THE WATER CYCLE AND OXYGEN CYCLE

THE WATER CYCLE AND OXYGEN CYCLE

The Water Cycle

As the sun shines on both the land and the seas, the land is heated up faster than the seas. Hot air rises over the land. This creates difference in air pressure between the land and the seas. A sea breeze results, blowing from the sea to the land, and carries a lot of water vapour with it.

As moisture containing air rises on land it cools, clouds form and condensation into water drops occurs. Other sources of water vapour which enter the clouds include:

1.  Water loss from the land by evaporation.

2.  Water loss by plants through transpiration and excretion.

The water drops formed by condensation of water vapour in the upper part of the atmosphere fall as rain. As rain falls, a part of it soaks into the ground and infiltrates downwards to the water table. Some of it is called runoff water, flows along the surface of the ground into streams, rivers and lakes. The water in the streams, rivers and soil eventually flows into the sea (ocean). The event described above takes place all the time and constitutes the water cycle.

Water Cycle Diagram

 

The Oxygen Cycle

All living things need oxygen for respiration. Oxygen and food are converted into energy and carbon (iv) oxide. Green plants change the carbon (iv) oxide back into oxygen. Respiration and combustion use up oxygen and make carbon dioxide, photosynthesis uses up the carbon dioxide and makes oxygen again.

Oxygen Cycle Diagram