How Much Water Do Plants Lose to the Air?

Talk It Over

Plants use water to make food and stay alive, but they are not 100 percent efficient. They lose some water to the air through tiny holes in their leaves. How can we find out how much water plants lose?

Get

• 3 or more small potted plants,different kinds, in plastic pots
• Paper towels
• Kitchen scale or laboratory balance
• Water
• Clear plastic bags
• Plastic packing tape

Go

1. Water the plants until the soil is totally soaked and water runs out through the hole in the bottom of the pot.
2. Set the pots on a paper towel. Do not proceed until water stops running from the bottoms of the pots. Dry the outsides of the pots thoroughly.
3. Weigh the pots on the scale or balance. Record each weight.
4. Put a plastic bag over the top of each plant. Secure the bags to the pots with tape,like this:
5. Put the plant in a sunny spot for 1 hour or longer. Record the time and your observations
6. Carefully remove the bags from the pots and weigh each pot again. Calculate water lost from the plant this way:
7. Dry out the insides of the plastic bags with paper towels. Cover the plants again and reseal with tape. Return the plants to their sunny spot. Continue timing and weighing for several hours, perhaps several days, without adding any more water.

Stay Safe

Don't touch plant leaves if you have allergies. Wash your hands before and after handling the plants.

Go Easy

The "Go" procedure will work for you. Ask an adult to help you with the timing and weighing.

Go Far

You'll get better results with this experiment if you conduct several trials and average your results. Also, collect data for several individual plants of each type. For example, you might test 3 philodendrons, 3 English ivies, and 3 spider plants.

Do some research to learn more about transpiration. If possible, borrow a microscope from your school's science lab and find the tiny holes in leaves, called stomates, that let water and gases pass in and out of the plant. Design and carry out your own investigation on stomate action. You might try using a light coating of petroleum jelly on the undersides of leaves to block stomates, then using the "Go" procedure to measure water loss.

Show Your Results

Put the amount of water lost in a data table like this for "Go" and "Go Easy":

For "Go Far," modify the table to include each of the plants you test. Add a row for averages

For all the experiments, make bar or line graphs that show the water lost from your plants (on the vertical axis) as time goes on (the horizontal axis). Write a few sentences comparing water loss in your plants and draw some conclusions about which of your plants lost the most. Display your plants with your project. For "Go Far," you might also display a microscope and some slides of stomates.

Tips and Tricks

• Don't use terra cotta pots. They are porous and lose water through their surfaces. If you use plants in plastic pots, your only losses will be from the soil surface (which you can safely assume is the same for all the plants) and from the leaves.
• Small plants are easier to handle than large plants in this experiment. You'll find tiny houseplants in the gardening section of most discount stores and home improvement centers.

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CliffsNotes Parent's Crash Course Elementary School Science Fair Projects
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