Test how the molarity of a water/sucrose solution affects osmosis in potatoes.

Variables

The things that will change are:

• The molarity of each solution and this will change by increasing the amount of sucrose as the amount of water decreases, keeping the total volume the same

Equipment

The equipment needed for this task is:

• 3 x clean test tubes
• 9 x 1cm of Valor potato
• 1 x Scalpel
• 100ml of 0.0M, 0.25M, 0.50M, 0.75M, 1.0M sucrose solution
• 1 x Top Pan Balance Scale
• 5 x Filter paper
• 1 x Test tube stand
• 5 x Metal Paperclips
• 1 x Measuring Cylinder
• 1 x Paper Towel

Health & Safety

For health & safety we made sure that there were paper towels easily to hand in order to mop up any spilt liquids. When we had finished the experiment we placed the used solutions into a plastic bucket and wrapped the potatoes in the paper towel before putting them in the bin. We did not feel the risk was great enough to warrant the use of safety goggles.  

Method

First, I got a Valor potato and cut it into 1cm strips using a sharp knife. I then measured the potato and cut it into 1cm cubes. Then I measured the mass of a potato cube using the scales. Before I weighed a cube I had to remove excess surface moisture using the paper towel.

I then measured out the 5 different Molar solutions using the measuring cylinder. The amount of water/sucrose in each solution is shown in this table.

I placed 3 potato cubes on each paperclip, the paperclip was used to space the cubes apart so that the solution could reach each surface of the cube, giving the same surface area. I placed each paperclip in a different Molar solution. I then left each solution for 2 hours, I timed this using a standard analogue clock.

I used 3 potato cubes in each solution to make it easier to identify any anomalous results. I then used the average reading from each test tube for my results table.

I removed each paperclip from the solution and removed each potato cube from the paperclip. I then measured the size of the potato using a pair of vernier callipers and the mass of the cube using the scales.

I recorded the results in a table and then disposed of the potato cubes and solutions in a safe manner.

Results

Table to show the increase in Mass of the Valor potato cube

These results show that as the molarity of the solution gets lower the potato increases in mass by an increasing amount. This upholds my prediction

“I predict that as we lower the molarity of the solution (a solution with a higher concentration of water) the potato’s mass will increase more than with a high molarity solution (a solution with a higher concentration of sugar).”

I have also compared my results with results found on the internet. My results fit in with the results of other tests. I have also checked my results with results found using different species of potato. I gained these results from another classmate in my Biology class.

Table to show the increase in Mass of the Piper potato cube

This shows that a similar amount of increase in mass occurs as the Molarity of the solution decreases.

Conclusion

Valor potatoes increase in mass according to the molarity of a water/sucrose solution when left for 2 hours.

This is because the concentration of water inside the potato is much lower than the concentration of water in the solution. Osmosis occurs because the cell walls of potatoes are a semi-permeable membrane so the water from the solution passes through into the low concentration in the potoato.

Evaluation

I tried hard to keep the constants the same for each test tube. This was quite difficult using a scalpel. To improve this I could have used an apple corer or similar to cut a piece of potato.