Required Practical: Osmosis (AQA GCSE Biology)
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Biology Lead
Investigating Osmosis
- Aim: To investigate the range of concentrations of salt or sugar solutions on the mass of plant tissue
- You will:
- Prepare samples of potato and place them in different concentrations of sugar or sodium chloride (salt) solution
- Make measurements of mass and length of your samples before and after soaking them in solutions
- Calculate the percentage change in mass of plant tissue
- Plot, draw and interpret appropriate graphs
- In this practical, you should take care to prepare your samples of potato carefully and record your measurements accurately
- This practical can be carried out with either salt or sucrose solutions of at least five different concentrations
- The length of time that the potato cylinders are left will vary
- This experiment can be carried out in a water bath at 30℃ in 30 minutes
You will need to use apparatus appropriately to measure out the volumes of your solutions and record your measurements
- You should measure both the mass and the length of each potato cylinder before and after it has been submerged in solution - these measurements are your dependent variables from which you will calculate the percentage change in mass and length
- The independent variable is the concentration of salt or sucrose solution in mol dm3
- Important control variables are type and volume of solute in solution, temperature, and time
Osmosis Analysis
A positive percentage change in mass indicates that the potato has gained water by osmosis (net movement of water from the solution into the potato) meaning the solution is more dilute, a negative percentage change suggests the opposite
Exam Tip
This is an extremely common exam question – you should be able to calculate the percentage change in mass and length, and be able to plot a graph of the results.
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