Water is essential for all the life processes. About 80% of water is present in a living cell. It covers about 73% of surface of the earth in the form of lakes, rivers, oceans. There is a continuous cycling of water between biotic and abiotic components of ecosystem and the atmosphere. This cycling takes place through precipitation and evaporation.



  1. Formation of clouds: Water evaporates from oceans and rivers.Transpiration form plants also produced vapours. These vapours are carried by wind. On cooling water vapours condense to form clouds.
  1. Precipitation: The winds colloids with mountains and return back. Now the height of these wind drops. They are unable carry water vapours. There water falls on the earth surface in the form of precipitation (rain, snow, hail etc.)
  2. Formation of glaciers: Some snow permanently deposits on high mountains. It forms glaciers. Glaciers are natural reserves of clean water. They are the main source of water for rivers. Irrigation system depends on these glaciers.
  3. Flow of water in ponds, lakes and rivers: Some water again evaporates into the atmosphere. Some infiltrates into the soil and joins the water table. The remaining water moves as runoff and seepage in to ponds, lakes. rivers. It ultimately moves into the oceans. Water keeps on evaporating in the atmosphere and form clouds
  4. Water in plants: Water from the soil is absorbed by plants. Plants special roots hairs for absorption of water. Some of water is used during photosynthesis. Most of water returns into the atmosphere through evapotranspiration.
  5. Water in animals: Animals also take water directly or indirectly through the plant foods. This water is then return into the atmosphere through excretion and evaporation.

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