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Using a colorimeter to measure the activity of yeast

Asked by x-lucy-89 | Apr 14, 2007 | AS Level > Biology > Coursework
x-lucy-89 asks:

i am investigating the lowest temperature that kills all the yeast cells in a sample. there are loads of questions asking about how to interpret the colorimeter readings, but should we even be using colorimeters? surely the light transmission is going to be pretty static given that the yeast has the same 'cloudiness' in each tube, regardless of the temperature. I would think that only if the tubes contained a clear liquid of different shades of blue would we be able to effectively use a colorimeter. In which case, you would need to filter the solution after the reaction has finished, but wouldn't that lose all of the indicator from the tubes anyway, seeing as methylene blue is effective on entering the yeast cells, which would be removed by filtering. Whether that is correct or not i have no idea - i just need to know whether a colorimeter would work at all and give accurate results even with the yeast in suspension?? help!

etutor answers:
The methylene blue in the solution would change colour because the yeast would extract oxygen from the solution - the methylene blue does not have to enter the yeast. There is no need to filter though, just use yeast without any methylene blue to set the zero value on the calorimeter - the calorimeter will then only measure colour, not the cloudiness of the yeast.

1 student responses


we did our preliminary work for this, this morning. apparently, if you heat up the yeast so you know it's definitely dead (ie 90% or something) and then add methylene blue, this is the colour it should be to indicate the yeast cells are dead, then if you add this as the standard for the colorimeter you can then compare your other results to it. the cloudiness doesn't affect it if your standard is the same level of cloudiness as the other tests.

responded Apr 20, 2007 5:22:28 PM BST
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