Investigating Transpiration.

Question 1

How do you set up a potometer?

Answer 1

1. Cut a shoot underwater at a slant to prevent air from entering the xylem.
2. Assemble a potometer with a capillary tube end submerged in a belaer of water.
3. Insert the shoot underwater.
4. Ensure the potometer is air and watertight.
5. Dry the leaves and allow the leaves time to acclimate.
6. Shut the tap reservoir.
7. Form and air bubble by quickly removing the end of the capillary tube and quickly putting it back.
8. Record the initial position of the bubble.
9. Record the distance moved in a certain amount of time.
10. Calculate the volume of water uptake in a given time: Use the radius of the potometer to calculate the are of the cross-section and multiply it by the distance the air bubble travelled.
11. Calculate the rate of water uptake: the volume of water uptaken/ time.
12. Change in variable such as temperature, light intensity, wind intensity and humidity.

Question 2

Suggest the limitations to the potometer method?

Answer 2

1. The amount of water uptake by the xylem does not always equal the rate of transpiration as some of the water is used for photosynthesis and support.
2. The rate of movement in the potomete may not be the same are the rate of movement in the shoot. This is because the shoot potometer does not have any roots and the xylem are very narrow.