Investigating Transpiration:

A potometer can used to estimate transpiration rate. It is a piece of apparatus that measures water uptake by a plant.

Cut a shoot underwater to prevent air from entering the xylem. Cut it at a slant to increase the surface area available for water uptake.
Assemble the potometer in water and insert the shoot underwater so no air can enter.
Remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water.
Check that the apparatus is watertight and airtight.
Dry the leaves, allow time for the shoot to acclimatise and then shut the tap.
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 the water.
Record the starting position of the air bubble.
Start a stopwatch and record the distance moved by the bubble per unit time. Calculating the speed of air bubble movement gives an estimate of the transpiration rate: distance moved/time taken.
Keep the conditions constant throughout the experiment e.g. temperature.

How can you see how environmental conditions affect transpiration rate?

You can use a potometer to estimate how different factors affect the transpiration rate. The set up is your control. You can vary an environmental condition, run the experiment again and compare the results to the control to see how the change affected the transpiration rate.

Light intensity - use a lamp to increase the intensity of the light that hits the plant. This should increase the transpiration rate. To decrease the light intensity, put the potometer in a cupboard which should decrease the transpiration rate.
Temperature - increase or decrease the temperature by putting the potometer in a room that’s warmer or colder than where you did the control experiment. An increase in temperature should increase the transpiration rate.
Air movement - use a fan to increase the air movement around the plant, this should increase the transpiration rate.

	Created by Chloe Wood about 5 years ago

GCSE Biology Note on B2 Revision , created by Chloe Wood on 18/03/2021.