3.2 Altering variables
You have now conducted another experiment, one which had several different variables. Variables are parts of an experiment that can be kept the same, or changed in order to test different outcomes.
In the yeast experiment, you actually performed two separate tests at the same time; one regarding the temperature and another regarding available oxygen. Note that in each case you only altered one variable (either temperature or oxygen availability).
You could repeat the yeast experiment, keeping both temperature and oxygen availability constant but altering a different variable, i.e., fixing a previously changing variable and changing a previously fixed variable. By performing a combination of these experiments the optimum conditions for yeast growth can be determined.
You should now be starting to think like an experimental scientist and considering ways that an experiment can be altered so that different hypotheses can be tested.
Takes some time now to think which other variables you could test and why.
OpenLearn - Basic science: understanding experiments 
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