Investigation Into Distinguishing Between Old and Fresh Potatoes

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Investigation Into Distinguishing Between Old and Fresh Potatoes

By Means of Osmosis

Scenario:

When buying root vegetables at a supermarket, how can you be sure that they turn over the produce correctly and that all that you buy are equally fresh?

Aim:

To determine a way of distinguishing between old and new potatoes by immersing potato pieces in different concentrations of sucrose solutions. This will enable equivalent concentrations of the two ages of potato to be found and therefore the two types identified.

Introduction:

Osmosis is a type of diffusion involving water molecules only. Osmosis can occur when there are two solutions separated by a partially permeable membrane which only allows certain molecules through. The solution on one side has a higher water potential (lower solute concentration) than the solution on the other side. This solution is described as the most hypertonic. Because, as in diffusion, water molecules move from areas of low to high solute concentration, the majority of water molecules pass through the membrane down the water potential gradient from high to low. Water molecules will continue to move across the membrane until the water potential is the same on either side. Equilibrium has then been achieved and the water level will be higher on the side which started with a lower water potential. The concentrations will then be the same and therefore isotonic.

The process of osmosis is used in plant cells to allow water into the cytoplasm without allowing dissolved substances (e.g. sugars, salts and proteins) to pass out.  The cells are covered by a cell membrane, which is partially permeable, and whether or not water passes into or out of the cell depends on the relative concentrations of the cytoplasm inside the cell and the fluid surrounding the outside.

A preliminary experiment was carried out to determine the affect that changes in water potential have on the weight of the potato. This experiment enabled us to find out what happened when the variable of sucrose concentration was changed so that for the actual experiment, the variable of the age of potato could be focused on. It also provided a suitable method to work to. This preliminary experiment provided the information that the higher concentrations of sucrose resulted in loss of weight in the potato and the lower concentrations of sucrose resulted in weight gain. Also, there was a point in-between the two extremes where there was no change in weight of the potato. This was the point where the sucrose concentration was equivalent to the concentration inside the potato.

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Sources:        Biology 1……………………………..

                

Prediction:

Taking the above information into account and looking at the two types of potato –old and new- I predict that the pieces of old potato will take in more water than the new potato. This is because the old potato isn’t as fresh and so therefore will have lost water and become shrivelled and the cells will have become flaccid. This in turn means that because water has been lost, the concentration inside the old potato is higher than that of the new potato. Because of this, I predict that when the old ...

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