Investigating Temperature & Wind Speed (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

Investigating the effect of environmental factors on the rate of transpiration from a leafy shoot

• Environmental factors can be investigated in the following ways:
  • Temperature: Temperature of room (cold room and warm room)
    • As temperature increases, the rate of transpiration also increases
  • Wind speed: Use an electric fan to mimic different wind speeds
    • As wind speed increases, the rate of transpiration also increases

Method

1. Cut a plant shoot underwater to prevent air from entering the xylem
2. Place shoot in the potometer apparatus
3. Set up the apparatus as shown in the diagram and make sure it is airtight, using Vaseline to seal any gaps
4. Dry the leaves of the shoot so that water does not block the stomata
5. Remove the capillary tube from the beaker of water to allow a single air bubble to form
6. Place the end of the tube back into the water
7. Set up the environmental factor you are investigating (temperature or wind speed)
8. Allow the plant to adapt to the new environment for 5 minutes
9. Record the starting location of the air bubble
10. Leave the potometer for a set period of time, e.g. 20 minutes
11. Record the end location of the air bubble
    • The further the bubble travels in the set time period, the faster transpiration is occurring
12. Reset the bubble by opening the tap below the reservoir
13. Change the wind speed or temperature (only one - whichever factor is being investigated)
14. Repeat the experiment

A potometer can be used to investigate the effect of temperature and wind speed on transpiration rate