AQA GCSE FOUNDATION Biology: Osmosis in Plant Tissues

AQA GCSE Foundation Biology: Osmosis in Plant Tissues

This tutorial will guide you through investigating osmosis in plant tissues. You will learn how to:

• Observe water movement through osmosis
• Calculate mass changes
• Analyze the direction of osmosis based on water potential

Experiment Setup

1. Prepare solutions of varying concentrations: You will need solutions of different sucrose concentrations (e.g., 0%, 5%, 10%, 15%). These solutions will represent different water potentials.
2. Select plant tissues: Use potato tubers or similar plant tissues that are easily cut into uniform shapes.
3. Cut the plant tissues: Cut the tissue into small, identical cylinders using a cork borer or a sharp knife.
4. Measure initial mass: Weigh each cylinder using a digital balance and record the mass in a table.
5. Place plant tissues in solutions: Place each cylinder into a separate beaker containing one of the prepared solutions. Make sure the cylinders are fully submerged in the solution.
6. Leave the plant tissues in the solutions: Allow the tissues to soak in the solutions for a predetermined time period (e.g., 30 minutes).
7. Remove plant tissues and pat dry: After the soaking time, gently remove the plant tissues from the solutions and pat them dry using a paper towel.
8. Measure final mass: Weigh each cylinder again and record the final mass in your table.

Calculating Mass Changes

1. Subtract initial mass from final mass: For each cylinder, calculate the mass change by subtracting the initial mass from the final mass.
2. Calculate percentage mass change: Divide the mass change by the initial mass and multiply by 100.

Formula:

Percentage Mass Change = [(Final Mass - Initial Mass) / Initial Mass] x 100

Analyzing Osmosis Direction

• Water potential: The water potential of a solution is the tendency of water to move from an area of high water potential to an area of low water potential. Pure water has the highest water potential.
• Hypotonic solution: A solution with a higher water potential than the plant tissue (e.g., 0% sucrose solution). Water will move into the plant tissue.
• Hypertonic solution: A solution with a lower water potential than the plant tissue (e.g., 15% sucrose solution). Water will move out of the plant tissue.
• Isotonic solution: A solution with the same water potential as the plant tissue. There will be no net movement of water.

Results and Discussion

1. Record your data: Create a table showing the initial mass, final mass, mass change, and percentage mass change for each cylinder in each solution.
2. Plot a graph: Plot a graph with percentage mass change on the y-axis and sucrose concentration on the x-axis.
3. Analyze the graph: Observe the trend in the graph.
   • Hypotonic solutions: You should see a positive percentage mass change (gain of water).
   • Hypertonic solutions: You should see a negative percentage mass change (loss of water).
   • Isotonic solution: There should be little to no change in mass.
4. Explain your findings: Use your knowledge of water potential and osmosis to explain the observed changes in mass.

Conclusion

This experiment demonstrates the principle of osmosis and how it affects the movement of water in plant tissues. By understanding osmosis, you can explain how plants take up water and maintain their turgidity, which is essential for their growth and survival.