Class X Practical: Plant Life - Transpiration

Objective

To demonstrate the process of transpiration in plants and measure its rate.

Guidelines

1. Bell Jar Demonstration

1. Setup: Take a well-watered potted plant and cover the pot and soil surface with a plastic sheet to prevent evaporation from the soil.
2. Enclosure: Place the potted plant under a bell jar. Seal the base of the bell jar to the ground or a glass plate to create an airtight enclosure.
3. Observation: Place the setup in sunlight. Observe the inner surface of the bell jar after a few hours.
4. Expected Outcome: Droplets of water will appear on the inner surface of the bell jar, demonstrating that plants release water vapor into the atmosphere through transpiration.

2. Cobalt Chloride Paper Test for Unequal Transpiration

1. Preparation: Obtain dry cobalt chloride paper (blue in color).
2. Application: Attach a piece of dry cobalt chloride paper to the upper surface and another piece to the lower surface of a healthy leaf using clips or adhesive tape.
3. Observation: Observe the color change of the cobalt chloride paper on both surfaces over time.
4. Expected Outcome: The cobalt chloride paper on the lower surface of the leaf will turn pink faster and more intensely than that on the upper surface, indicating a higher rate of transpiration from the lower epidermis due to the presence of more stomata.

3. Ganong’s Potometer – Measure Uptake of Water

1. Setup: Assemble the Ganong's potometer. Ensure it is completely filled with water and free of air bubbles. Insert a freshly cut, healthy twig into the apparatus, ensuring an airtight seal.
2. Initial Reading: Adjust the air bubble in the capillary tube to the starting point and note the initial reading.
3. Observation: Place the potometer in different environmental conditions (e.g., light, fan, dark) and observe the movement of the air bubble along the capillary tube over a set period.
4. Calculation: Calculate the rate of water uptake (and thus transpiration) by measuring the distance moved by the air bubble and the cross-sectional area of the capillary tube.
5. Expected Outcome: The air bubble will move, indicating water uptake by the twig to compensate for water lost through transpiration. The rate of movement will vary with environmental factors.