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Topic: SNAB Biology  (Read 6164 times)

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Offline Lilly

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SNAB Biology
« on: May 08, 2008, 10:54:14 AM »
In the investigation " Effect of temperature on beetroot membrane permeability". What is the significance of calibrating the colorimeter with distilled water first?
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Offline Rabn

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Re: SNAB Biology
« Reply #1 on: May 09, 2008, 07:45:23 AM »
If I understand you correctly...the reason you would calibrate with distilled water is because cellular membranes have channels called aquaporins that allow water to be exchanged freely.  If you want to study the effects of temperature on membrane permiability you need to use a solution that minimizes any experimental error caused by the solution.  Cells have different channels that are specialized for ion transport, voltage gated channels that are effected by various ions etc...If you use a solution that contains ions and then heat the solution, you will undoubtably effect the permeability of the membrane because the molarity of the solution changes as it gets hotter.  Remember, molarity is in moles/liter, as a salt solution is heated its molarity changes because the water expands; cells work maintain an equal osmolarity with its surroundings. So if you use a salt solution to measure the effects of temperature you have to account for the change in volume and hence molarity in order to calculate the permeability.  By using distilled water, the molarity of the solution won't change with temperature and removes a complication from calculating the permeability. Using distilled water also removes any effects of the other kinds of specialized membrane channels/gates.

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