An Investigation into factors affecting Osmosis in Potato Tissue

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Faizal Patel                                                   5/3/2007

An Investigation into factors affecting Osmosis in Potato Tissue

PLAN

I am investigating the factors which directly affect the process of osmosis. I will be using potato tissue and sugar solutions to do this.

Osmosis is the process by which water molecules move from one cell to another, in living systems, across a partially permeable membrane, from a region of high water concentration to a region of low water concentration. A partially permeable membrane allows small molecules like water to pass through it, but does not allow larger molecules like glucose to pass through it.

Aim: My aim is to investigate the effect osmosis has on the mass and length of potato tissue and to investigate what effect varying the concentration of the sucrose solution surrounding the potato tissue, has on it. I also intend on working out the isotonic point, the point where osmosis does not occur because there is no net movement of water because the concentration on the outside of the potato, is the same as that on the inside.

To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed.  I have chosen to vary the concentration of the sugar solution surrounding the potato tissue. The following factors are those which I must keep constant throughout the experiment as they may affect osmosis:

• Temperature- I will perform the experiment at room temperature.

• Cultivar of potato.

• Length, surface area and volume of potato chips- I will use Vernier callipers.

• Angle potatos are cut in- I will cut them at right angles.

• Age of potato.

• The storage of the potato prior to its’ use.

• The volume of the sugar solution- I will choose a volume and use a measuring cylinder to measure it out every time.

• The time the potato is left in the solution.

Apparatus: white tile, top pan balance, scalpel, Vernier calipers, cork borer, potatoes, thermometer, distilled water, sucrose, stop clock, beakers, paper towels, ruler.

Method: 

  1. Use the cork borer to cut 21 identical cylinders out of the potatoes.
  2. Place the potatoes on the white tile and use the scalpel to cut the ends (at right angles), so that they are all the same length (use Vernier callipers).
  3. Make sure all the cylinders are of the same length and diameter and note the length down.
  4. Divide the potato cylinders into 7 sets of 3, and weigh their masses (to 2 decimal places) using the top pan balance, and note this down.
  5. Prepare 25cm³ of 7 sucrose solutions of different sucrose concentrations- use 0, 0.1, 0.2, 0.4, 0.6, 0.8, and 1 molar solutions, and fill 7 beakers with these solutions. The following dilution table shows how to prepare these concentrations of sucrose solution using distilled water and sucrose:

(NB-I have decided to experiment with an extra concentration of solution- 0.1, as this is near the value I believe to be the isotonic point.)

  1. Place 1 set of 3 potato cylinders in each beaker at exactly the same time, and start the stop clock. Make sure that the potato cylinders are completely covered by the sucrose solutions.
  2. Label the beakers according to what molar solution they contain, and the mass of the potato cylinders in them.
  3. After 20 minutes remove the potato cylinders from the beakers and place them (in their sets) on paper towels.
  4. Dry them gently using the paper towels to remove any solution on the surface.
  5. Measure their lengths using the Vernier calipers and weigh their masses using the top pan balance, and note these values down.
  6. Use the thermometer throughout the experiment to make sure that it is staying constant.
  7. Repeat the whole experiment 3 times, and present your results in a table.
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The following is a diagram showing how the apparatus should be set up:

 

In terms of safety, I must make sure that I am very careful with the scalpel as it may be very sharp, and I must also make sure that I do not drink any of the sucrose solutions.

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