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How to analyse the data from mythylene blue indicator?

Asked by airwish | Mar 27, 2007 | AS Level > Biology > Advice
airwish
airwish asks:

I have carried out the experiment, trying to determine the lowest temperature that kills all the yeast cells. Methylene blue solution is used as an indicator to show whether the cells are dead(stay as blue) or alive(turns colourless).
However, apart from simply looking at the solution, and recording the colour change. Is there any other ways that can be applied to obtain the results? I've tried using a colorimeter, but what roughly is the %light transmission of dead yeast cells compared to alive yeast cells?
I'm very very stuck.
I'll appreciate it greatly if you can give me some advice.
Thank you very much. :-)

etutor answers:
The colorimeter is just a more accurate way of measuring the colour of the solution - it does not tell you directly if the yeast is live or dead. You would have to measure the transmission of a suspension of boiled (therefore dead) yeast cells + methylene blue to find the reading that equivalent to no live cells. You can't just use only methylene blue, because the yeast cells themselves (even dead) will absorb SOME light.

7 student responses

x-lucy-89
x-lucy-89

I'm doing the same investiation, but i was told at one point that the colorimeter wouldn't produce the results because the solution would have to be filtered and doing that would remove the stained cells from the solution, leaving you with nothing. Does anyone know if that's right or whether if you just calibrate it with a suspension the colorimeter would work??

responded Apr 9, 2007 4:21:49 PM BST
airwish
airwish

what?never heard of that filtering process before. I'm so confused by this experiment, ok 1st lets say, this is about enzyme right? We are trying to find the lowest temp that kills all the enzymes which means yeast cells are all dead right? And to be honest, when I try the methylene blue+boiled yeast cell suspension still give u quite a big reading, and when I test the other yeast cells under diff. temp+methylene blue, they give out a random pattern. *-* HELP!

responded Apr 11, 2007 9:03:08 AM BST
x-lucy-89
x-lucy-89

what did it give a big reading on? the colorimeter?

i just meant filtering as in with a funnel and filter paper because surely the fact that the yeast suspension is cloudy has some effect on the colorimeter? as in it's not just measuring the colour - the yeast is as cloudy in all of the readings so surely the readings wouldn't show much of a difference. therefore you would have to filter it before putting it in the colorimeter, bringing with it the question: because the methylene blue stains the cells, would any colour be removed in the filtering process, therefore leaving you with a clear, but useless solution?

i'm just as confused as you are by this!!

responded Apr 12, 2007 12:33:50 PM BST
Hello99
Hello99
hey
can you help me? I'm doing the same planning exercise as you
i need to know what to wright in the introduction
e.g. what background information do i need?
thanks
responded Apr 14, 2007 5:35:59 PM BST
chigz
chigz
hi
has anyone done a pilot test? what sort of results are you getting? mine went up to about 80-90 degrees
thanks
responded Apr 14, 2007 11:40:55 PM BST
Hello99
Hello99
hey
can you help me? I'm doing the same planning exercise as you
i need to know what to wright in the introduction
e.g. what background information do i need?
thanks
responded Apr 15, 2007 11:11:49 AM BST
Hello99
Hello99
hey
can you help me? I'm doing the same planning exercise as you
i need to know what to wright in the introduction
e.g. what background information do i need?
thanks
responded Apr 15, 2007 12:10:36 PM BST
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