Investigation of Osmosis in Plant Tissue

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Investigation of Osmosis in Plant Tissue

Aim

To investigate factors which affect the rate of osmosis.

The main factors which affect osmosis are:

Pressure

Temperature

Surface area

Solute Concentration

Plant Tissue

We will be investigating solute concentration as this is the easiest

factor to measure and will give us the most accurate results. We will

mainly investigate the different rate of osmosis when potato cells are

placed in solution with different solute concentrations. We are going

to use potatoes as they have homologues cells (all their cells are the

same).

Preliminary work

We investigated the rate of osmosis of potato cylinders left in

different solute concentrations.

Our hypothesis was that Rate of osmosis is proportional to the

difference in water potential inside and outside the cell.

Water potential(y) indicates which way water will move in a system.

Water will always move from a high y to a low y. y can be measured in

Kilopascals (kPa). Pure water has a y of 0 kPa. As solute is added, y

is reduced (it becomes a negative number.)

e.g.

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This is useful because you can add pressure to the equation.

If a pressure of 400 kPa is added to B (due to squeezing), the

equation is

-1000 + 400 = -600

-600 = -600

Now that the forces are equal, there will be no water movement.

We will measure y using Molar Concentration which has a concentration

of 0 - 1. Pure water has a y of 0M.

Using ’Biology, a functional approach’ by MBV ROBERTS, we deduced that

the y of a potato cell º 0.27M.

The water potential inside the cell is 0.27 M. I predict that there

will be the lowest rate of osmosis at this point and it will get

higher as the solute concentration levels move further away from

0.27M. The rate of osmosis will be higher when there is a greater

difference in water potential.

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