Question 1 How will you show that air is present in a lump of soil?
Question 2 How will you show that air is dissolved in water?
Question 3 How do plants and animals maintain the balance of oxygen and carbon dioxide gases in air?
Question 4 State few uses of windmill?
Question 5 State uses of air?
Question 6 Why are burrows and holes dug deep into soil by the animals which live inside the soil?
Question 7 Why does a lump of cotton wool shrink in water?
Question 8 How do aquatic animals get oxygen required for breathing?
Question 9 Why earthworms come out of the soil only during heavy rains?
Also Read NCERT Solutions for Chapter 15 Air Around Us
Availability of oxygen to Animals and Plants Living in Soil
The animals which live in soil and the plant roots which grow in soil need oxygen to breathe. They get this oxygen from the air present in spaces between the soil particles.
Activity : Soil has air in it
We take some dry soil in a beaker. Add water to the beaker and stir the soil and water with a glass rod for a while. We will see the bubbles coming out of the soil. These bubbles are of the air which was present in spaces between the soil particles. Actually, when we stir the soil with water, then water enters the spaces between the soil particles and expels the air present there. This expelled air is seen in the form of bubbles coming out from the soil. So, this activity shows that soil contains air.
The animals which live inside the soil get oxygen for breathing (or respiration) from the air present between the soil particles. However, when it rains heavily, all the spaces occupied by air in the soil get filled with water and no air is left in the soil. In such a situation, the animals living inside the soil have to come out of the soil to obtain air for breathing (or respiration).
The earthworms normally live inside the soil. The earthworms come out of the soil only during heavy rains. During heavy rains all the spaces in soil which contained air get filled by rainwater leaving no air in the soil for the earthworms to breathe in. Due to this, the earthworms have to come out of the soil to obtain air for breathing (or respiration)
Many animals living in soil dig burrows and holes deep into the soil. These burrows and holes also make spaces available for the air to move into the soil so that it can be used to obtain oxygen by animals living there. The roots of plants which grow in soil get the oxygen for respiration from the air present between the soil particles.
A lump of cotton wool shrinks when put in water. This is because the lump of cotton wool contains a lot of air in the large spaces between its fibres which gets expelled by water resulting in its shrinkage.
Availability of oxygen to the Animals and Plants Living in Water
The animals (like fish) which live in water are called aquatic animals.
The plants which live in water are called aquatic plants.
The water of ponds, lakes, rivers and seas has some dissolved air in it. So, the animals and plants which live in water use the air dissolved in water for breathing (or respiration). The animals and plants which live in water use the oxygen dissolved in water for breathing (or respiration).
Activity: Water has air in it
Take water in a beaker and keep it on a tripod stand. Heat the water slowly by using a burner. Much before the water begins to boil tiny bubbles appear on the inside of the beaker. These bubbles are of the air which was dissolved in water. When water is heated, the solubility of air in it decreases due to which the air dissolved in water comes out of water in the form of tiny bubbles.
Water has some dissolved oxygen in it. The water animals (like fish) which live in water breathe in oxygen dissolved in water of pond, lake, river or sea. The plants that live in water also use the oxygen which is dissolved in water. Thus, there is oxygen in water too. If there were no oxygen in water, then no living things could survive in water.
How oxygen is replaced in Air
The oxygen of air being consumed by animals (and plants) in respiration, and in the burning of fuels is constantly being replaced by plants through the process of photosynthesis. In sunlight, plants use carbon dioxide and water to make food by the process of photosynthesis and produce oxygen gas. Plants also consume some of the oxygen for respiration but they produce much more oxygen than they consume.
Plants constantly refill the oxygen gas into air (or atmosphere) by the process of photosynthesis. The animals depend on plants for getting oxygen gas for breathing.
The carbon dioxide of air being consumed by plants in photosynthesis is constantly being put back into air by the respiration of animals (and plants), as well as by the burning of fuels by human beings.The animals and plants use oxygen from air for respiration and give out carbon dioxide gas. This carbon dioxide goes back into air. Similarly, the burning of fuels (wood, coal, kerosene, petrol, diesel and LPG) by the human beings uses oxygen from air and produces carbon dioxide gas. This carbon dioxide also goes back into air. Thus, the animals (including human beings) constantly put back carbon dioxide gas into air by the process of respiration and burning of fuels.
This carbon dioxide is then used by plants for making food by photosynthesis. Plants depend on animals for getting carbon dioxide gas for photosynthesis.
Respiration by animals and plants, and burning of fuels by human beings uses oxygen from air and puts carbon dioxide into air. Photosynthesis by plants uses carbon dioxide from air but puts back oxygen into air. The plants and animals help in maintaining the balance of oxygen and carbon dioxide gases in air (or atmosphere).
Uses of Air
Some of the important uses of air are :
(1) Air is used by human beings for breathing (or respiration): No human being (or other animal) can survive without the oxygen of air.
(2) Air is used for burning fuels (like wood, coal and kerosene, etc.) to make fire: This fire is used by man for cooking food and other heating purposes. No fuel can burn without the oxygen of air. Thus, air is necessary for burning fuels.
(3) Compressed air is used to fill tyres of various kinds of vehicles such as bicycles, scooters, cars, buses, trucks and aeroplanes. The air-filled tyres make the transport smooth and easier. The air is also used for inflating balloons and footballs.
(4) Air helps in the dispersal of seeds and pollen of flowers of several plants.
(5) Blowing air (called wind) is used to turn the blades of wind-mills: The wind-mills are then used to draw water by running pumps, to run flour mills and to generate electricity. The wind-mill used to run a pump to draw water from the ground. The blowing air (or wind) rotates the wind-mill blades continuously. When the blades rotate, the crank attached to the blades also rotates. When the crank rotates, then its U-bend lifts the pump rod up and down continuously. The rod works the pump which lifts the water from ground.
(6) Air helps in the movement of yachts (sailing boats), parachutes, gliders and aeroplanes.
(7) Air helps the birds, bats and insects in flying: The birds, bats and insects fly by pushing the air downwards and backwards with their wings.
(8) Air plays an important role in the water cycle in nature: This is because hot air, being lighter, rises up and carries the water vapour high up in the sky and helps in bringing rain. Moving air also carries rain clouds from one place to another and helps in bringing rain at all the places.
|Notes for Chapter 15 Air Around Us|