Introduction
Students will observe the process of transpiration in leaves.

Question

1. How much water will a leaf give off in a 24-hour period?

Materials
     Reclosable bag (quart size)
     Several small clean pebbles
     Tree in the sun
     Graduated cylinder

Procedures

1. Find an average-sized leaf on a tree which receives good sunlight.
2. Put the pebbles in the bag and close it around the leaf.
3. Wait 24 hours.
4. Carefully remove the bag and measure the volume and mass of the water collected inside.
5. Estimate the number of leaves on the tree and multiply by the volume of water collected. (Teachers should check with their own math program for an approved estimation procedure.)

Results

1. Volume of water = ________ ml.
2. Estimated number of leaves x volume of water collected = total water lost

             __________ x ____________ ml = _________ ml

Discussion Questions

1. How might transpiration of trees affect the temperatures and humidity in a forest?
2. Students can convert from the metric to the english system. (liters to gallons)
3. How much water does one tree give off in a year. (Average growing season in Illinois is 170 days; find out for your own area).
4. How much water is given off from the trees at your school, in one year?

Blowouts

1. Measure the temperature and humidity in a forest area. Compare with data gathered from a non-forested area.
2. What effect, if any, might trees have on weather and the atmosphere in a populated urban area? In an irrigated desert region?
3. What other implications are related to tree transpiration?

Conclusion

1. Students will note the large amount of water one tree gives off.