com/science/class/9)

Solutions written by SwaVid, a personal AI tutor for Class 6 to 10 Maths and Science. Practise this chapter free: https://www.swavid.com/start/student