Osmosis Investigation

If the solution surrounding the plant cell is more concentrated than the cell itself the water is taken from the cell until the cell becomes plasmolysed. When the cell becomes plasmolysed it can no longer support itself as it has too little water and the cell becomes quite limp. This is also called exosmosis.

The concentration gradient is the way in which the molecules move. In osmosis water tends to move down the water concentration gradient.

Control Variables;

My control variables are; the size of the potato, the temperature of the solutions, the volume of the outside solutions and the length of time the potato cylinders are left in the solutions.

Independent Variable;

My independent variable is the concentration or molarity of the outside solutions.

Dependent Variables;

My dependent variables are the volume of the potato cylinders and the mass of the potato cylinders.

PRACTICAL PROCEDURE

Apparatus;

For this experiment we will be using a pipette filler, a cork borer, test tubes (5), a test tube rack, a potato, different molarities of solution ( 0, 0.2, 0.4, 0.6, 0.8 ), filter paper, scales, a scalpel, a ruler and a beaker.

Method;

First we put the test tubes into the test tube rack. We then put 10ml of each concentration of the solutions into each test tube using the pipette filler. We bore cylinders out of the potato and cut them into 2cm lengths. We weigh the potato cylinders, with the scales, before putting them into the separate test tubes. We record the weights to work out the mass changes in the end. We leave the potato cylinders in the different concentrations of solutions for one week. We take the potato cylinders out of the test tubes and weigh them again. To find the change in mass we subtracted the starting mass from the end mass.

This is how the different concentrations were made;

We will record the results in a table like the following;

We will record the results under the following graph headings;

Prediction;

I predict that in the potato cylinder in test tube 1 will take in water through its cell membrane it will increase in mass. The potato cylinder in the test tube 2 will lose very little water through exosmosis. The potato cylinder in test tube 3 will lose more water than the potato cylinder in test tube 2 but not as much water as the potato cylinder in test tube 4. The potato cylinder in test tube 5 will lose the most water out of the 5 test tubes. The reason I think this is because the potato is more concentrated than the solution in test tube 1 and this results in endosmosis to take place. The potato cylinders in the other solution are less concentrated than the solutions because the solutions have got stronger and they get stronger as the test tube number goes up. A change in mass will occur because the potato cylinders lose or take in water from the surrounding solutions.

Results;

These are the results for my group;

These are the results for the class average;