Investigate the effect of osmosis on the potato cylinders of a certain size in different concentrations of solution.

Equations related to Osmosis:

The osmotic pressure P of a dilute solution is approximated by the following: 

P = RT (C1 + C2 + .. + Cn)

Where R is the gas constant (0.82 liter-atmosphere/degree-mole), T is the absolute temperature, and C1 ... Cn are the molar concentrations of all solutes.

Similarly, the osmotic pressure across of membrane separating two solutions is: 

P = RT (C)

Where C is the difference in solute concentration between the two solutions.

A few key words related to osmosis:

Isotonic:        The solutions being compared have equal concentration of solutes.

Hypertonic:                 The solution with the higher concentration of solutes.

Hypotonic:                 The solution with the lower concentration of solutes

Prediction:

Upon the light of the scientific knowledge I conclude the predictions below:

In size:

Upon researching through written material on osmosis in biology, I came to the prediction that if the potato is put in a solution with less Molarity i.e. less concentration the osmotic effect would be that the water will cross the partially permeable membrane from the solution to the potato thus increasing its size; this is also true Vice-Versa.  

In mass:

 As above the prediction concerning mass derived from the knowledge received via research from books and the like is that as the Molarity in which the potato is put increases as a result increasing the concentration which would result in the transfer of water molecules from the potato to the solution thus decreasing in weight; it is also true Vice-Versa.

In turgidity:

As it was predicted that there will be increase in size it is also to be predicted that this is a result of the vacuoles filling up to their utmost (turgidity). Other than the increase in size this being true means that the potato that is bigger will also be harder. It is also true Vice-Versa.

Variables:

To produce a fair and efficient experiment I shall keep some variables constantly the same throughout the experiment and to all the potato cylinders. The variables that have to be decided by me as which will be constant and which will vary from potato cylinder to potato cylinder are:

• Solution concentration
• Surface area
• Solution volume
• Duration of experiment
• Temperature
• Type of solution
• Mass of potato cylinders

I will vary the concentration of the solution from potato to potato because the aim of the experiment is to see the effect of osmosis when allowed to process in different concentrations of solution.

I will keep the surface area the same as to minimise the probability that one potato cylinder will have more space for osmosis to take place, as this will allow a greater amount of water to pass through the partially permeable membrane in the limited time thus destroying the purpose of the experiment. For the same reason I shall keep the solution volume the same.

I will keep the duration of the experiment the same for all the potato cylinders so as to prevent one potato having more time to move molecules of water across the partially permeable membrane.

I will keep the temperature constant because osmosis could work faster in certain temperatures, due to the fact that particles move faster in hotter temperatures thus unbalancing my experiment.

I will have the same type of solution and will keep the mass of all potato cylinders the same at the start of the experiment.

Below is the finished table of the variables and non-variables:

Plan of Investigation:

I will use the concentrations 1 M, 0.8 M, 0.6 M, 0.4 M, 0.2 M, and 0.0 M (distilled water).I will use Sucrose as the solvent and I will put it in 1L of distilled water. To find out how much sucrose to use I do the following calculations keeping in mind that the Molar Mass of sucrose is 342.3g:

Concentration (M) / Volume (L) x Molarity (g)

1 M:        M/L x g        =        1/1 x 342.3        =        342.3 g

0.8 M:        M/L x g        =        0.8/1 x 342.3        =        273.84 g

0.6 M:        M/L x g        =        0.6/1 x 342.3        =        205.38 g

0.4 M:        M/L x g        =        0.4/1 x 342.3        =        136.92 g

0.2 M:        M/L x g        =        0.2/1 x 342.3        =        68.46 g

0.0 M:        M/L x g        =        0.0/1 x 342.3        =        0 g

I will use 11 cm 3 g as the volume of my potato cylinder with a mass of 10g, I will do my experiment in room temperature and the experiment will last for 50 minutes.

Apparatus:

• Stop watch – to time the experiment

• Knife – to cut the potato

• Measuring cylinder – to make solution in

• Distilled water – part of the experiment

• Sucrose - part of the experiment

• Potatoes - part of the experiment

• Stand - to support the potato

• Tissue - to place potato on after experiment

• String - to hold the potato to the stand

• Balance - to weigh the potatoes

• Beakers - where experiment will take place

• Cork borer - to cut out potato cylinders

• Ruler -  to measure the volume of the potato

Method:

1. I took two potatoes and checked to make sure they were healthy and hard

2. Using a cork borer and a ruler and I cut out potato cylinders that were 35mm long. I had to be very careful whilst cutting as the knife is very sharp. I made 6 cylinders, one for each solution.

3. Taking 6 stands I placed 6 beakers underneath them and then labelled them 0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1 M

4. Using a measuring cylinder I measured out the previously calculated amounts of sucrose solution and distilled water of which I then poured 200 ml into the beakers – each solution to its specified beaker.

5.  I then weighed every potato cylinder on an electronic balance and made sure the weights were 10g.

6.  With the help of a partner I put the 6 potato cylinders in the beakers and instantly started my stopwatch.

7. Whilst waiting for the 50 minutes to expire I set out some tissues to prevent the table from getting wet, and I drew up a basic table for my results.

8.  After the 50 minutes were over I pulled out the potato cylinders and placed all the chips on the tissues. I wrote the Molarity of the solution which the cylinders had come from on their tissues as not to confuse them with each other.

9.  I observed the potato cylinders wrote my observations and results in the observation part of this essay.

Observation:

During the experiment I observed that the potatoes in the higher concentrations of solution did not sink but floated at varying heights from the bases of the beakers, in an unmistakable pattern: The greater the concentration of the solution it was in the higher the potato cylinder was from the base of the beaker.

Upon inspecting the potato cylinders after the experiment I came up with the following observations:

1. Difference in mass:

        

 

2. In size and turgidity:

Size:

        Turgidity:

 

3.  Under the microscope:

Conclusion:

I therefore conclude upon the light of the observations from my experiment that my predictions and hypothesis were correct and that water flows from the less concentrated to the more concentrated solution, and therefore the mass increases in the more concentrated solution.

Evaluation:

Upon finishing and observing my experiment I saw flaws that could be patched in future experiments to improve the results and outcomes:

1. I could do more than one experiment for each concentration of solution and take an average of the results to increase the accuracy of the results obtained.

2. I could do experiment in another vegetable to see if the pattern of osmosis changes across different organic material.