How does the concentration of a sucrose solution affect the rate of Osmosis in Potato Cells?

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Jennie Lace 10c

How does the concentration of a sucrose solution affect the

Rate of Osmosis in Potato Cells?

PLAN

        I have chosen to investigate how the rate of osmosis taking place in potato cylinders varies when I change the concentration of the surrounding sucrose solution.

I will vary the concentration of sucrose in the solution, and carry out various measurements on the potato cylinders before and after the experiment, to see what affect changing the concentration has had.

I predict that with the lowest concentration of sucrose, the potato will increase in mass, because of water moving into the cells.  The percentage increase will then get smaller each time I increase the concentration of sucrose in the solution.  At some point, the mass of the potato will not increase, and will be the same as it was before (when there is no net flow of water particles in or out of the potato cells).  After this, the mass of the potato will start to decrease as I keep on increasing the concentration of the sucrose solution.  At some point the potato cylinders will lose all the water that they are able to, and the percentage mass loss will stop decreasing.

This is what I expect the graph of my results to look like:

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        

Osmosis is the movement of water particles from a weak solution (a hypotonic solution) to a strong solution (a hypertonic solution.  It happens through a selectively permeable membrane, and is a type of diffusion.

In a potato, water particles travel through the cell membrane, which is a selectively permeable membrane.

During osmosis in a plant cell, the water particles move through the cell membrane and into the large vacuole, where they are stored in a solution of sugars and salts.

For this experiment, I will be using sucrose, which has large particles that cannot fit through the holes in the selectively permeable cell membrane, but water particles can fit through, as they are much smaller.

This diagram shows what happens during osmosis:

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                

The solution on the left side is hypotonic, and the one on the right is hypertonic.

The water particles will move through the cell membrane from the left side to the right side, as there are more water particles on the left than on the right.

        If the left side was the solution in the beaker, and the right was the solution in the vacuole, then water would be moving into the cell and the potato cylinder would increase in mass.

        If the left side was the vacuole and the right side was the solution in the beaker, water would move out of the cells and therefore the potato cylinder would decrease in mass.

        If the two solutions of sucrose are not the same concentration then there will be an overall net flow of water particles from the hypotonic solution to the hypertonic.  There will usually be an increase or decrease in mass, as long as all variables other than concentration of the solution are kept the same.

        However if the two solutions are the same concentration, there is no overall net flow.  Some water molecules do move through the membrane one way, but then some more will move through the other way.

        When there is no net flow of water particles, and there is no change in mass after the potato has been kept in the solution for a long period of time, the solution on the beaker and the solution in the cell vacuole are said to be ISOTONIC.

        This is a diagram of two isotonic solutions:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        

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On a graph, these changes in percentage gain or loss of mass can be shown as followed:

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        

Point A is where water particles have moved into the cell, as the concentration of sucrose in the beaker is lower than that in the vacuole, and therefore the potato cylinder will increase in mass when water moves into the vacuole.

Point B is where the two solutions are isotonic, so there is not net flow of water particles, and therefore no change in mass.

Point C is where water particles have moved out ...

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***** Great attention to detail is shown in this write up together with the use of appropriate biological terminology throughout. A few small numerical errors.