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The effect of temperature on the survival of yeast cells

Asked by blueflames72 | Mar 20, 2007 | AS Level > Biology > Coursework
blueflames72 asks:

I need to plan an investigation to find the lowest temperature that kills all the yeast cells in a suspension of either dried or fresh baker's yeast. How would i go about doing this? The planning is based on the assumption that I am provided with 10% suspension of yeast, 10% solutions of sucrose and 1% methylene blue solution (indicator).

etutor answers:
Methylene blue can be used as an indicator for oxygen. levels and therefore for respiration. If the yeast uses oxygen the methylene blue turns from blue - colourless. You will need to make up a suspension of yeast in the sucrose solution and add some methylene blue. Set tubes up in different temperatures and look for the temperature in which the methylene blue stays blue. This means the yeast is dead and is not respiring

4 student responses


Essentialy, i carried out preliminary work involving this. But what should I write about it? I was asked to produced 1000 words about this experiment but I can not think of anything to include in it. Obviously i've written the method, the apparatus used etc. but what else should I include?

responded Mar 25, 2007 11:08:35 PM BST

im also doing this investigation and these are the general notes on what should be included (our teacher told us this)

for your hypothesis this needs you to back up what you think will happen using relevant sources (which you must include all referances to, as u prob already know) such as a book or an internet site. back up your hypothesis maybe draw graphs of what you predict to happen.

identify the variables being used, the independent (one that changes)  and the dependent (variable measured) as well as the variable which is/are controlled. state how the test will be kept fair.

(ur results from preliminary work should have been so you can explore the factors and variables diff concentrations etc)


for the independent variable (which in this case is temperature) give a suitable value of ranges. (For our experiment we were told we couldnt use ice, so we knew not to go below 0degrees in our temp. also baring in mind yeasts optimum temperature the temp must be below optimum if we are to find out the lowest temp at which all yeast gets killed)


for concentrations of sucrose/ glucose etc if u are changing these (it all realy depends on what your method is) you have to show how concentrations will be made.

apparatus (as you have done) and justify your reasons for choosing the apparatus (accuracy and precision, maybe safety)

Safety, which is not just stating the safety precautions, but how to avoid accidents as well, overcome the safety issues etc 

a clear Method which allows obtaining of precise results

then show a table of results (fill in the units and headings, but not the results as no experiment is actually taking place)

Finally, evaluation, which talks in detail about precision of results, how reliable results are, and whether or not they are valid. talk about how to improve method etc etc


i apologise if anything has been missed out, and hope this can help you


responded Mar 29, 2007 12:31:07 AM BST

wat quantities did u use for it? i hav to do the experiment nxt week and need to know asap

responded Apr 18, 2007 4:51:59 PM BST

hi im doing the same investigation but don't have a clue what method to use and what apparatus i will  need etc can any1 help asap plz?

responded May 6, 2007 2:16:41 PM BST
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