Question

The figure below represents an experiment performed to demonstrate certain phenomena in plants. The setup was kept in sunlight for about two hours.

1. What is the aim of the experiment?
2. Define the process mentioned in (1) above.
3. What do you observe in the experiment as evidence of the process stated in (1) and (2) above?
4. Suggest a suitable control experiment for comparison.
5. Mention the precautions that should be taken for proper results in the experiment.

Answer 1

Experimental Setup:

1. A medium-sized plant with fresh leaves was taken.
2. It was completely covered with a polythene bag.
3. The polythene bag was then tied at the mouth to the bottom of the stem as shown in the figure.
4. The plant was then allowed to sit in the sun for 1-2 hours and then observed.

1. Aim of the experiment:

• The aim of this experiment is to show the process of transpiration through leaves.

2. Definition of the process:

• Transpiration is the physiological phenomenon in plants through which they lose water vapor through their stomata.
• When the atmosphere is particularly hot, the water loses as water vapor cools the plant, and water inside the stem and roots flows upwards or is 'drawn' into the leaves.

3. Observations of the experiment:

• It was observed that the polythene bag used to cover the plant has water droplets on its inner surface after a time period.
• It shows that water loss occurs during the transpiration process.

4. Control experiment for comparison:

• For comparison, in a control experiment, a measured amount of calcium chloride which is a water-absorbing material can be placed inside the polythene bag.
• Water loss from the leaves during transpiration can be evidenced by the increase in calcium chloride weight.

5. Precautions that should be taken during the experiment:

• The setup should not be placed in an extremely hot environment because then the water vapor inside the bag would not be able to condense.
• The polythene bag must be sealed tightly to avoid water vapor entry from the surroundings.