Question 1

Question 4State the important characteristics of each of the layers.

Accepted Answer

TroposphereIt is the lowermost atmospheric layer. Under normal conditions, the height of the troposphere is about 8 km at the Poles and about 18 km at the Equator.All weather phenomena takes place in this layer.In addition to pure air, it contains water vapour and dust.There is decrease in temperature with increasing altitude at the rate of 6.4° C per km in troposphere.Tropopause marks the upper boundary of troposphere.StratosphereThe lower most limit of stratosphere is at tropopause. It extends from 18 to 80 km.It is free from water vapour and dust.Temperature does not change with altitude. In certain situations slight increase in temperature (with elevation) may be noticed.No weather phenomena is seen accept Cirrus cloud formation in lower part.It has Ozone layer. There is a maximum concentration of ozone, a vital gas between 20-30 km.IonosphereIonosphere extends from 80 km to about 480 km.The ionisation of molecules and atoms occurs mainly as a result of ultraviolet rays, X-rays and gamma rays.The temperature decreases with increase in elevation until a low point of -100℃ is reached. Beyond this level, the temperature increases again as a result of absorption of short wave solar radiation by the atoms of oxygen.Nitrogen in the extremely rarified air of ionosphere.Ionosphere reflects low frequency radio waves, but absorbs medium and high frequency waves, making it especially important in long distance radio communication.ExosphereIt is the outermost layer of atmosphere.It contains rarified Hydrogen and Helium gases.

Question 2

Question 10Give the properties of Ionosphere.

Accepted Answer

IonosphereIonosphere extends from 80 km to about 480 km.The ionisation of molecules and atoms occurs mainly as a result of ultraviolet rays, X-rays and gama rays.The temperature decreases with increase in elevation until a low point of -100℃ is reached. Beyond this level, the temperature increases again as a result of absorption of short wave solar radiation by the atoms of oxygen.Nitrogen in the extremely rarified air of ionosphere.Ionosphere reflects low frequency radio waves, but absorbs medium and high frequency waves, making it especially important in long distance radio communication.

Question 3

Question 12What do you mean by 'Global Warming'? What are the consequences of 'Global Warming'?

Accepted Answer

The gradual increase in average temperature of the Earth and change in climate pattern is called Global warming. It occurs due to greenhouse effect of gases like carbon dioxide, methane and CFCs.The consequences of 'Global Warming' are:Melting of ice caps and Glaciers.Increasing sea temperature is wiping out coral reefs. These are breeding ground for many marine species and they protect coastlines from storms.It may pose serious threat to the ecological balance.Higher wildlife extinction rates.Higher sea levels.Global warming is increasing the frequency and severity of many types of disasters, including storms, heat waves, floods, and droughts.

Question 4

Question 13Name a few measures that could be taken to save the ozone layer.

Accepted Answer

A few measures that could be taken to save the ozone layer are:Minimize the emission of gases that are harmful for Ozone layer such as nitrogen oxide.Minimize the continuous release of synthetic chemicals primarily chlorofluoro-carbons (CFCs) into the atmosphere.Worldwide awareness against the use of Chloro-fluoro carbons.Illegal trade of harmful chemicals must be controlled.Finally, take strict decision to ban the use of harmful chemicals and invent alternatives to these chemicals.

Question 5

Question 14Name the three realms of the Earth.

Accepted Answer

Three realms of earth are:LithosphereHydrosphereAtmosphere.

Question 6

Question 15State the composition of the Earth's atmosphere.

Accepted Answer

The atmosphere consists of a number of gases like Nitrogen (78%), Oxygen (21%), Carbon dioxide and other gases like Argon, Helium etc. In addition to these gases, the atmosphere also contains water vapour and dust particles.

Question 7

Question 16How can we reduce global warming?

Accepted Answer

Following are the steps that can be taken to reduce global warming:Conservation of forests and control indescriminate felling of treesReduce industrial and vehicular pollution.Control the release of chlorofluoro carbons in atmosphere.Reduce the release of green house gases like carbon dioxide and methane.Create awareness regarding pollution and its effects.

Question 8

Question 11Assertion (A): About 90 per cent of the mass of air lies within a height of about 20 km from the surface of the earth.Reason (R): The air of the lower layer is always heavier or denser, while the upper layers are thinner or less dense.Both A and R are true and R is the correct explanation of A.Both A and R are true but R does not explain A.A is true but R is false.A is false but R is true.

Accepted Answer

Both A and R are true and R is the correct explanation of A.Explanation — In atmosphere, there are concentric layers of air, each layer having different density. The upper layers press down the lower ones. So, the air of the lower layer is always heavier or denser due to which about 90 per cent of the mass of air lies within a height of about 20 km from the surface of the earth.

Question 9

Question 17Name the layer which contains ions electrically charged particles which create a sheet like display of light known as Aurora Borealis in the northern hemisphere.IonosphereExosphereStratosphereMesosphere

Accepted Answer

Ionosphere

Question 10

Question 18Assertion (A): The troposphere is heated more from below than from above.Reason (R): The troposphere is heated by the incoming solar energy.Both A and R are true and R is the correct explanation of A.Both A and R are true but R does not explain A.A is true but R is false.A is false but R is true.

Accepted Answer

A is true but R is false.Explanation — The troposphere is not directly heated by incoming solar energy as incoming solar energy directly heats the earth's surface more than the air. The earth's surface absorbs solar radiation and then re-radiates heat upward, warming the troposphere from below.

Question 11

Question 19Which amongst the following is not a direct impact of Global Warming?Precipitation ChangeRadiation BalanceRise in Sea LevelDiseases

Accepted Answer

Radiation Balance

Question 12

Question 7What is known as Ozone Layer? What is leading to depletion of Ozone Layer in the atmosphere?

Accepted Answer

Ozone layer is a layer in the stratosphere of the atmosphere which keeps temperature constant in the lower levels and absorbs ultraviolet rays of the Sun.Many chemicals like Chlorine, Bromine and Chlorofluorocarbons are leading to depletion of Ozone Layer in the atmosphere. Chlorofluorocarbon compounds escape into the atmosphere and finally break down in the Stratosphere. They produce Chlorine atoms which destroy the Ozone layer.Sulphur dioxide given out during volcanic eruptions, solar storms and human activities also lead to depletion of Ozone layer.

Question 13

Question 8What would be the effect of Ozone Layer depletion? List the natural causes of Ozone Layer depletion.

Accepted Answer

The effects of ozone layer depletion are as follows:Increased levels of harmful ultraviolet (UV) radiation reaching the Earth's surface.Ultraviolet radiation can lead to skin cancer, eye damage, cataracts and weakened immune systems.It can cause damage to marine ecosystems.Increased UV radiation can harm crops, leading to reduced agricultural productivity and food scarcity.It can affect biogeochemical cycles, including those of nitrogen, sulfur, and carbon.It can influence climate patterns, altering atmospheric temperatures and precipitation levels.The natural causes of ozone layer depletion are volcanic eruptions and solar flares.

Question 14

Question 1(c)Give a reason for each of the following:(i) We find it difficult to breathe when we climb mountains.(ii) The atmosphere is the most dynamic entity.(iii) All the weather phenomena takes place in the troposphere.

Accepted Answer

(i) We find it difficult to breathe when we climb mountains because the layers of atmosphere become thinner at high altitudes. This means that there is less pressure to push the air into the lungs and a lower percentage of Oxygen in the air. This makes it harder to breath.(ii) The atmosphere is the most dynamic entity because of its composition. Large masses of air are being moved up and down and across the surface of the Earth.(iii) The troposphere is characterised by regular decrease in temperature with altitude. This decrease in temperature is known as normal lapse rate. The average decrease is 1°C for every 166 metre altitude gain. This temperature variation is responsible for many turbulences which result in all weather phenomena taking place in the troposphere.

Question 15

Question 2(a)Describe the structure of the atmosphere based on the picture given below.

Accepted Answer

The atmosphere consists of concentric layers of air. On the basis of the characteristics of temperature and air pressure, it can be divided into four thermal layers — Troposphere, Stratosphere, Mesosphere and Thermosphere. The Thermosphere is divided into Ionosphere and Exosphere. The four layers are briefly described below:Troposphere — It is the lowermost and densest layer. Its height varies from 18 km at the Equator to 8 km at the Poles.Stratosphere — This layer lies above the Troposphere. It extends to a height of 50 km from sea level. The Ozone layer lies within the stratosphere. Ozone is generally found between the altitudes of 20 and 50 km.Mesosphere — This layer lies above the Stratosphere. It extends to a height of 80 km from ground level.Thermosphere — It lies above Mesosphere and consists of two parts:Ionosphere — It extends up to a height of about 400 km.Exosphere — It is the uppermost layer of the atmosphere. It lies between 400 to 1500 km above the earth.

Question 16

Question 2(b)Explain the factors responsible for depletion of Ozone in atmosphere.

Accepted Answer

The factors responsible for depletion of Ozone in atmosphere are-Chemicals like Chlorine and BromineChlorofluorocarbon gases used in refrigerators, aircraft and air conditioners. CFC compounds escape into the atmosphere and finally break down in the stratosphere, producing Chlorine atoms which destroy the Ozone layer.Sulphur dioxide given out during volcanic eruptions, speeds up destructive chemical reactions.Solar storms consist of coronal mass ejections and solar flares associated with explosions on the surface of the Sun. They also cause Ozone layer depletion.Human activities also result in Ozone layer depletion. Due to bitterly cold Antarctic winter, the stratospheric ice clouds promote the production of chemically active Chlorine and Bromine. This leads to Ozone destruction when sunlight returns in the Antarctic spring.

Question 17

Question 3(a)How does conversion of forest land into agricultural land cause global warming?

Accepted Answer

Conversion of forest land into agricultural land cause global warming in the following ways:Reduction of Carbon Dioxide Absorption: Forests absorb carbon dioxide (CO₂) from the atmosphere in large amount. When forests are cut down to create agricultural land, this ability to absorb CO₂ is reduced. As a result, more carbon dioxide remains in the atmosphere, which contributes to global warming.Release of Stored Carbon: When trees are cut and often burned to clear the land, the carbon stored in trees is released into the atmosphere in the form of carbon dioxide, further increasing the concentration of greenhouse gases. This extra CO₂ traps more heat and raises the Earth's average temperature.Thus, deforestation for agriculture both reduces CO₂ absorption and increases CO₂ emission, making it a major cause of global warming.

Question 18

Question 1Do you think any one layer of the atmosphere is more significant than the other layers? If yes, which one and why? If not, reasons to support your answer.

Accepted Answer

No single layer of the atmosphere can be considered more significant than the others. Each layer plays a unique and important role in the functioning of the Earth's atmosphere.All the layers of the atmosphere are interconnected and work together to create a balanced and supportive environment for life on Earth. The layers include the troposphere, stratosphere, mesosphere, thermosphere, and exosphere, each with distinct characteristics and functions.The troposphere, closest to the Earth's surface, is crucial for weather patterns and the sustenance of life. The stratosphere contains the ozone layer, which protects against harmful ultraviolet radiation. The mesosphere helps protect the Earth from meteoroids. The thermosphere is responsible for the absorption of solar radiation. The exosphere extends into space and allows gases to gradually dissipate.Therefore, all layers of the atmosphere are essential for maintaining a stable climate, protecting life from harmful radiation, facilitating weather patterns, and supporting the overall functioning of the Earth's ecosystem.

Question 19

Question 2How is atmosphere responsible for Global Warming? What changes human beings can make in their lifestyle to preserve the atmosphere and check Global Warming?

Accepted Answer

The atmosphere plays a significant role in global warming due to the greenhouse effect. Certain gases in the atmosphere, such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), trap heat from the sun, leading to an increase in the Earth's temperature.To preserve the atmosphere and mitigate global warming, humans can make the following lifestyle changes:Reduce Carbon Footprint — Minimize the use of fossil fuels by opting for sustainable transportation. Choosing energy-efficient appliances and renewable energy sources like solar or wind power will also help.Conserve Energy — Practice energy-saving habits such as turning off lights and appliances when not in use, using natural lighting, and optimizing heating and cooling systems.Promote Sustainable Agriculture — Support local and organic farming practices that minimize the use of chemical fertilizers and pesticides, reduce food waste, and prioritize sustainable food choices.Conserve Water — Use water efficiently by fixing leaks, employing water-saving devices, and practicing responsible water consumption habits.Adopt Waste Management Practices — Reduce, reuse, and recycle materials to minimize waste generation. Properly dispose of hazardous materials and support recycling initiatives.

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