How does a leaf's surface area affects transpiration

Engaging Questions

• How do the transpiration rates compare among the different surface areas?
• Can you describe several adaptations that enable plants to reduce water loss?
• Since the surface area for your leaf stayed the same, why did the volume vary?

Teacher Goals

• By using the scientific method, you will determine how surface area affects the rate of transpiration of tree leaves.

Learner Goals

• Priority Academic Student Skills - 12.2.1.1 Process Standard 1. Observe and Measure - Observing is the first action taken by the learner to acquire new information about an organism or event. Opportunities for observation are developed through the use of a variety of scientific tools. Measurement allows observations to be quantified. The student will accomplish these objectives to meet this process standard.
• Priority Academic Student Skills - 12.2.1.3 Process Standard 3: Experiment - Experimenting is a method of discovering information. It requires making observations and measurements to test ideas. The student will accomplish these objectives to meet this process standard.
• Priority Academic Student Skills - 12.2.1.4 Process Standard 4: Interpret and Communicate - Interpreting is the process of recognizing patterns in collected data by making inferences, predictions, or conclusions. Communicating is the process of describing, recording, and reporting experimental procedures and results to others. Communication may be oral, written, or mathematical and includes organizing ideas, using appropriate vocabulary, graphs, other visual representations, and mathematical equations. The student will accomplish these objectives to meet this process standard.

Required Resources

• Data collection sheet, pencil, plastic sandwich bags, twist-ties, balance, 10 ml graduated cylinder, thermometer, GPS, and graph paper

Steps

1. Transpiration Tool (not done)

   Refer to the attached tool Transpiration: Trees Have Water? for instructions to set up the water collection system. Each lab group should set up their system for the same time period.

2. Surface Area

   After the lab has run for the chosen length of time, pick the leaves that were used in the experiment. Place the leaves on 1 cm interval graph paper and draw an outline of the leaves.

3. Calculate

   Look at the graph paper and calculate the surface area by counting the number of centimeter squares that were covered.

4. Data Table

   Obtain and record data from all students. Calculate the average for each tree type.

5. Convert

   Depending on the length of time for transportation to occur, the ml of water may be small. If this is the case, change the cm squared to meter squared by dividing by 10,000. Ex. 22 cm squared = .0022 m squared.

6. Water loss/ surface area

   To calculate the water loss/ surface area, take the ml collected and divide by the surface area. Ex. 0.04 ml / 22 cm squared = 0.18 ml/cm squared Ex. 0.04 ml / 0.0022 m squared = 18.2 ml/m squared

7. Graph

   Graph the following information: Tree type and suface area versus volume of water collected.

8. Conclusions

   Write a conclusion based on your observations and your classmates' results. Type in your data on the data form.

9. Engaging Questions

   Incorporate your answers to the "Engaging Questions" (found in the Teacher's Guide of this lesson) in your conclusions.

Teacher Notes

• Setup time - 20 minutes. Follow up measurements - 20 minutes
• 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.

Learner Notes

• Make sure to pull the branch downward when you remove the bag so as not to lose any water.

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