In this experiment I intend to investigate the effects of osmosis on
potato cells. Specifically, I intend to use my knowledge of osmosis to
investigate the glucose concentration of the cell sap in potato cells.
Osmosis is a method by which water levels on either side of a semi
permeable membrane may balance themselves. It occurs between regions
of high water concentration and low water concentration. As it is a
special method of diffusion exclusive to water, it also allows dilute
and concentrated solutions to balance their strengths. It does this by
preventing large non-water particles from passing through the
semi-permeable membrane due to their size, in order that the water
levels on either side may equate, regardless of the solution's other
Osmosis is passive, that is to say it does not require energy in order
to be performed. This is because it occurs solely between regions of
high and low water concentration.
The direction and speed of osmosis depends on the two solutions'
osmotic potential. This is the measure of the pressure by which the
water molecules of a solution diffuse across a semi-permeable
membrane. A solution's potential is defined by its concentration. The
more soluble a solution has in it, the lower its water concentration
and the lower its osmotic potential. In the example below sugar
molecules represent the soluble.
Cell sap is contained in the vacuole of a cell and is a part glucose,
part water solution. The membrane of the cell acts as a semi-permeable
membrane across which osmosis occurs (see below). In the case of
osmosis into and out of the vacuole, it occurs across two membranes -
the plasmalemma and the tonoplast. When osmosis occurs, water may
enter or leave the vacuole according to the concentration of the
substances inside and outside the potato cell. In the example below we
see what would happen if a plant cell were surrounded by pure water.
As pure water has the highest water concentration possible, osmosis
will invariably occur into the cell vacuole, which by definition
contains a solution lower water concentration.
The plant cell will take in as much water as is needed to make
the water levels on either side of the membrane equal. As the glucose
molecules cannot pass out of the cell to equate the water levels, the
volume of cell sa...
... middle of paper ...
...order to obtain a
wider and more precise base of evidence.
There is scope for further investigation of the topic in order to
obtain further evidence and draw a more accurate conclusion. For
example, now the concentration of potato cell sap has been identified
at about 15%, a smaller range of solution strengths could be used in
an otherwise identical experiment; 5 solutions of 10% and 20%
concentration for example. Alternatively, investigations could be
conducted into the effects of osmosis on different vegetables or more
widely plants in general. For further information on the potato, the
same experiment could be conducted using samples from different parts
of the plant. This would establish whether different areas of a plant
have differing levels of sucrose in their cell sap. Any of these
suggestions would both help to support my conclusion and extend the
investigation in general further.
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