Living Science 2020 2021 for Class 6 Science Chapter 16 - Air Around Us

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The density of the blanket of air that surrounds us becomes thinner as we go up. 

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Air is a mixture and not a compound. This is because air consists of indefinite composition of different gases and this composition can vary from place to place. Moreover, the different gases present in air show their individual properties which suggests that air is not a compound. 

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No, the percentage of water vapours in the air is not always same. The percentage of water vapour varies from time to time and from place to place. The amount of water vapour present in the air depends on a number of factors such as temperature and temperature changes from one place to another. This results in variable composition of water vapour in the air. 

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The given statement is false. This is because animals such as fishes use gills to obtain oxygen from the water. Moreover, some animals such as earthworms can even breathe through their skin. Thus, all animals do not breathe through lungs. 

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Yes, plants use oxygen during the day. This is because the plants require oxygen for performing respiration so that they can obtain energy. Like all living organisms, plants also require constant supply of energy and thus, they use oxygen during the day. 

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The solubility of air in water decreases with an increase in the temperature. 

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Air can be used to generate electricity through windmills. The winds generated from the air can be used to rotate the blades of the windmills. The rotation of these blades generates electricity through a dynamo. 

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Yes, the Earth would have been incredibly cold at the night and extremely hot during the day if the atmosphere was not present. The light and heat emitted by the Sun is absorbed by the atmosphere and some part of it is reflected back. This helps to keep the day temperature to an optimum value. During night, the heat trapped by the atmosphere helps the keep the temperature warm which prevents excessive lowering of temperature. Thus, in the absence of atmosphere, temperature of Earth will be very hot during the day and extremely cold during the night. 

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(d) water vapour
The presence of water vapour in air varies from place to place.

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(a) Oxygen is formed.
During combustion, oxygen is used, giving out carbon dioxide.

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(d) Atmosphere
Atmosphere is the layer of air surrounding the earth which contains oxygen.

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(b) Ozone
Ozone layer is a layer of gases present in the atmosphere that protects the Earth from the ultraviolet rays of the sun.

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(c) Oxygen used up in some natural processes is renewed by another natural process.
The percentage of oxygen in the air does not change because the oxygen used in respiration and combustion is replaced by the oxygen generated by plants during photosynthesis.

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(b) Nitrogen.
Though plants require nitrogen for their growth, plants cannot absorb nitrogen directly from the atmosphere.

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(c) Tape grass.
Stomata are absent in tape grass. Their body absorb the dissolved oxygen from water.

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(b) Carbon dioxide.
The percentage amount of carbon dioxide in air is the least, i.e., 0.03%.

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d. An industrial town

An industrial town is expected to have highest amount of pollution because of the presence of large number of industries. 

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The blanket of air surrounding the earth is called the atmosphere.

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The major component of air is nitrogen.

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Plants need the gas nitrogen, but they cannot take it directly from the atmosphere.

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Bodies of living things release energy during the process of respiration.

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False.
During respiration and combustion oxygen in the air is used up leaving behind carbon dioxide.

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Plants release the gas oxygen during the day and the gas carbon dioxide at night.

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False.
Like other living beings, plants also respire constantly irrespective of day and night. However, during day they also give out oxygen by photosynthesis than what they use for respiration.

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The percentage of carbon dioxide present in air is 0.03% by volume.

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Gills present in fish helps them to breathe in air dissolved in water.

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True. The changes in the weather occurs due to the atmosphere surrounding the earth.

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The oxygen cycle gets disturbed by deforestation.

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Atmosphere is a layer or blanket of air surrounding the earth. It extends up to 1000 kilometres above the earth's surface.

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Though carbon dioxide is present in lesser amount, it is very essential for both plants and animals. Plants require carbon dioxide to prepare their food. All animals in turn depend upon plants either directly or indirectly for their nutrition.

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The amount of water vapours present in the air is called as humidity.

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Fish have gills, with the help of which they breathe in the oxygen present in water. The water containing the dissolved oxygen passes through the gills and the oxygen gets absorbed by the gills.

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Yes, plants require nitrogen because it is involved in the growth of the plant.

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Ozone layer is a protective layer of gases which is present in the upper atmosphere. This layer blocks harmful ultraviolet rays from the sun and prevents them from reaching the earth.

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Air is said to be polluted when the composition of different gases in the air is dramatically altered. Moreover, addition of gases that are not normally found in the air also leads to air pollution. 

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Air is a combination of different gases. The major components of air are as follows:
(a) Nitrogen - 78%
(b) Oxygen - 21% 
(c) The remaining 1% consists of argon (about 0.9%), carbon dioxide (about 0.03%) and traces of other gases.
(d) It also consists of water vapour, dust and smoke which varies timely from place to place.

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If we breathe in through the mouth, the smoke and dust particles present in the air, enters directly into our respiratory system which is harmful and cause damage to our respiratory system. Hence, to avoid this, we must breathe through our nose, where these particles are filtered by the fine hairs and mucus present in nostrils.

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Stomata are the small openings present underneath the leaves of the plants with the help of which plants breathe in air. In water lilies, the leaves float on the surface of the water. In such condition, if the stomata are present underneath, it would be difficult for them to breathe in oxygen. Hence, in water plants stomata are present on the upper surface.

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Oxygen cycle is the movement of oxygen from the atmosphere to earth and vice versa. Plants and animals use oxygen present in the air for respiration. Oxygen is also used for combustion. This oxygen is replaced by the plants during photosynthesis. This cycle repeats balancing the volume of oxygen in the air.

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Following are the uses of air:
(i) It helps in restoring the water balance in nature.
(ii) It is used to generate electricity, with the help of wind mills.
(iii) It helps in seed dispersal for pollination.
(iv) It makes the flight of airplanes and helicopters possible.

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Sun emits heat and light, a part of which is absorbed by the atmosphere and the rest of it is reflected back. This prevents the earth from getting too hot during the day time. Similarly, during the night time, the trapped heat in the atmosphere prevents the earth from getting too cold. In this way the atmosphere help to maintain the right temperature on the earth.

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The steps that should be taken to reduce air pollution are as follows:
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1. We should try to use public transport instead of personal transportation.

2. More efficient fuels such as compressed natural gas (CNG) should be used because they produce less smoke.

3. We should try to plant trees so that the extent of air pollution is reduced. 

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Rusting of iron is a best example to show the presence of water vapour in the air. When the iron interacts with the air, the water vapour present in the air undergo chemical reaction with the iron forming a reddish brown substance on the surface of the iron which is called as rust.

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During the day time the leaves of the trees give off a plenty of oxygen in the process of photosynthesis. The amount of oxygen given off far exceeds the amount of carbon dioxide given out by the process of the tree respiring.
At night, there is no sunlight and photosynthesis stops. The trees however, continue to respire. As a result, trees give out carbon dioxide at night. Therefore, it is not advisable to sleep under a tree at night.

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This may be due to the damage of ozone layer in that particular region. The sun emits ultraviolet radiation which can cause skin cancer. The ozone layer, present in the upper atmosphere, acts as a shield and protects the earth from these rays. If the ozone layer is damaged, then a large amount of ultraviolet radiation falls on the earth and can cause skin cancer if people are exposed to the ultraviolet radiation.

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The gravitational force which attract every object towards the surface of the earth, also attracts the air, which makes the air denser on the surface of the earth. As the air moves up, i.e., away from the surface of the earth, the lesser gravitational force causes the air to be less dense or thinner. 

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Air heats up and cools down faster than water. Even when the air is cool, the water is relatively warm. Since, changes in water temperature are never as severe as changes in the temperature of air, aquatic animals such as fish are very sensitive to small changes in temperature.When a heater is put into the water, it was not as cold as the air to begin with. The increase in the warmth of the water coupled with the high temperature sensitivity of aquatic animals led to the death of the fishes in the aquarium.

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The correct decreasing order for the given burning candles for the time for which they will continue to burn is as follows:

Candle 4 - candle 2- candle 1- candle 3