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Tuber Cells

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  • October 1999
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DETERMINATION OF THE WATER POTENTIAL OF POTATO TUBER CELLS.

Method.

Five sucrose solutions with varying molarity and one control containing distilled water were prepared and poured into test tubes. The potato discs were dried, weighed and added to the test tubes. The discs were then weighed again after a period of 24 hours. The percentage change in mass was then calculated.

Apparatus.

 Specimen tubes with stoppers x6

 1cm3 diameter cork borer

 razor blade

 filter papers

 balance

 distilled water

 sucrose solutions with varying concentrations

 potato cut into small discs

Results. (Fig 1.0)

Sucrose concentration (M)Initial mass

(kg)Final mass

(kg)Change in mass

(%)

0.100.951.2531.57

0.200.941.1320.21

0.301.031.1511.65

0.400.951.0510.52

0.500.880.86-2.27

0.600.930.84-9.67

Control0.991.4042.41

Discussion.

Osmosis is the passive diffusion of water molecules across a selectively permeable membrane from a down a concentration gradient. The water potential of a system is the tendency for water to exit the system. In this experiment the aim was to measure the tendency for water to leave the tuber cells. As the water potential of pure water is zero the concentration of sucrose in solution will have an effect on the water potential, this is called the solute potential. The greater the concentration of sucrose the more negative the water potential, because water moves from a high to low water potential.

When the potato is put into water it contains solute molecules which draw water in providing the external solute concentration is lower. The more solute molecules present the lower the water potential such change is referred to as the solute potential. To find the water potential of the cells we need to find out at which concentration of sucrose solutions was a state of equilibrium obtained, i.e....