Investigate the effects of immersing plant tissues in solutions of different water potentials, using the results to estimate the water potential of the tissues

To investigate the effect of immersing plant tissues in solutions of different water potentials, you can use plant tissues like potato or carrot. By immersing them in solutions of varying concentrations, you can observe changes in the tissue’s mass or length, which will indicate the movement of water into or out of the tissue. These results can then be used to estimate the water potential of the plant tissue.

Materials

• Potato or carrot cylinders or slices
• Sucrose solutions of different concentrations (e.g., 0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, 1.0 M)
• Beakers or test tubes
• Ruler (for measuring length) or balance (for measuring mass)
• Timer
• Tissue paper (for drying samples after immersion)

Method

1. Prepare Plant Tissue Samples: Cut the potato or carrot into uniform pieces (either cylindrical or rectangular) to ensure consistency. Measure and record the initial mass or length of each piece.
2. Prepare Sucrose Solutions: Make a series of sucrose solutions with varying concentrations, which will provide a range of water potentials.
3. Immerse Plant Tissue: Place each piece of plant tissue in a separate container with a different concentration of sucrose solution.
4. Allow for Osmosis: Leave the plant tissues in the solutions for a set period (e.g., 30 minutes to 1 hour).
5. Record Final Measurements: After the immersion period, remove the tissue samples, blot them gently with tissue paper to remove surface water, and measure their final mass or length.

Calculations and Analysis

1. Calculate Percentage Change in Mass or Length:
   • For Mass: text{Percentage change in mass} = frac{text{Final mass} - text{Initial mass}}{text{Initial mass}} times 100
   • For Length: text{Percentage change in length} = frac{text{Final length} - text{Initial length}}{text{Initial length}} times 100
2. Plot Results: Plot the percentage change in mass or length on the y-axis against the sucrose concentration (or water potential) on the x-axis.
3. Interpret Results:
   • A positive percentage change (increase in mass or length) suggests that water has moved into the tissue, indicating the tissue is in a solution with a higher water potential than its own.
   • A negative percentage change (decrease in mass or length) suggests that water has moved out of the tissue, indicating the tissue is in a solution with a lower water potential than its own.
   • The point at which there is no change in mass or length (0% change) indicates the water potential of the tissue, as there is no net movement of water.
4. Estimate Water Potential:
   • Using known water potentials of the sucrose solutions (which can be found in reference tables), identify the concentration where the percentage change is closest to zero. This concentration corresponds to the solution with a water potential approximately equal to the water potential of the plant tissue.

Explanation

The movement of water across cell membranes occurs via osmosis and depends on the relative water potential of the plant tissue and the surrounding solution:

• If the plant tissue has a higher water potential than the solution, water moves out, causing it to lose mass or length.
• If the plant tissue has a lower water potential than the solution, water moves in, causing it to gain mass or length.
• When there is no net movement of water, the water potential of the solution matches that of the tissue, providing an estimate of the tissue’s water potential.