2.58B - Practical: Factors affecting transpiration

Edexcel IGCSE Biology

what apparatus do you use?

a potometer

what are the two types of potometer?

• mass potometer

• bubble potometer

how does a mass potometer work?

measures a change in mass of a plant to measure how much water has evaporated from the leaves and stem

how does a bubble potometer work?

measure the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation

shown by the air bubble moving as the plant pulls water up through the stem to replace water lost by evaporation

explain how to investigate the effect of light intensity on transpiration (bubble potometer)

1. cut shoot underwater to prevent air entering xylem
2. make sure apparatus is airtight
3. dry the leaves of the shoot (wet leaves will effect the results)
4. remove the capillary tube from the beaker of water to allow a single air bubble to form and place tube back in water
5. set up lamp 10cm away from leaf
6. record starting location of bubble
7. record end location of bubble after 30 minutes
8. change light intensity
9. reset bubble using resevoir tap
10. repeat experiment

what calculation do you use to calculate rate of transpiration?

how do you investigate other factors?

• airflow: fan/hairdryer

• humidity: spray water in plastic bag and wrap around plant

• temperature: temperature of room