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My name is Poon Cheng Moh. I have been teaching biology in SMK(P) Raja Zarina, Port Klang for 26 years. I sincerely hope that this blog on SPM Biology will be useful to both teachers and students.

Tuesday, November 9, 2010

To investigate the effect of the number of leaves on the rate of transpiration in a hibiscus plant.

Transpiration is the loss of water vapour from plants, especially in leaves. Transpiration occurs mostly through the stomata. The amount of water lost by a plant depends on its size, surrounding light intensity, temperature, humidity and wind speed.

Design an experiment to be conducted in the laboratory to investigate the effect of the number of leaves on the rate of transpiration in a hibiscus plant.

Objective

To investigate the effect of the number of leaves on the rate of transpiration in a hibiscus plant.

Problem statement

What is the relationship between the number of leaves and the rate of transpiration (in a hibiscus plant)?

Hypothesis

The more the number of leaves, the higher rate of transpiration.

Variables

Manipulated : Number of leaves / stomata

Responding : Distance travelled by air bubble (in ten minutes) // The rate of transpiration

Constant : Surrounding temperature / light intensity/ relative humidity/ type and size of plant used/ time

Apparatus and materials

Apparatus (A)

Potometer, beakers, knife, basin, stopwatch, ruler, capillary tube + rubber tubing, stoppered conical flask, beaker / basin, (sharp) knife, stopwatch, string

Materials (M)

Leafy shoot, vaseline, tissue paper / filter paper.

Technique

Measure and record the distance traveled by the air bubble in potometer in 10 minutes using a ruler// Calculate the rate of transpiration using the formula : Distance traveled by air bubble÷time (cm/min)

Procedure

1. Setup the apparatus as shown in diagram above.

2. Choose a hisbiscus shoot and cut the shoot end in water.

3. Insert cut stem in the potometer.

4. Adjust and mark the initial position of the air bubble.

5. Dry the surface of the leaves before the start of the experiment.

6. The light intensity / temperature/air movement/humidity of the surrounding must be maintained throughout the experiment.

7. Measure the distance traveled by the air bubble in 10 minutes.

8. By using the same plant, repeat the experiment by removing two leaves each time.

9. Use the same plant for all experiments.

10. Calculate the rate of transpiration.

Precaution

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.

Recording data/ result

Number of leaves

Distance traveled by air bubble in 10 min

(cm)

Rate of transpiration :

Distance traveled by air bubble/Time

(cm/min)

1st

2nd

3rd

Average




















Conclusion

Hypothesis is accepted. The more the number of leaves, the higher rate of transpiration.

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