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The Effect of Air Movement on Transpiration in Plants

Scientists: Dr. Sydney J. Quintana, Dr. James W. Maddux, Dr, Ashlynn S. Albert

Expected Results

  • Controlled average rate of water uptake 0.85cm/minute.
  • When wind was added at 0.98m/s, transpiration rate increased to 1.1cm/minute, (increased 23%).

Methods

1. the potometer is immersed in water to remove air bubles

2. the screw clip is opened to fill the capillary tube with water

3. the branch of the plant was cut while in water

4. the cut end of the branch was pushed through the hole of the rubber stopper in the water

5.place a beaker full of water under the end of the capillary tube

Materials

Cont.

11. Record the time it was taken for the air bubbles to move from points P to Q

12. The air bubbles were reset at point P by reopening the screw clip

13. Steps 11 & 12 were repeated twice and the mean time was calculated

14. Steps 11-13 were repeated by placing the potometer under a fan of different speeds

The rate of transpiration was calculated using the following formula

Rate of transpiration = P10/t cm/minute

T= time taken for air bubbles to move from P to Q

6. Close the screw clip and remove the potometer from water

7. Wipe the leaves and the stem with tissue paper

8. Put the Vaseline across the joints to ensure that there is no air seeping through

9. Leave the potometer aside until all the air bubbles in the capillary tubes move at a steady pace

10.Put the ruler between point P and point Q along the capillary tube marked 10 cm apart

  • Potometer
  • Stopwatch
  • Ruler
  • Knife
  • Rubber stopper with holes
  • Tissue Paper
  • Fan
  • Plant (any one of your choosing)
  • Vaseline
  • Water

Air Movement (Wind)

  • Boundary Layer
  • thin layer of still air that hugs the surface of the leaf (humid air)
  • in transpiration, water vapor leaving stomata must diffuse through this layer to reach the atmosphere of moving air
  • larger boundary layer = decrease in transpiration
  • Increasing air movement will make the boundary layer smaller which will increase transpiration

Background Information

  • Transpiration is the process of losing water in plants.
  • Cohesion-tension theory
  • Concentration gradient
  • Tension in the vessels pulls the water upwards towards the leaves.
  • Molecular forces of cohesion, and adhesion play a role
  • Light causes potassium ions to be pumped into the guard cells - increases solute concentration - water diffuses into the cells - stomata opens

Potometer

What is it? Why is it important? Why do we need it?

-An instrument for measuring the amount of water that a plant loses through transpiration, consisting of a sealed vessel of water with a cut inserted so that moisture can escape only through absorption and transpiration

-The function of the cut is to allow an air bubble to travel back to the start of the measuring scale when the experiment is repeated. As water moves up through the plant the air bubble moves along the scale giving a measure of water absorbed by the plant over time and hence the transpiration rate.

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