Hi there everybody!

My biology class has just completed a practical activity on osmosis. I am supposed to write a practical report for the experiment however my teacher didn't give us any questions and I have to build up by discussion page so that my report will be lengthy, so I am wondering whether anyone would be able to provide me with questions that I could put in the practical report to include, answer and consider myself. Below is what was written on my practical sheet for the experiment.

Any help/guidance from you biologists for this activity would be much appreciated and I would be eternally grateful if anyone could help me with things to think about the experiment and any complexities I need to think/consider and put in my practical report. It seems like a pretty simple experiment just involving the placement of potato discs in different sucrose concentrations for 30 mins and recording the changes in mass. What are the expected changes in mass of the potato discs that were put in a lower concentration of sucrose compared to the ones which were put in a higher concentration of sucrose? What do you guys think?
Is this a common biology experiment by the way? Anyway, I emphasize any assistance would be highly appreciated!

Introduction: This activity focuses on osmosis and the effect of different concentrations of sucrose solutions on plant (potato) cells. All substances passing into a cell have to move through a plasma membrane. The plasma membrane is partially permeable. Movement can occur via a number of processes including diffusion.

Fresh potato
Plastic ruler
Petri dishes
Measuring cylinder
Distilled water
Sucrose solutions – 0.1M, 0.2M, 0.4M, 0.6M, 0.8M, 1M
Paper towelling
Electronic balance
Felt pen

1. Label 7 Petri dishes (on lids) with the concentrations of sucrose solution.
2. (A cylinder of potato has been cut for you). Trim the ends flat so that no skin is left. Slice into 1-2 mm slices. You need 70 slices of potato for your group. Using tweezers make 7 groups of 10 slices- place gently on paper towel.
3. Weigh the first ten slices. Record the total mass of these ten slices in a table.
4. Place these ten slices into Petri dish 1 and cover slices with 30 mL sucrose solution of 0.1M. Cover dish with labelled lid and leave 30 minutes at room temperature.
5. Repeat procedure for remaining concentrations of sucrose and distilled water.
6. Carefully remove the ten slices from 0.1M solution and place on paper towel. Gently dab the top of slices to remove excess solution. Transfer to new towel when weighing.
7. Weigh the ten slices and record the mass in your table.
8. Repeat for the remaining dishes. Discard potato and clean up.
9. Calculate the change in mass and record findings in your table.
10. Also calculate the percentage increase or decrease in mass and place answers in the third column in the table.
11. Graph results (sucrose concentration x axis, %change in mass y axis). Remember you may have positive and negative changes and thus your y axis should allow for this. The graphs should be a line of best fit graph – in pencil. Remember to fully label the axes and give the graph a heading.

1 Answer

Yes, this is a common practical task and it has many variations. By plotting the results you should be able to identify the isotonic concentration of sucrose as it will not show a net gain or loss. There is still exchange but it is balanced. Make sure the axis of the graph is accuate. I can supply my class results but we used NaCl instead of sucrose - one of those variations I mentioned.