Have you ever wondered if trees can transpire, that is, give off water? This tool will allow you to see and measure tree transpiration. This is done by measuring the amount of water a tree releases to the atmosphere over a period of time.

Engaging Questions

• What factors could have produced errors in the data for this activity?
• What could be done differently in order to reduce possible errors?

Teacher Goals

• You will collect observations on volume and mass of leaf transpiration.

Required Resources

• Materials:

  • Data Collection Sheet (this is attached to the first instruction)
  • pencil
  • plastic sandwich bags
  • twist-ties
  • balance
  • 10 ml graduated cylinder

Optional Resources

• Rate of Transpiration

  This web site provides some good background information.The material is from the The Greenhouse Project a ThinkQuest Program.

  • Rate of Transpiration
• What Tree is That? This the "Online Tree Guide" from The National Arbor Day Foundation. It is useful for learning how to identify types of trees.

  • What Tree is That?
• NRCS Plants Database This site is AWESOME!!! One can find any kind of plant with more facts than one should know. Most images are also free to use if cited correctly. It even spells out how to down load with citing methods. Great for identifying trees.

  • NRCS Plants Database

Steps

1. Gather Materials

   Obtain the materials listed in the Required Resources. Click on the link below to download and print the required data table.

   • Leaf Transpiration Table

2. Weigh Bag

   Weigh the plastic bag together with a twist-tie. Record the weight.

3. Tie

   

   For the selected tree, place the bag around several leaves. Make sure the bag is secure by tying it with a wire twisty. Record the number of leaves in the bag. Refer to the picture.

4. Collect Bags

   Check the bags. If the bag looks like there is enough water present to weigh, remove the bag carefully so as not to spill the contents. Retie the bag. (Make sure that all air is removed from the bag.)

5. Water Mass

   Weigh the bag with the water, then subtract the mass of the bag measured earlier to get just the mass of the water collected.

6. Water Volume

   Base on 1 gram of water equals 1 mL of water record the volume of water collected. NOTE: If only graduated cylinders are available, one may measure the volume of water collected and then determine the mass of the water.

7. Share Observations

   Use the attached form to share observations.

   • Leaf Transpiration Data Table

8. Conclusions

   Consider the engaging questions while writing your conclusions.

Teacher Notes

• Students may not be familiar with the process of transpiration, the release of water from the leaves of plants. This provides moisture and cooling to the atmosphere.The environmental conditions such as humidity, temperature, tree type, elevation, and amount of rainfall will cause the amount of water transpired to vary. If small amounts are collected, you may need to help in measuring. The bags should be left in place until you are ready to measure. It is important to leave the bags in place until measurable amounts are collected.The students must be familiar with tree identification. Use the Optional Resource if necessary.

• The following activities could be used as extensions that explores to more depth variables that may impact transpiration. 

  One may copy these lessons and modify as needed or create your own resources.

  • Do Trees Sweat More at Night or During the Day?
  • How does a leaf's surface area affects transpiration

Learner Notes

• Make sure the bags are tied on securely or some of the water may leak out. If the lab is carried out over a period of time, make sure that the same number of leaves is always used.