# 1.3.5 Required Practical: Osmosis

### 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.

### Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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