Investigating osmosis in potatoes

In a nutshell

By putting potato cylinders into different concentrations of sucrose solution, you will be able to investigate osmosis in a real-life example. Depending on the water concentrations in the solutions, the potato cylinders will gain or lose mass, due to osmosis.

Equipment list

The following equipment list can be used to conduct an experiment to investigate osmosis in potato cylinders.

EQUIPMENT	USE
Potato	The plant tissue that will be used to investigate the effect of osmosis.
Five boiling tubes	To hold the potato cylinder and sucrose solution.
Test tube rack	To hold the boiling tubes.
Paper towels	To blot the potato cylinders dry.
A range of sucrose solutions with different concentrations	To investigate the effect of different concentrations of water solution on the potato cylinders.
Ruler	To measure the length of the potato cylinders.
Cork borer	To cut the potato cylinders, ensuring they have the same diameter.
Distilled water	To be added to a boiling tube and act a control for comparison.
$10\space cm^3$ measuring cylinder	To measure the correct volume of solution that will be added to the boiling tubes.
Labels	To label the boiling tubes with the concentrations of sucrose solution.
Scalpel	To trim the potato cylinders to ensure they are all the same length.
White tile	To put the potato cylinders on.
Top-pan balance (accurate to at least $0.01\space g$ )	To measure the mass of the potato cylinders.

Experiment 1: Investigating osmosis in potatoes

Experimental variables

All experiments have three different variables: the independent, dependent and control variables. The independent variable is the one you change. The dependent variable is the one which depends on what has been changed, therefore it is the one that is measured. The control variable is one which has been kept the same.

Independent variable	$The\ concentration\ of\ sucrose\ solution.$
Dependent variable	$The\ change\ in\ mass\ of\ the\ potato\ cylinders.$
Control variable	$The\ volume\ of\ sucrose\ solution\ used\ and\ the\ dimensions\ of\ the\ potato\ cylinders.$

Safety precautions

When carrying out experiments, it is very important to consider safety precautions. This is so you and others do not get hurt.

HAZARD	RISK	SAFETY MEASURE
Scalpel	The scalpel may cut your skin.	Be careful when picking up the scalpel and make sure to put it somewhere safe once you have finished using it.

Method

This is your instructions on how to complete the experiment.

Biology; Biology practicals; KS4 Year 10; Investigating osmosis in potatoes — 1. Least concentrated sucrose solution, 2. Most concentrated sucrose solution.

1.	Cut five potato cylinders using a cork borer. Trim off any potato skin and trim each cylinder to ensure they are all the same length using a scalpel and a ruler.
2.	Measure the initial mass each potato cylinder using the balance. Record these measurements in a table.
3.	Put $10\space cm^3$ of each concentration of sucrose solution into boiling tubes. Put $10\space cm^3$ of distilled water into the fifth boiling tube. Make sure to label each tube accordingly.
4.	Add one potato cylinder to each boiling tube and leave the cylinders inside for a chosen amount of time.
5.	Once the time is up, remove the cylinders and blot them try with the paper towels.
6.	Measure the final mass of each potato cylinder using the balance. Record the measurements for each concentration in the same table as before.

Analysis

This is how you can use your data to be able to form conclusions.

1.	Using your table, calculate the change in mass for each potato cylinder. $change\space in\space mass = final\space mass\space - initial\space mass$
2.	Then calculate the percentage change in mass and length for each potato cylinder. $percentage\space change\space in\space mass = {final\space mass\space -\space initial\space mass\over initial\space mass} \times 100$
3.	You should then plot the percentage change in mass and sucrose solution concentration onto a graph. The percentage change in mass should be on the $y$ -axis as it is based on the dependent variable. The sucrose solution concentration should be on the $x$ -axis because it is the independent variable. Draw a line through the points on the graph.

Conclusion

Your graph should show a negative correlation between sucrose solution concentration and percentage change in mass. As the sucrose concentration increases, the percentage change in mass increases. In the strongest sucrose concentration, the potato cylinder will have decreased its mass the most. This is because there is a greater concentration gradient between the potato cells which have a higher water potential, and the sucrose solution which has a lower water potential. As a result, a greater number of water molecules will move out of the potato cells by osmosis. This makes the potato cells flaccid and they will decrease their overall mass.

Biology; Biology practicals; KS4 Year 10; Investigating osmosis in potatoes

Evaluation

Once you have completed your experiment, it will be important to consider the quality of your data and how accurate your results are. Identify potential sources of random or systematic error and suggest possible improvements and further investigations.

Example

A limitation of this experiment could be that there are slight differences in the size of the potato cylinders. Therefore, for each sucrose concentration, the experiment should be repeated with several cylinders. By doing this, any anomalies can be identified and a mean value can be calculated. This will make the percentage change in mass more accurate.