When designing an experiment to address a specific question, remember to
Š plan the system that you will use, including organisms, equipment and techniques, as completely as possible so that you will have all of your materials ready when it’s time to do the experiment.
Š identify the independent variable - what treatment you will vary or manipulate? This should come from the question you are asking.
Š identify the variables that you will control (keep constant) and make a plan for how to keep them constant.
Š identify the dependent variable - what you will measure.
Š include a negative control - a sample that is put through a ‘mock treatment’, treated with water, or not expected to change for some other reason. Almost every experiment should have a negative control.
Š include a positive control - a sample that you know will show the effect you are measuring - to be sure that your detection system works. Positive controls are usually appropriate to include in your experiment.
Š consider how you will replicate the experiment to verify your results. That might mean running samples in duplicate or triplicate, or perhaps comparing your results with those of another group doing the same thing.
Š describe how you will carry out the experiment - in outline or flow chart form.
Š note what data you will record (what you will actually measure) and make a table for collecting data in advance.
Š consider how you will analyze the data.
Š state a hypothesis or prediction and consider how your results will support or contradict your prediction.
One, Two, Three, Four...
How many individual bacteria make up a single colony? In the space below, design an experiment to address the question using the techniques we have learned so far—including the spectrophotometer. Be sure to include all the elements of a good experiment (including controls of course!) and address the assumptions embedded in your experimental design.