Effect of Humidity on Rate of Transpiration

1. Effect of Humidity on Rate of Transpiration Samantha Guhan Lucy Hu Savannah Jensen Axel Ramos KartikSawant

2. Why Should We Care??? • Plants need to cool themselves for several reasons • When temperatures are too high, energy systems slow, and growth and flowering stop • Plants are very important to our environment due to their source of food and their role in controlling the surrounding environment. • Humidity varies from place to place • Finding the optimal humidity gives insight for optimal growth of plants with high water needs

3. Variable • Independent: Number of of sprays of water (humidity level) • Dependent: Barometric pressure (in mm Hg) • Control Variables: See next slide

4. Controls

5. Methods and Materials • Materials PASPORT Xporter GLX • PASPORT Barometer Pressure • Senor • PASPORT Extention Cable • Large Tub Full of Water • Utility Clamp • Three Finger Clamp • Plastic Tubing Clamp • Plastic Tubing • Razor Blade • 95 W light source • Metric ruler • Plastic galleon bag • Mister bottle • 5 mL plastic syringe • Plant cutting

6. Procedure • Obtain a plant cutting from the plant blush near the Chemistry lab • Take a plant cutting and submerge in the tube of water- cut the stem from a 45 degree angle. Keep newly submerged end in water. • Prepare plastic tubing by filling with water and connect plant to tubing by inserting the cut plant stem into tubing

7. Equipment Image Assemble the equipment as seen here

8. Procedure • Set up a 100 W light source 30 cm from plant cutting • Allow 5 minutes to adjust to the environment • USE GLX to measure Barometric pressure • Once 5 minutes have passed begin recording pressure of 10 minutes

9. Creating Differing Levels of Humidity • Level 1 Control: no sprays • Level 2: 5 sprays • Level 3: 10 sprays • Level 4: 15 sprays • Level 5: 20 sprays

10. Results

11. Results

12. Biological Explanation • The rate to transpiration decreased as the humidity level increased • Why did this happen??? • Biologically, bulk flow in plants is a result of pressure differences. In this case, the xylem flow is due to transpiration-cohesion-tension (aka transpiration). This is ultimately the result of a pressure gradient through the plant. As the pressure gradient “pulls” the water molecules up, those water molecules will pull on a chain of water molecules, bonded together through hydrogen bonds. They bond to each other (cohesion) and the walls of the xylem (adhesion) ultimately being pulled up in a string.

13. Biological Explanation Cont. • Due to the face that xylem is mainly movement of water (though it also does transport some minerals), xylem deals with water potential (), which is the “physical property predicting the direction in which water will flow.” Water will flow from areas of high water potential to areas of low water potential. The surrounding air has a very low water potential, while, in comparison, the water potential is higher in the stem and leaf of the plant. Campbell, Neil A., and Jane B. Reece. Biology. 7th ed. San Francisco: Pearson, Benjamin Cummings, 2005.

14. Why do we care??? • It affects agricultural locations of crops and the amount of watering that a plant needs • Sources of Error • Stalks of plants and different sizes and numbers of leaves • Time spent equalizing was not controlled • Light bulb was broken in the middle of the experiments. Trial 2 went without light for a couple of minutes, during the level with 10 sprays.

15. Future Work • Test the effect of the following on the rate of transpiration • Different types of plants • Different levels of wind • More levels of humidity • Different temperatures