3.3.8 Practical: Investigating the Rate of Transpiration

Question 1

What can be used to investigate the effect of environmental factors on the rate of transpiration?

Answer 1

A potometer

Question 1

Describe a method to investigate the rate of transpiration.

Answer 1

Cut a shoot underwater
This is done to prevent air from entering the xylem
Place the shoot in the tube
Set up the apparatus as shown in the diagram
Make sure it is airtight, using vaseline to seal any gaps
If air enters the apparatus the readings will be affected
Dry the leaves of the shoot
Any moisture present on the leaves will affect the rate of transpiration
Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water
Set up the environmental factor you are investigating
Allow the plant to adapt to the new environment for 5 minutes
Record the starting location of the air bubble
Leave for a set period of time
Record the end location of the air bubble
Change the light intensity or wind speed or level of humidity or temperature (only one - whichever factor is being investigated)
Reset the bubble by opening the tap below the reservoir
Repeat the experiment
The further the bubble travels in the same time period, the faster transpiration is occurring and vice versa

Question 2

How can airflow be investigated?

Answer 2

Set up a fan or hairdryer

Question 3

How can humidity be investigated?

Answer 3

Spray water in a plastic bag and wrap around the plant

Question 4

How can light intensity be investigated?

Answer 4

Change the distance of a light source from the plant

Question 5

How can temperature be investigated?

Answer 5

Temperature of room (cold room or warm room)