Practical Investigations on Osmosis

Introduction

• Topic: Practical investigations related to osmosis
• Previous Session: Discussed the theory of osmosis and relevant terminology
• Focus: Understanding an experiment often seen in exams involving osmosis and plant material

Experiment Overview

• Vegetable Used: Commonly carrot, parsnip, or potato; example uses potato
• Procedure Summary:
  • Cut vegetable into pieces of same length, preferably from the same potato.
  • Prepare solutions with different solute concentrations (sucrose).
  • Measure and record initial mass of potato pieces.
  • Place pieces in solutions for equal time periods.
  • Dry pieces to remove excess water after taking them out.
  • Measure and record final mass.

Control Variables and Solution Preparation

• Control Variables:
  • Length of potato pieces must be consistent
  • Use potato pieces from the same potato to ensure uniform solute concentration
• Solution Preparation:
  • Different concentrations using sucrose and water
  • Example: 150ml of pure water vs. 150ml of water with 40 grams of dissolved sugar

Procedure Details

1. Weighing Potato Pieces
   • Measure initial mass before placing in solutions (dependent variable)
2. Immersion in Solutions
   • Keep pieces in the solutions for the same length of time (e.g., 40 min)
3. Post-Immersion Handling
   • Dry pieces to remove excess water before measuring final mass
   • Record final mass after drying

Results Interpretation

• Mass Measurement:
  • Calculate change in mass (final mass - initial mass)
  • Example results: One potato piece increased in mass, another decreased
  • Record change in mass (grams)
• Percentage Change:
  • Formula: (Change/Original) x 100
  • Example calculation: 2.19% change
  • Important because it normalizes different starting masses of potato pieces

Observations

• Distilled Water: Potato gained weight
• Sugar Solution: Potato lost weight
• Explanation: Provided in a previous detailed video session

Possible Exam Questions

• Application of Results:
  • Determining water potential of potato cells using different sucrose concentrations
  • Plot mass change vs. sucrose concentration and find the zero-crossing point on x-axis (0.3 in example)
  • Refer to known water potential values based on this data point

Conclusion

• Takeaway: Understanding this experiment is crucial for exams on osmosis
• Next Steps: Review previous lessons for detailed theoretical explanations