To investigate the effect that a varied concentration of solution has on the osmotic activity between the solution and potato cylinders.

G.c.s.e Coursework: Osmosis

Aim: To investigate the effect that a varied concentration of solution has on the osmotic activity between the solution and potato cylinders.

Hypothesis:

Osmosis is a special type of diffusion. It occurs in plants when a weak solution is separated from a stronger one by a semi-permeable membrane, such as a cell wall. Water always flows from the weak solution to the strong one. This then dilutes the strong solution. This process is what moves water throughout the cells of the plant. The membrane has small holes, which only allow smaller molecules to pass through, such as water molecules, but blocks larger molecules, such as sugar molecules. This process continues until the molecules reaches an area of equilibrium. This means that the molecules are distributed evenly throughout the object, meaning that there is no higher or lower concentration. This water is than lost through the plants leaves as water vapour, known as transpiration.

I predict that for this experiment that a potato in a lower concentration of solution will increase in mass more than a potato in a high concentration of solution. My reason for this prediction is because when osmosis occurs, water transfers from a low concentration to a high concentration, i.e. when water molecules move to the plant from the water itself. So when the potato is in a low concentration, more osmotic activity will occur as opposed to a potato in a high concentration, where the activity will be smaller because the difference between the concentration in the potato and solution is smaller. Another reason is that plant cells have very strong walls. When the plant absorbs water through osmosis, they begin to swell but the cell walls prevent them from bursting. But when you put a plant in a dilute solution, these cells become turgid. This means they become swollen and hard. This works against osmosis because the pressure within the cell builds up so much that no more water can enter the cell.

Apparatus:

Cutting Tile- to protect the work surface

Cork Borer-to cut out the potato cylinders

Potatoes

Measuring cylinder-to measure the solution

Distilled Water

Electronic scale-to weigh the potato cylinders before and after the experiment.

Different concentrations of sucrose-for the experiment

Method:

To begin with, we shall obtain 12 cylinders of potato by using the cork borer. They should be quite similar in length and size. We then measure the weight of each cylinder individual, making note of each cylinders weight. Then we use the measuring cylinder to measure 6 different solutions and pour the solutions into 6 ...