Water Cycle

The chemical formula for water is H₂O. On earth, water can be found as a liquid or a solid. In the atmosphere, water is in a gas form called vapor.

Check out the diagram below. It is a representation of all the events in the water cycle. You might want to copy and paste it into a Notes Page and record information about the parts and their relationship to each other in the cycle.

As you can see in the diagram:

water comes to the earth in some form of precipitation (rain, snow or hail.)
at some point, water is heated by the sun and turns back into a gas called water vapor. This is process is called evaporation.
the water vapor rises into the atmosphere, eventually cooling, forming clouds; this part of the cycle is called condensation.
eventually the cycle starts over and it precipitates again.

In an ecosystem, the living organisms also take part in the water cycle.

Plants take in water through their roots and return water vapor to the air in a process called transpiration.
Animals drink water or get it in food they eat and then as their bodies convert the food to energy, they release water vapor into the air as a waste product of a process called cellular respiration.
Water is also excreted as urine.
After an organism dies and decomposes, water is recycled right back into the environment.

So you see, animals and plants have a part to play, even in the water cycle.

Okay, now go back to your freezer and get the glass.

Hold the glass near your mouth and exhale/breathe on it several times.

What happened to the glass? Did frost form on it?

The frost is water vapor from your body recycling back to the biosphere through respiration.

What happens when you fill up that nice cold glass with your favorite soda and drink it? Sooner or later you are going to need to take a trip to the bathroom…that’s excretion.

The Environmental Protection Agency (EPA) has a great water cycle interactivity. Here’s your chance to play around a bit and really learn the water cycle.

EPA Water Cycle

Close This Window