Check Out Plant Transpiration!

This lesson developed by Reach Out! Recommended Age: Later Elementary and Middle School


Do green plants give off water from their leaves? Can I conduct an experiment to see evidence of transpiration?

What you need:

What to do:

  1. Use your ruler and pencil to measure and mark a rectangle from the cardboard shirt box that is four by six inches. Cut out the rectangle.
  2. With the sharp tip of the pencil, poke a little hole in the middle of the cardboard rectangle.
  3. Break off a healthy leaf and stem from the geranium plant.
  4. The leaf stem is called a petiole. Put the petiole of the leaf in the hole in the cardboard rectangle.
  5. Fill one of the glasses three-quarters full with water.
  6. Cut the cardboard on top of the glass with the water in it so the stem is down into the water and the leaf is on top of the cardboard- not in the water.
  7. Take a little bit of vaseline and put it around the hole. This is to keep evaporated water from the glass seeping up into the top glass.
  8. Put the second glass upside down over the leaf, resting against the other glass' mouth.
  9. Put the glasses on a ledge or table top near a window where there is a good source of sunlight.

What is happening?

Watch what happens after 3 or 4 hours. Do you see little drops of water on the inside of the top glass? Where is the water coming from? If you plugged the hole around the stem, the water from the bottom glass shouldn't be getting up into the top gla ss.

What is happening is called "transpiration." This is the process whereby the leaves on green plants give off water that they do not need. Look at the bottom of the geranimum's leaves. You will see little dots which are called stomates. The stomates give off the excess water the plant doesn't need.

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