D2.3.4 Changes due to water movement in plant tissue Notes

Changes Due to Water Movement in Plant Tissue Bathed in Hypotonic and Hypertonic Solutions

1. When plant tissues are placed in different solutions, water flows in or out of their cells.
2. This causes dramatic changes in their texture and structure.

Hypotonic Solutions: Water Moves Into Cells

1. When plant tissue is placed in a hypotonic solution, water moves into the cells by osmosis.
2. This causes the cells to swell and become turgid.

Why Does This Happen?

1. The water potential of the hypotonic solution is higher than that of the cell's cytoplasm.
2. Water moves from the solution into the cell to equalize the water potential.

Effects on Plant Tissue

1. Increased Mass and Length: The tissue gains water, increasing its mass and sometimes its length.
2. Firmness: The cells become turgid, making the tissue firm and rigid.

Hypertonic Solutions: Water Moves Out of Cells

1. When plant tissue is placed in a hypertonic solution, water moves out of the cells by osmosis.
2. This causes the cells to shrink and become plasmolysed.

Why Does This Happen?

1. The water potential of the hypertonic solution is lower than that of the cell's cytoplasm.
2. Water moves from the cell into the solution to equalize the water potential.

Effects on Plant Tissue

1. Decreased Mass and Length: The tissue loses water, reducing its mass and sometimes its length.
2. Softness and Wilting: The cells become flaccid, making the tissue soft and limp.

Isotonic Solutions: No Net Water Movement

1. When plant tissue is placed in an isotonic solution, there is no net movement of water.
2. The tissue remains unchanged in mass and firmness.

Measuring Changes in Plant Tissue

1. To study osmosis, you can measure changes in the mass and length of plant tissue before and after placing it in different solutions.
2. Here's how:
   1. Prepare the Tissue: Cut uniform pieces of plant tissue (e.g., potato or carrot).
   2. Record Initial Measurements: Measure the initial mass and length of each piece.
   3. Immerse in Solutions: Place the tissue in solutions of varying concentrations (hypotonic, hypertonic, isotonic).
   4. Record Final Measurements: After a set time, remove the tissue, dry the surface, and measure the final mass and length.

Calculating Percentage Change

To compare results, calculate the percentage change in mass or length:

$$ \text{Percentage Change} = \frac{\text{Final Value} - \text{Initial Value}}{\text{Initial Value}} \times 100 $$

Deducing Isotonic Solute Concentration

1. The isotonic point is where there is no net change in the tissue's mass or length.
2. This indicates that the solute concentration of the solution is equal to that of the tissue.

How to Determine the Isotonic Point

1. Plot a Graph: Create a graph of percentage change in mass or length against solute concentration.
2. Find the Intersection: The point where the curve crosses the x-axis (zero change) represents the isotonic concentration.

Using Standard Deviation and Standard Error

1. To ensure reliability, repeat measurements and calculate statistical measures like standard deviation and standard error.

Why Use These Tools?

1. Standard Deviation: Measures the variability of data. A small standard deviation indicates consistent results.
2. Standard Error: Estimates how close the sample mean is to the true population mean. It is calculated as:

$$ \text{Standard Error} = \frac{\text{Standard Deviation}}{\sqrt{\text{Sample Size}}} $$

Practical Tips for Osmosis Experiments

1. Control Variables: Ensure all variables (e.g., temperature, size of tissue) are consistent except for the solute concentration.
2. Repeat Trials: Conduct multiple trials to improve reliability.
3. Use Accurate Tools: Measure mass with a balance and length with a ruler or caliper for precision.

Reflection

1. Understanding how water movement affects plant tissue is crucial for fields like agriculture and food preservation.
2. By mastering these concepts, you can predict and explain the behavior of cells in different environments.