Osmosis Practical Experiment Lecture

Overview

• Focus: Effect of different solution concentrations on plant tissue (potato).
• Key Concept: Osmosis - movement of water into or out of plant cells.

Preparation of Potato Samples

• Tools & Materials: Cork board, ruler, top pan balance.
• Procedure:
  • Use cork board to cut uniform potato cylinders (same diameter for consistency).
  • Prepare three cylinders for testing with different solutions.
  • Remove potato skin (impermeable to water).
  • Cut cylinders to approximately 3 cm using a ruler (not highly accurate but acceptable for this experiment).
  • Measure lengths and masses using a ruler and top pan balance (accurate to hundredth of a gram).

Experiment Setup

1. Solution Types:
   • Distilled Water (pure water).
   • 0.25 Molar Sucrose (slightly sugary solution).
   • 0.5 Molar Sucrose (stronger sugary solution).
2. Procedure:
   • Measure 10 ml of each solution using a measuring cylinder.
   • Label each boiling tube to avoid confusion.
   • Optional: Use a bun to prevent evaporation if necessary based on temperature.

Experiment Execution

• Timing: Leave samples in solutions for 24 hours.
• Post-Experiment Measurements:
  • Distilled Water:
    • Increase in length (from 30 mm to 32 mm).
    • Increase in mass (from 2.92 g to 3.12 g).
  • 0.25 Molar Sucrose:
    • Length remains approximately the same (30 mm).
    • Slight increase in mass (from 2.96 g to 3.06 g).
  • 0.5 Molar Sucrose:
    • Length remains approximately the same (30 mm).
    • Decrease in mass (from 2.87 g to 2.62 g).

Data Analysis

• Calculate changes in length and mass for each sample:
  • Use final minus initial measurements.
  • Expect positive or negative values based on increase or decrease.
• Calculate percentage change for better comparison:
  • Formula: (Change in mass / Initial mass) * 100.
  • Helps adjust for initial mass discrepancies.*

Interpretation of Results

• Observations:
  • Potatoes in distilled water gain mass and length.
  • Potatoes in sugary solutions show varying degrees of mass change, indicating osmosis at work.
• Concentration Gradient Effect:
  • Higher sugar concentrations result in greater mass loss.
  • Line of best fit can be used to estimate internal sugar concentration of potato cells.

Conclusion

• The experiment demonstrates osmosis, where water moves in or out of plant cells due to concentration gradients.
• Understanding mass and length changes helps infer the concentration of solutes within the potato tissue.