How does the light intensity affect the rate of transpiration?
To investigate whether light intensity affects the rate of transpiration.
The higher the light intensity, the higher the rate of transpiration.
-Manipulated variable: Light intensity
-Responding variable : Time taken for the air bubble to travel 10 cm
-Fixed variable: air movement, temperature and relative humidity
2 Hibiscus plant of similar size, tissue paper, vaseline
Capillary tube (about 30 cm long), retort stand, 500 ml
beaker, basin, scalpel, rubber tubing (about 6 cm long), stop watch, ruler, thread
Measure and record the time taken for the air bubble to travel 10 cm using astopwatch and the rate of transpiration is calculated using the formula: Distance traveled by air bubble/time.
1. The leafy shoot is immersed in a basin containing water, and its stem is cut diagonally.
2. The leafy shoot is placed upright in the potometer’s capillary tube, through a stopper cork.
3. All equipment connection points are wiped with vaseline.
4. To trap an air bubble, the end of the capillary tube is removed from the basin, and then put back into the water.
5. A length of 10 cm is marked on the potometer.
6. The potometer is placed in the shade and using a stopwatch, record the time taken (in minutes) for the air bubble to move from point A to point B (10cm).
7. To reset the potometer, squeeze the rubber tubing so that the air bubble escapes into the beaker of water.
8. Repeat step 4 to 7 to get three readings with the same shoot in the shade and under strong sunlight respectively.
9. The average and the rate of transpiration measurement are recorded in the table.
1. The joint end of the stem and apparatus is smeared with vaseline to ensure no water
leakage and the apparatus is airtight.
2. The surface of the leaves must be dry before the start of the experiment.
Environmental condition of experiment
Time taken for air bubble to move from 10 cm (minutes)
Rate of transpiration
Shady (lower light intensity)
Strong sunlight (higher light intensity)
Hypothesis is accepted. The higher the light intensity, the higher the rate of transpiration.