Required Practical - Osmosis in Plant Tissue
Biology: AQA GCSE Higher, topic 1.3.9
Concentrations of Salt or Sugar Solutions on Plant Tissue
The aim of this practical is to investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue using osmosis theory.
Calculate the results
- Using the recorded results, calculate the change in mass and percentage change.
- To find the percentage change in mass =
Plot the results
- Plot a graph of percentage change in mass (y-axis) against concentration of solution (x-axis).
- The point where the curve crosses 0% indicates the isotonic concentration of the potato cells.
Variables
- Independent variable:
- Concentration of salt or sugar solution (mol dm-3)
- Dependent variable:
- Change in mass (and length) of potato cylinders
- Control variables:
- Type of plant tissue, temperature, volume of solution, time left in solution, size and shape of potato pieces
Explanation
- In pure water (0.0M), potato gains mass → water moves into the cells by osmosis.
- In strong solutions (1.0M), potato loses mass → water moves out of the cells.
- The concentration where no change occurs is isotonic – equal concentration inside and outside the cells.
Evaluation and Improvements
- Possible errors:
- Unequal potato size or surface area
- Inaccurate drying before weighing
- Evaporation of the solution
- Improvements:
- Use more concentration points for accuracy
- Repeat each concentration at least 3 times and calculate a mean
- Use a more precise balance
Test yourself on Required Practical - Osmosis in Plant Tissue
Why should potato cylinders be dried gently before reweighing?
What are some possible sources of error in the experiment?