Amount of Sugar in a Potato

Amount of Sugar in a Potato

When you submerge a plant cell in water, water flows through the cell

wall and cell surface area into the vacuole from the outside. As a

result, the cell swells up, but does not burst. This is because the

cell wall stops the cell expanding too much. When this point is

reached we say that the cell is fully turgid. This type of diffusion

is called osmosis, and takes place through a partially permeable

membrane. The water moves from a dilute solution to a concentrated

solution. This stops when the levels of water in each solution are

equal. The experiment we are about to do will prove that osmosis takes

place, and that it takes place in a living cell. We will then attempt

to find out the percentage of sugar within a potato.

Preliminary Experiments

Viskin tubing is a special kind of membrane, as it has millions of

tiny holes in it. The experiment that we are going to do will show how

a special kind of diffusion, called osmosis occurs through a membrane

that lets small molecules through but not large molecules. This type

of membrane is known as a semi permeable membrane, or a partially

permeable membrane.

The following experiment will show that osmosis takes place.

Plan

I shall follow the following plan to complete the experiment:

* Tie one end of a viskin tube to make a bag.

* Fill the bag with 20% sucrose solution.

* Push a capillary tube into the end of the bag, and tie the bag to

the bottom of it.

* Clamp the capillary tube to a stand and lower the bag into a beaker

of water.

* Mark the level of the sucrose solution in the capillary tube.

Re-measure this level every five minutes for half an hour.

[IMAGE]

The level or water in the capillary tube will increase. This is

because water moves from a dilute solution to a concentrated solution.

There is a larger amount of water in the beaker, than in the viskin