To investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato chip of a given size.

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Biology Coursework 2003

Osmosis in Potatoes

By Chantelle Wright 10 B

PLANING

Before actually planning the experiment, I will do some research to find out about osmosis, and matters related to it, so that I can make predictions. And figure out a way to make this investigation fair and safe.

Planning ahead would help me find out how to do what and when, which should lead me to good results at the end of the experiment.

Aim

To investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato chip of a given size.

Background Knowledge

Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what makes the green parts of the plant "stand up" into the sunlight.

When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid."  This is the exact opposite of "turgid".  The content of the potato cells shrinks and pulls away from the cell wall.  These cells are said to be plasmolysed. 

When plant cells are placed in a solution, which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity.  We call this incipient plasmolysis.  "Incipient" means, "about to be".

    -Taken from http://arbl.cvmbs.colostate.edu/hbooks/cmb/cells/pmemb/osmosis.html

Variables: 

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.  This will give me a vary varied set of results from which I hope to make a decent conclusion.  If any of the non-variables below were not kept constant it would mean it would not be a fair test.  For instance if one of the potato chips was 1cm longer the surface area of the chip would be larger and there would therefore be more space for osmosis to occur. The variables of the experiment are as followed:

  • For the purpose of my experiment I am going to do all the experiments at room temperature to make sure it is a fair test so that I will get accurate results. 
  • To keep the water potential of the potato initially will be kept the same by using the same type of potato, which have been treated in the same way, e.g. have all been cut without being washed and peeled.
  • The mass of the potato is a dependent variable, and this means that it will be measured throughout the experiment. I will measure the mass in grams. The potato chip will be measured before it is put in the solution, and after. This will allow us to see whether osmosis has taken place, and to what extent.
  • The volume of the solution that the potato chips are kept in must be fair. The must be totally covered in the solution, and the amount of solution will be kept the same because all the potato chips are the same size.
  • I am also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between scales.

This table below tell us the variables and the non-variables in the experiment:

Fair Test

Fair testing should play a big part in this experiment. If this experiment is not a fair test, we will be obtaining the wrong results, which could lead us to the wrong conclusions.

First of all, and most importantly, we will have to get the measurements of the solutions and the weights of the potatoes as exact, and as accurate as possible. We will try and get the measurements of the potatoes as accurate as possible for every single potato, evenly cutting the potato pieces, and making a record of the length to the nearest millimetre. And I will be using a ruler so that we can get the best readings possible.

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But I believe one of the most important steps in the fair testing is to make sure that the potato is fully covered by the solution. This is because the potato should fully submerge, by having total contact with the solution so that osmosis can take place in the whole of the potato slice and not just the part that is submerge.

When using the scales, we will make sure that the balance is reading zero, before we put the potato pieces on it. This is so that we do not get a false reading, with the weight of our ...

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