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Water Cycle

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

The water cycle tracks the movement of water as it progresses through the states of matter and travels through the biosphere. Most of the water on earth is found in its oceans, but when the surface of a body of water gets warm it vaporizes, entering the air as gas and rising to form clouds. As more an more water enters the air it precipitates and falls to earth as rain or snow. Then it either returns to the oceans or falls to earth, sinking into the soil or flowing into rivers.

The water cycle is one of the basic cycles in Ecology, and it's a little bit different from some of the other cycles because unlike the others like say the carbon cycle you don't store a significant amount of water in the bodies of the various organisms in the planet because yes we do have water in our bodies but consider the oceans, who's bigger? They are so it can begin let's say in the ocean. How does water get from the ocean and lakes into the air? By evaporation, so it evaporates and as you know it starts to condense and forms the clouds and atmosphere community if you've been in the south. As the water starts to rise in concentration eventually it'll precipitate, precipitation is what scientists call rain hail snow pretty much water falls down from the sky that's precipitation. When it hits the ground it can be absorbed into the ground that's called infiltration and become part of the groundwater where it can stay for a while and eventually wind up back in the oceans or wind up back into the lakes and rivers.

You can also have what's called runoff that's when the water runs off to the ground and ultimately winds up in the oceans again or into the rivers and ultimately into a fresh water lake. Then you can also have it stored up temporarily in the form of ice or glaciers or snow. Now where organisms like ourselves do get involved in this and have a significant impact is through a process called transpiration. I've always had a problem remembering this and where I finally got it so that I can understand what transpiration was is I, this is a process where plants or trees release water through their leaves. This is something that they do to help pull additional water up from the roots. So I thought trees and transpiration, I thought I release water from my armpits I call that perspiration. So I combine those two into tree perspiration, transpiration. So transpiration of water from trees can actually put a fair amount of water into the atmosphere.

The trees themselves are not storing the water, they're simply acting as a funnel that help it evaporate faster and this is how rain forest can play a major part in the water cycle and influence the climate around them.