Lab Report Testing the Effects of Changing Surcrose Concentration on Osmosis in Plant Cells

Lab Report Testing the Effects of Changing Surcrose Concentration on Osmosis in Plant Cells

Aim

To investigate the effects of changing the sucrose concentration on osmosis in plant cells.

Plan

Water passes into cells through a special type of diffusion called osmosis. Water molecules diffuse through the membrane from a weak solution into a strong solution until the concentration is the same on both sides. A membrane that allows only certain molecules to pass through is called a semi-permeable membrane. In a plant, water passes from a weak cell sap solution to an adjoining cell with a stronger solution, as water passes in, the volume of the sap vacuole increases. When a full sap vacuole presses against the cell wall, it is said to be turgid. If water that is lost is not replaced the sap vacuole shrinks and pulls on the cell wall, the cell becomes flaccid; this is known as plasmolysis.

In the cells shown below, water molecules will diffuse from the turgid cell into the flaccid cell, until the cells contain equal concentrations of cell sap.

I intend to use potatoes for my investigation because these are sufficiently large, to enable all cores to be taken from the same potato, which will assist in ensuring a fair test.

The concentration of sap in the sap vacuole of a potato cell is approximately

10% - 15%. I intend to place a predefined weight of potato cells (0.15g) in varying concentrations of sucrose solution (0%, 20%, 40%, 60%, 80%), to see the effects of osmosis in the cells of a potato in varying levels of sucrose solution. The potato cores will be prepared, weighed and then placed in the solution and left for a certain amount of time, they will then be removed, re-weighed and the difference in weights calc...

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...e the graph falls more steeply, flattening off at higher concentrations. I would also like to conduct an investigation, in conjunction with this experiment, to calculate the concentration of sap within the vacuole.

To do this, I would find between which parameters the curve crosses the x-axis of sucrose concentration and retest at every 1% between these two parameters until I have found the concentration which contains a core that neither gains nor loses mass. This osmotic concentration would be the equivalent of the sap in the vacuole.

As an extension to this investigation, I would run two experiments in parallel. All cores would be from the same potato, but one would run for an hour, as this one did and for the other the cores would be left in the solutions for longer, perhaps 24 hours, to establish if one hour is the end point of the osmotic diffusion.