Plot the CFU/ml and OD numbers on your semi-log paper. Make your marks big and bold so I can see.

1. Plot the CFU/ml and OD numbers on your semi-log paper. Make your marks big and bold so I can see.

2. Clearly label your axes.

3. Add two trend lines. Make the lines different colors and bold.

– One trend line for the CFU/ml Data

– One trend line for the OD Data

USING THE CHART YOU CREATED, Calculate the doubling time of your culture. Show your work on your chart.

Select an OD between your 45-minute and 60-minute time point. Using your chart, show how the CFU/ml can be determined from your OD.

Hey! What if my data don’t make logical sense? Like, what if:

• OD is really high, but CFU/m; is really low, or
• OD is really low, but CFU/ml is high? Or
• I have OD readings greater than 2?

Graph them anyway. Really the test is about you being able to graph data and add trend lines.

Hey! My culture has a doubling time longer than 60 minutes?

Remember that you are adding a trend line, if you leave enough space on your X-axis, you can extend the trend line as far as you need too. These are just points in a 60 minute window, it is possible the log phase of your culture extends beyond this time frame, and the growth rate should not change.