TRANSPIRATION : LIGHT INTENSITY

Design an experiment to investigate whether light intensity affects the rate of transpiration by using a simple photometer

Problem statement : How does the light intensity affect the rate of transpiration?

Objective : To investigate whether light intensity affects the rate of transpiration

Hypothesis : The rate of transpiration of plant is higher in strong sunlight

Variable

Manipulated variable : Light intensityResponding variable : Rate of movement of air bubble in the photometerFixed variable : air movement, temperature and relative humidity

Materials and apparatus:

Capillary tube (about 30 cm long), retord stand, 500 ml beaker, basin, scalpel, rubber tubing (about 6 cm long), tissue paper, vaseline, marker pen and stop watch, ruler , 2 Hibiscus plant of similar size

Technique : The movement of water in a given time is recorded using a stopwatch.

Procedure

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 phptpmeter’s capillary tube, through a stopper cork

3. All equipment connection points are wiped with vaseline4. To trap an air bubble, the end of the capillary tube is removed from the basin, and

then put back into the water5. A length of 5 cm is marked on the photometer6. The photometer 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 7. To reset the photometer, 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 respectively9. The average and the rate of transpiration measurement is recorded in the table.

Result:

Environmental condition of experiment

Time taken for air bubble to move from Point A to Point B (in minutes)

Rate of transpiration(cm/min)First

readingSecond reading

Third reading

Average

Shady (lower light intensity)

Strong sunlight (higher light intensity)

Conclusion: Hypothesis is accepted. In a shady condition, the plant’s rate of transpiration is lower

when compared with its rate of transpiration in strong sunlight

.