Using A Potometer To Estimate Tanspiration Rate

Question 1

What is a potometer and how does it work?

Answer 1

-a special piece of apparatus used to estimate transpiration rates
-it actually measures water uptake by a plant, but it’s assumed that water uptake by the plant is directly related to water loss by the leaves through transpiration

Question 2

Explain the process for working out transpiration rate using a potometer

Answer 2

1) cut a shoot underwater to prevent any air from entering the xylem. Cut it at a slant to increase its surface area available for water uptake
2) assemble the potometer in water and insert the shoot underwater so no air still can’t get in
3) remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water
4) check that the apparatus is watertight and airtight
5) dry the leaves and allow time for the shoot to acclimatise and then shut the tap
6) remove the end of the capillary tube from the beaker of water until one air bubble has formed, then put the end of the tube back into water
7) record the starting position of the air bubble
8) start a stopwatch and record the distance moved by the bubble per unit time. The rate of air bubble movement is an estimate of the transpiration rate

Question 3

What is the independent variable?

Answer 3

Temperature

Question 4

What variables must be kept constant?

Answer 4

-light
-humidity Etc