The Atmosphere

In which layer of the atmosphere is moisture available in sufficient quantities?

1. mesosphere
2. ionosphere
3. exosphere
4. troposphere

Answer

troposphere

Reason — The troposphere contains almost all the dust particles and water vapour present in the atmosphere, so moisture is available there in sufficient quantities. The mesosphere, ionosphere (thermosphere) and exosphere are upper layers far above the surface where water vapour is negligible.

It is the layer of the atmosphere that traps the terrestrial heat and helps the Earth to maintain optimum temperature.

1. troposphere
2. stratosphere
3. exosphere
4. mesosphere

Answer

troposphere

Reason — The troposphere acts as a blanket and traps terrestrial heat, thereby keeping the Earth warm during the night and helping it maintain an optimum temperature.

Which of the following devices release Ozone Depleting Substances (ODS)?

1. fire extinguisher, LPG cylinder
2. microwave oven, mobile phone
3. refrigerator, air conditioner
4. locomotives, bulldozers

Answer

refrigerator, air conditioner

Reason — ODS such as CFCs may be released from junk refrigerators and air conditioners. Therefore, refrigerator and air conditioner form the pair in which both devices can release ODS.

Arrange the following in order of the chemical process of ozone depletion.

a. Chlorine atom pulls one oxygen atom out.
b. Free oxygen atom hits one chlorine monoxide.
c. Free chlorine atom hits one ozone molecule.
d. UV rays cause chlorine atom to break away from CFC molecule.

Choose the right sequence from the following:

1. a, b, c, d
2. d, c, a, b
3. d, c, b, a
4. a, b, d, c

Answer

d, c, a, b

Reason — In the chemical process, UV rays first cause a chlorine atom to break away from the CFC molecule (d), the free chlorine atom then hits an ozone molecule (c), pulls one oxygen atom away from it (a), and finally a free oxygen atom hits the chlorine monoxide (b). This gives the correct sequence d, c, a, b.

Choose the incorrect statement regarding reduction of global warming.

1. Should reduce energy consumption.
2. Should utilise conventional energy resources.
3. Should encourage green cities.
4. Promote electric-run vehicles.

Answer

Should utilise conventional energy resources.

Reason — To reduce global warming we should switch over from conventional energy resources like fossil fuels to renewable sources of energy, so utilising conventional energy resources is the incorrect statement. Reducing energy consumption, encouraging green cities and promoting electric-run vehicles are all correct measures that help reduce global warming.

The main objective of the Montreal Protocol was

1. to increase global forest cover.
2. to reduce pollution of water bodies.
3. to lower the production of Ozone Depleting Substances.
4. to increase consumption of fossil fuels.

Answer

to lower the production of Ozone Depleting Substances.

Reason — The chief objective of the Montreal Protocol was to reach a global agreement to reduce the production of Ozone Depleting Substances (ODS).

The ozone layer helps in

1. preventing the ultraviolet rays from reaching the Earth.
2. preserving the optimum temperature of the Earth.
3. absorbing the polluting gases released by the Earth.
4. increasing the temperature on the Earth.

Answer

preventing the ultraviolet rays from reaching the Earth.

Reason — The ozone layer acts as a shield and absorbs harmful ultraviolet (UV) radiation from the Sun, preventing it from reaching the Earth.

Which of the following is the most abundant gas in the Earth's atmosphere?

1. oxygen
2. nitrogen
3. water vapour
4. ozone

Answer

nitrogen

Reason — Nitrogen is the most abundant gas, accounting for about 78 per cent of the total volume of the atmosphere. Oxygen makes up about 21 per cent, while water vapour and ozone are present only in small or trace amounts.

Choose the correctly matched pairs.

1. the troposphere–lowest layer
2. the stratosphere–layer of the middle atmosphere
3. the mesosphere–contains ozonosphere
4. the thermosphere–uppermost layer

Answer

the troposphere–lowest layer

Reason — The troposphere is correctly matched as the lowest layer of the atmosphere. The stratosphere is not the middle-atmosphere layer (that is the mesosphere), the ozonosphere lies within the stratosphere and not the mesosphere, and the uppermost layer is the exosphere, not the thermosphere.

Which of the following is the coldest atmospheric layer?

1. the troposphere
2. the mesosphere
3. the exosphere
4. the stratosphere

Answer

the mesosphere

Reason — The mesosphere is the coldest atmospheric layer, with the temperature dipping to about −90°C in some parts.

In which layer of the atmosphere do very-high-speed winds called jet streams blow?

1. the stratopause
2. the tropopause
3. the mesopause
4. the exopause

Answer

the tropopause

Reason — Very-high-speed winds called jet streams blow in the tropopause, which marks the upper limit of the troposphere.

Which layer of the atmosphere has traces of very light gases such as hydrogen, helium and oxygen?

1. the stratosphere
2. the troposphere
3. the exosphere
4. the thermosphere

Answer

the exosphere

Reason — The exosphere is the uppermost layer of the atmosphere. Its air is extremely thin and rarefied, and it contains traces of very light gases such as hydrogen, helium and oxygen.

Which of the following is NOT a cause of global warming?

1. burning fossil fuels
2. rearing farm animals
3. planting trees
4. using fertilisers

Answer

planting trees

Reason — Planting trees increases forest cover and absorbs carbon dioxide from the air, so it helps reduce global warming rather than cause it. Burning fossil fuels, rearing farm animals and using fertilisers all release greenhouse gases and are causes of global warming.

Which water-borne disease spreads during the heatwave in summer?

1. malaria
2. dengue
3. cholera
4. rabies

Answer

cholera

Reason — Cholera is a water-borne disease that spreads during the heatwaves in summer. Malaria and dengue are vector-borne diseases spread by mosquitoes, and rabies is spread through animal bites.

Match the following.

1. 1-A, 2-B, 3-C, 4-D
2. 1-D, 2-C, 3-B, 4-A
3. 1-C, 2-D, 3-B, 4-A
4. 1-B, 2-C, 3-A, 4-D

Answer

1-C, 2-D, 3-B, 4-A

Reason — Carbon dioxide is linked with deforestation, methane with paddy fields, nitrogen oxide with the use of chemical fertilisers, and ozone is transported from the ozone layer. Thus, the correct match is 1-C, 2-D, 3-B, 4-A.

Two statements are given in the question below as Assertion (A) and Reason (R). Read the statements and choose the appropriate option:

Assertion (A): Ozone hole lets in UV rays that cause skin cancer and cataract.

Reason (R): We must buy ozone-friendly products.

Choose the correct option

1. A is true but R is wrong.
2. A is false but R is true.
3. Both A and R are true but R is not the correct explanation of A.
4. Both A and R are true and R is the correct explanation of A.

Answer

Both A and R are true but R is not the correct explanation of A.

Explanation — The ozone hole does let in increased amounts of harmful UV rays that cause skin cancer and cataract, so A is true. Buying ozone-friendly products is a valid measure to prevent ozone depletion, so R is also true. However, R is only a preventive step and does not explain why the ozone hole causes these health problems, so R is not the correct explanation of A.

Assertion (A): The atmosphere is held in place by the gravitational force of our planet.

Reason (R): The atmosphere forms the vital gaseous realm of the Earth.

1. A is true, but R is false.
2. A is false, but R is true.
3. Both A and R are true, but R is not the correct explanation of A.
4. Both A and R are true, and R is the correct explanation of A.

Answer

Both A and R are true, but R is not the correct explanation of A.

Explanation — The atmosphere is indeed held in place by the gravitational force of the Earth, so A is true, and it does form the vital gaseous realm of the Earth, so R is also true. However, R only describes what the atmosphere is and does not explain why it stays in place, so R is not the correct explanation of A.

Assertion (A): The troposphere acts as a blanket protecting the Earth from the extreme heat during the day.

Reason (R): The troposphere traps terrestrial heat, thereby keeping the Earth warm during the night.

1. A is true, but R is false.
2. A is false, but R is true.
3. Both A and R are true, but R is not the correct explanation of A.
4. Both A and R are true, and R is the correct explanation of A.

Answer

Both A and R are true, but R is not the correct explanation of A.

Explanation — The troposphere protects the Earth from extreme heat during the day and traps terrestrial heat to keep it warm during the night. Both statements are true, but the Reason describes a different function of the troposphere and does not explain the Assertion.

Assertion (A): High temperatures lead to higher evaporation rate.

Reason (R): The occurrence of droughts affects crop production.

1. A is true, but R is false.
2. A is false, but R is true.
3. Both A and R are true, but R is not the correct explanation of A.
4. Both A and R are true, and R is the correct explanation of A.

Answer

Both A and R are true, but R is not the correct explanation of A.

Explanation — High temperatures do lead to a higher rate of evaporation, so A is true, and the occurrence of droughts does affect crop production, so R is also true. However, R speaks about the effect of droughts on crops and does not explain why high temperatures increase evaporation, so R is not the correct explanation of A.

Give reason — The troposphere protects the Earth from extremes of temperature.

Answer

The troposphere acts as a blanket that protects the Earth from extreme heat during the day. At night, it traps terrestrial heat radiated by the Earth and keeps the Earth warm. Thus, it protects the Earth from extremes of temperature.

Give reason — Stratosphere provides ideal flying conditions for aircraft.

Answer

The stratosphere is almost free from water vapour and therefore has no weather disturbances. Hence, there is little turbulence and it provides ideal flying conditions for aircraft.

Give reason — Meteors slow down and burn up when they enter the mesosphere.

Answer

Meteors experience friction with the atmospheric gases when they enter the mesosphere. The resulting frictional heat causes them to slow down and burn up before reaching the Earth's surface.

Give reason — Deforestation contributes to global warming.

Answer

Forests are a major carbon sink, as they absorb carbon dioxide from the atmosphere during photosynthesis. When forests are cleared through deforestation, the carbon dioxide level in the atmosphere increases. This extra carbon dioxide traps more heat in the atmosphere, leading to global warming.

Give reason — Incandescent light bulbs should be replaced by CFL bulbs.

Answer

CFL bulbs consume less energy than incandescent light bulbs. Therefore, replacing incandescent bulbs with CFL bulbs helps save electricity and reduce global warming.

Give reason — The mesosphere is the coldest atmospheric layer.

Answer

In the mesosphere, temperature decreases continuously with increase in height and reaches its lowest point near the mesopause, dipping to about −90°C in some parts. Therefore, the mesosphere is the coldest atmospheric layer.

Give reason — The Earth has an optimum temperature for all living beings.

Answer

Greenhouse gases such as carbon dioxide and water vapour trap some of the terrestrial heat radiated by the Earth and prevent it from escaping into outer space. This greenhouse effect maintains an optimum temperature for living beings on the Earth.

Give reason — The depletion of the ozone layer is one of the major environmental concerns.

Answer

The ozone layer shields the Earth from harmful ultraviolet (UV) radiation. Its depletion allows more UV rays to reach the Earth, causing health problems such as skin cancer and cataract and adversely affecting plants and aquatic life. Therefore, ozone depletion is a major environmental concern.

Define the following terms:

a. chlorofluorocarbon gases

b. ionosphere

c. greenhouse gases

d. global warming

Answer

a. Chlorofluorocarbon gases (CFCs) — These are gases used in refrigerators and in some aerosol containers. They damage the ozone layer of the Earth's atmosphere.

b. Ionosphere — The part of the thermosphere where atmospheric gases break up into electrically charged particles called ions is known as the ionosphere. These ions reflect radio waves back to the Earth and enable radio broadcasts and wireless communication.

c. Greenhouse gases — Greenhouse gases are gases in the air that have the ability to trap more heat than other gases. Common greenhouse gases include water vapour, carbon dioxide and methane.

d. Global warming — The gradual rise in global temperatures caused by a high concentration of heat-trapping gases in the atmosphere is called global warming.

Define atmosphere. Name the different layers of the atmosphere.

Answer

The atmosphere is made up of a mixture of gases that form a layer surrounding the Earth. It is held in place by the gravitational force of our planet and forms the vital gaseous realm of the Earth.

The five layers of the atmosphere are:

1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere (Ionosphere)
5. Exosphere

What are ions? Why is their presence in the atmosphere significant?

Answer

Ions are electrically charged particles formed when molecules of atmospheric gases break up in the thermosphere.

Their presence is significant because they reflect radio waves back to the Earth and enable radio broadcasts and wireless communication. This region of the thermosphere is known as the ionosphere.

Discuss how an ozone hole is created.

Answer

Certain human activities release CFCs and other Ozone Depleting Substances (ODS) into the atmosphere. These substances release chlorine, which destroys ozone through the following process:

1. UV radiation causes a chlorine atom to break away from a CFC molecule.
2. The free chlorine atom hits an ozone molecule.
3. The chlorine atom pulls one oxygen atom away from the ozone molecule, forming chlorine monoxide.
4. A free oxygen atom hits the chlorine monoxide.
5. Another free chlorine atom is released and continues to destroy more ozone.

Thus, repeated destruction of ozone causes the ozone layer to become thin and creates an ozone hole.

How can we replace the ODS-emitting accessories in our daily life and prevent escape of chlorine molecules?

Answer

We can replace the ODS-emitting accessories and prevent the escape of chlorine molecules in the following ways:

1. We should dispose of junk refrigerators, air conditioners and other electronic gadgets carefully, so that the CFCs in them do not escape into the atmosphere.
2. We should avoid using aerosols from spray cans, fire extinguishers and solvent cleaners that release ODS.
3. We should purchase products that are labelled 'ozone friendly' or 'CFC-free'.

Discuss the composition of the atmosphere.

Answer

The atmosphere is made up of a mixture of gases. Nitrogen is the most abundant gas and accounts for about 78 per cent of the total volume of the atmosphere. Oxygen forms about 21 per cent of the atmosphere. The remaining 1 per cent consists of minute quantities of various trace gases such as carbon dioxide, hydrogen, helium, ozone and argon.

In its lower layers, the atmosphere also contains varying amounts of water vapour and suspended solid particles such as dust, salt and pollen.

Discuss the importance and significance of the 3 Rs in bringing about sustainable development.

Answer

By following the 3Rs — Reduce, Recycle and Reuse — strategy, we can use natural resources judiciously for our growth as well as save them for the needs of future generations. This is called sustainable development.

1. Reduce: We must reduce the use of natural resources so that they do not get depleted.
2. Reuse: We must reuse resources instead of throwing them away after each use. Reuse conserves new resources and prevents old resources from entering the waste stream.
3. Recycle: We must recycle or convert waste materials into new products by physical and chemical processes. In this way, waste is reduced and resources are conserved.

Thus, the 3Rs help conserve natural resources and reduce waste, thereby promoting sustainable development.

Why are eco-cities or green cities ideal examples of cities today? Name some green cities of the world.

Answer

Eco-cities or green cities are urban areas that try to lessen the environmental impacts of urbanisation. They reduce waste, encourage recycling, lower emission levels and reduce air, water and soil pollution. Therefore, they are ideal examples of cities today.

Some notable green cities of the world are Oslo, Vancouver, Copenhagen, Amsterdam, Stockholm, Zurich, Essen, Sydney, Singapore and San Francisco.

Why are renewable sources of energy preferred over fossil fuels? Give two examples of renewable sources of energy.

Answer

Renewable sources of energy are preferred over fossil fuels because they are cheap, abundant and non-polluting. Burning fossil fuels such as coal and petroleum releases greenhouse gases like carbon dioxide and contributes to global warming. Switching to renewable sources helps decrease the emission of greenhouse gases.

Two examples of renewable sources of energy are:

1. Solar energy
2. Wind energy

Look at the given picture and answer the following questions.

a. What is happening in the given picture?

b. What is the impact of this on the oceans?

c. List any two measures to reduce this problem.

Answer

a. The given picture shows the melting of a glacier due to global warming.

b. Melting glaciers increase the volume of water in the oceans and contribute to a rise in sea level. This may lead to the submergence of low-lying coastal areas and islands.

c. Two measures to reduce this problem are:

1. We should decrease the emission of GHGs by reducing the burning of fossil fuels and switching over to renewable sources of energy such as wind, Sun, water and tides.
2. We should plant more trees to increase forest cover, which reduces the excessive release of carbon dioxide in the air.

Read the passage given below and answer the questions that follow:

Keeping a large number of farm animals such as goats, sheep and buffaloes also contributes to global warming. When farm animals digest their food, methane is produced in their stomach, which is released into the atmosphere through their dung.

By removing large sections of forest to expand farmland and raising farm animals instead, humankind further disturbs the delicate balance in nature by increasing the amount of methane in the atmosphere.

(a) How are farm animals responsible for global warming?

(b) How do modern farming methods contribute to global warming?

(c) What are the two other reasons for warming up of the atmosphere abnormally?

Answer

(a) Farm animals such as goats, sheep and buffaloes produce methane while digesting their food. This methane is released into the atmosphere through their dung. Since methane is a greenhouse gas, rearing a large number of farm animals contributes to global warming.

(b) Modern farming contributes to global warming when forests are cleared to expand farmland and when artificial nitrogen fertilisers are used. Deforestation increases the amount of carbon dioxide in the atmosphere, while the use of artificial nitrogen fertilisers increases the level of nitrogen oxide in the air.

(c) Two other reasons for the abnormal warming of the atmosphere are:

1. Burning of fossil fuels such as coal and petroleum in industries, power plants and vehicles, which releases large amounts of carbon dioxide.
2. Harmful emissions from industries and vehicles, which release gases such as oxides of nitrogen, sulphur and methane.