Practical assesment about biology: To determine the water potential of potato tuber cells

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OSMOSIS

Aim

To determine the water potential of potato tuber cells.

Background knowledge

Osmosis is defined as the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. Osmosis is considered in terms of water potential and solute potential.

Water potential is a measure of the kinetic energy of water molecules. Here, water molecules are constantly moving in a random fashion. Some of them collides with cell membrane, cell wall, creating a pressure on it known as water potential. The higher their kinetic energy the more they move and hits the membrane, therefore higher the water potential. Water potential also depends on the number of molecules of
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If the solution surrounding a cell has the same solute concentration as the cell then water will pass equally between them. When a solution has the same solute concentration as the cell then it is described as isotonic.

Starch is insoluble in water because it is formed when many monosaccharide condense together to form long chains. As it is long chain polymers and complex carbohydrates, the bonds which hold them together are hard to be broken down by water. Therefore starch is insoluble in water. Sucrose is soluble in water because it is a disaccharide sugar. These sugars are formed when two hexose sugar molecules react together by condensation reaction. When water is added in this sugar, it is broken down into hexose sugar (small unit), as bonds holding the disaccharide sugar are spitted up by water.

Preliminary Work

I did an experiment using sweet potato and sucrose solution. I measured the change in length and the change in mass of the sweet potato. The results are shown below:

The table below shows the volume of water and sucrose solution used to make dilutions

Concentration

(M)Volume of sucrose (ml)Volume of water (ml)Total volume

(ml)

0 0100100

0.22080100

0.44060100

0.66040100

0.88020100

1.01000100

Length change

Concentration (M)Length at start (mm)Length at end (mm)Change in length(mm)Length change (%)

0303226.67

0.23029-1-3.33

0.4303000.00

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