I aim to find out whether osmosis happens in potatoes, and how different water concentrations affect the rate at which it happens.

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Biology Coursework -         Osmosis in Potatoes

Planning

Aim

I aim to find out whether osmosis happens in potatoes, and how different water concentrations affect the rate at which it happens.

Prediction

I predict that the weight of potato will steadily decrease as the salt water concentration increases, because less water will pass through the semi-permeable membrane. I think this because osmosis will happen more quickly as the level of concentration is at a greater difference.

Plan

In a high concentration of water the amount of solute (e.g. Salt) is low. This could be called a weak or dilute solution. In a low concentration of water the amount of solute is high. This could be called a strong or concentrated solution. When two such solutions are divided by a semi-permeable membrane, the water will move from the area of high concentration to the area of low concentration, until both sides are equal (have reached equilibrium).

Or in the words of The "Biology CGP Revision Guide"

Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration.

The first thing I needed was a partially "permeable membrane”. I knew that I could use potato or visking tubing. I wanted to opt for visking tubing as this would be more accurate, because visking tubing isn’t affected as strongly by age, and as I would be spanning my experiment over a couple of days, this could be a problem. If I was doing the experiment this way I would not be able to keep the same potato but I would have to change it for a similar one. However, unfortunately, visking tubing was not available so I had to use the potato.

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The second thing I needed was a soluble substance to alter the concentration of the water. My two initial thoughts were salt and sugar, but as potato has little sugar because it is converted into starch, I decided to go with salt.

Preliminary Test

I wasn't sure how much potato to use so I set up a preliminary test which would be designed to test which size of potato would give the largest reaction. The two main variables in this test where the thickness of the potato and the length of the potato.

To keep the test ...

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