The Effect of Water Concentration on the Mass of Potato Tissue

The Effect of Water Concentration on the Mass of Potato Tissue

Aim:

The aim of this investigation is to discover the effect of water

concentration on the mass of potato tissue, and also to investigate

the movement of osmosis through potato tissue.

Scientific Knowledge:

When a substance such as a sugar dissolves in water, the sugar

molecules attract some of the water molecules and stop them moving

freely. This, in effect, reduces the concentration of water molecules.

Water Potential:

The water potential of a solution is a measure of whether it is likely

to lose or gain water molecules from another solution. A dilute

solution, with its high proportion of free water molecules, is said to

have higher water potential than a concentrated solution, because

water will flow from the dilute to the concentrated solution (from a

high potential to a low potential). Pure water has the highest

possible water potential because water molecules will flow from pure

water to any other aqueous solution, no matter how dilute.

When two such solutions (one strong, one weak) are separated by a

semi-permeable membrane the water will move from the side with more

water to the side with less until both sides are equal (have reached

equilibrium).

This can be seen in all living cells. The cell membrane in cells is

semi-permeable and the vacuole contains a sugar/salt solution. So when

a cell is placed in distilled water (high water concentration, lower

water potential) water will move across the semi-permeable membrane

into the cell (lower water concentration, higher water potential) by

osmosis, making the cell swell to carry the extra water. This cell is

now referred to as turgid. The opposite of this is where the cell

becomes flaccid, where the cell membrane actually can break away from

the cell wall. If this process were done with the potato cells I would

expect them to increase in length, volume and mass due to the extra

water.

If these potato cells were placed in a solution of low water