This required practical covers Required Practical: Investigating Osmosis within Cell Transport for GCSE Biology. Diffusion, osmosis, active transport, factors affecting transport, surface area to volume ratio, and practical investigations It is section 7 of 19 in this topic. Revise both the method and the reason for each step, because practical questions often test understanding rather than pure recall.
🧪 Required Practical: Investigating Osmosis
Method - Effect of Salt Concentration on Potato Tissue
- Prepare specimens: Cut potato into identical chips (same size and shape)
- Initial measurement: Measure and record initial mass of each chip
- Set up solutions: Place chips in different salt concentrations:
- 0% (distilled water)
- 0.2%, 0.4%, 0.6%, 0.8%, 1.0% salt solutions
- Control variables: Same volume of solution, same temperature, same time period
- Leave for 24 hours
- Final measurement: Remove chips, pat dry carefully, re-weigh
- Calculate: Percentage change in mass = (Final mass - Initial mass) ÷ Initial mass × 100
Expected Results and Explanation
| Salt Concentration | Expected Result | Explanation |
|---|---|---|
| 0% (distilled water) | Mass increase | Hypotonic - water enters by osmosis |
| 0.2% - 0.4% | Small mass increase | Still hypotonic but less water movement |
| ~0.5% (isotonic point) | No change in mass | Same concentration as potato cells |
| 0.6% - 1.0% | Mass decrease | Hypertonic - water leaves by osmosis |
🎯 How to Improve Accuracy
- Use more potato chips for each concentration (larger sample size)
- Repeat the experiment multiple times to identify anomalies
- Control temperature throughout the experiment
- Use more intermediate concentrations for detailed results
- Pat chips dry more consistently to remove surface water
- Use the same variety of potato
- Measure mass to more decimal places
Practice questions for Cell Transport
Which statement best describes diffusion?
Explain how osmosis causes a plant cell to become plasmolysed when placed in a concentrated sugar solution.
Quick recall flashcards
Define osmosis
The movement of water molecules from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration) through a semi-permeable membrane.
Define diffusion
The movement of particles from an area of high concentration to an area of low concentration down a concentration gradient. No energy is required (passive process).