Date:
Topic: Osmosis
Time: 1 hr
IB Biology
The effect of osmosis on potato tissue
Aim
To assess the effect of different concentrations of salt (NaCl) solution on osmosis in the cells of the
potato tuber
To estimate the osomolarity of potato by bathing them in hypotonic and hypertonic solutions.
Research question: To what extent does increasing the solute concentration NaCl (0, 1, 2, 3,4, 5%)
cause a change in the osmotic movement of water in potato cells
Hypothesis
The change in mass of the potato tuber cells will be inversely proportional to the concentration of salt
solution in which they are placed. This is because low concentrations of salt solution will have a higher
water concentration than the solution inside the potato cell causing the diffusion of water into the cells
and an increase in mass. High concentrations of salt solution will have a lower water concentration
than the solution inside the cells causing the diffusion of water out of the cells and a decrease in mass
(Allott & Mindorff, 2014).
Selection of variables
Independent variable
Dependent variable
Control variables
Concentration of salt
(NaCl) solution (0%,
1%, 2%, 3%, 4%, 5%)
% change in mass of 1. Volume of salt solution
2. Temperature of salt solution
cylinders of potato
3. Type of potato
tuber cell
4. Diameter and length of potato tuber cylinders
5. Time potato is submerged in the salt solution
6. Apparatus to measure volume and mass
Method for controlling variables
1. Use a 100ml (±1ml) measuring cylinder to measure 50ml of each solution of salt
2. Use a thermometer to monitor the room temperature to check that does not vary
3. Use the same potato tuber to cut all cylinders of potato tuber cells
4. Use a “core borer” and ruler to cut cylinders of the same diameter with a length of 30.0mm
(±0.5mm). Increase the surface area to speed up osmosis by cutting the 30.0mm cylinders into 6 x
5.00mm cylinders (approx.)
5. Place the cylinders of potato tuber cells in the salt solutions at the same time and remove them all
at the same time (ideally 30 minutes)
6. Use the same measuring cylinder (100±1ml) and top-pan balance (±0.01g) to measure the volume
of salt solutions and mass of the cylinders of potato tuber cells
Date:
Topic: Osmosis
Time: 1 hr
Method for collecting data
 Collect 6 x 100ml (±12.5ml) beakers. Use a 100ml (±1ml) measuring cylinder to pour into them
50ml of the six different salt (NaCl) solutions (0%, 1%, 2%, 3%, 4%, 5%). Label each beaker in
the rack using masking tape.
 Use a knife to remove the peel from a potato tuber. Using a core borer, cut 6 good cylinders from
the potato. Use a ruler to help you to cut the lengths of the cylinders so that they are the 30.0mm
long. Using a top pan balance, record the initial mass of each potato cylinder (be careful not to
muddle them up) and record the mass.

Cut each potato cylinder into 6 x 5.00mm (approx.) cylinders to increase the surface area to speed
up osmosis.

Place each set of potato cylinders into one of the 6 solutions. Leave them for as long as possible
(at least 30 minutes, but all for the same time).

Take the cylinders out of the 6 solutions and dry them with a paper towel – be careful not to mix
them up! Measure the new mass of each set of cylinders and record these values.

Share data with your class and complete a lab report.
Assessment criteria: Your will be assessed on the following criteria: Analysis and Evaluation
Data processing: To enable you to become familiar with the different types of data processing
you are expected to complete the following for this lab write-up.
Mean
Standard deviation
Correlation
Confidence intervals
ttest
I will be offering an optional “stats help” class after school on Tuesday the 22nd.
Assessment timeframe:
Lab: Monday 21st September
Stats help: Tuesday 22nd 2-3pm Rm. 121
1st draft due: Monday 28th September (HARD COPY submitted during class)
Final draft due: Sunday 4th September (HARD COPY submitted during class and turnitin)
Works Cited
Allott, A., & Mindorff, D. (2014). Biology Course Companion. Oxford: Oxford University Press.