Theory:

Oxygen in water and soil
When water is heated for some time (before it starts boiling), we can see that small bubbles forms at the inner surface of the vessel.  The bubbles are seen as the air dissolved in water escapes. The water turns to vapour and begins to boil when heating continues.
 
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Aquatic animals inhale dissolved oxygen in water. When water is poured on a lump of soil, small air bubbles come out of the soil, indicating the presence of the air.
 
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Several plants and organisms that are living in the soil use oxygen to breathe. Various organisms like earthworms, rabbits, meerkats, and kangaroo mice form burrows and holes deep inside the soil.
 
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These holes makes the air to move in and out of the soil. During the raining season, when water fills up these spaces in the soil, animals and worms come out for respiration..
Replacing oxygen
Plants prepare their food with the help of oxygen in the process of photosynthesis. They produce oxygen more than they consume during this process. Through the process of photosynthesis, they helps to balance oxygen and carbon dioxide in the atmosphere. Here, we can see how both the plants and animals are interdependent on each other.
 
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Uses of air
1. The movement of air helps to rotate windmill. Windmills are used to generate electricity. It is also used to run mills and draw water from tube wells.
 
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2. It is used to sail yachts, gliders, aeroplanes, parachutes, etc.

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3. It helps birds, bats and insects to fly.

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4. It is also used in the dispersal of seeds and acts as a pollinating agent.
 
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5. Air plays a vital role in the water cycle process, which gives us rain.
 
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Reference:
https://cdn.pixabay.com/photo/2020/10/10/14/31/windmills-5643293_960_720.jpg
https://image.shutterstock.com/z/stock-photo-hot-water-in-pot-before-boiling-1701634666.jpg
https://image.shutterstock.com/z/stock-vector-illustration-of-rabbits-and-family-living-in-the-hollow-of-underground-house-cross-section-of-1080854894.jpg
https://image.shutterstock.com/z/stock-photo-earthworm-in-soil-closeup-shot-153200414.jpg
https://image.shutterstock.com/z/stock-photo-a-purple-parachute-in-a-blue-sky-on-a-sunny-day-28214938.jpg
https://image.shutterstock.com/z/stock-photo-an-american-bald-eagle-soaring-in-the-sky-1680397072.jpg
https://image.shutterstock.com/z/stock-photo-dandelion-clock-taraxacum-officinale-dispersing-seeds-against-a-green-blurred-natural-background-280171052.jpg
https://image.shutterstock.com/z/stock-vector-the-water-cycle-illustration-infographic-vector-1601995063.jpg
https://www.shutterstock.com/image-vector/process-tree-produce-oxygen-illustration-1114795847