Science Buddies: "Ask an Expert"

I'm trying to help my son with a project. Does anyone know why do leaves give off water.

startreace,

The main product that leaves produce is oxygen, which is a by-product of the process of photosynthesis. Plants use photosynthesis to create the sugar that they need as food. Here is an article that goes in-depth about the subject of photosynthesis: http://en.wikipedia.org/wiki/Photosynthesis

Or are you asking why the leaves do not soak up all of the water that falls on them?

If you could be more specific, that would help.

Hi Startreace

The phenomenon you are describing is called transpiration.
See http://ww2010.atmos.uiuc.edu/(Gh)/guide ... /trsp.rxml
and
http://en.wikipedia.org/wiki/Transpiration

I believe it is generally considered a side effect of the plant having the stoma (leaf pores) open to let in carbon dioxide.

There are some experiments you can do to demonstrate how this occurs at different rates when the plant has its stoma open compared to under conditions when it may shut its stoma.

Best of luck,
Caroline