Table of Contents

• Section 1. How the meningitis population grows
• 1: How many meningococci can kill you?
• 2: Build the basic growth equation
• 3: Draw exponential growth
• Section 2. So why isn't Frank dead already?
• 4: How long has poor Frank got?
• 5: All we need now is data
• 6: Looking at data
• 7: Log transform straightens out exponential growth
• 8: Do ALL curves get "straightened" by taking the log?
• 9: Phases of bacterial growth
• Section 3. How can we tell when the population is growing exponentially?
• 10: A test for exponential growth
• 11: And the answer is...
• 12: No way its growing that fast!
• 13: Some more practice
• 14: Extended problem: Exponential growth ends
• 15: Review

And the answer is...

Pretty clever so far... but the whole reason we got this data in the first place was to figure out how fast the bacteria can double, and so far we still haven't managed to do that.

If we look at the actual data again, we can see that we weren't lucky enough to ever observe the actual number doubling, so that won't help.

We can determine doubling time roughly by reading it off a graph. To do this, pick a starting population (on the y axis) which falls within the exponential growth window. Find the doubled population and check that it also falls within the exponential growth window. Find the amount of time elapsed (on the x axis) between the two population readings. This is the approximate doubling time. (Note: it's a little hard to find the doubled population because this is a log-transformed graph. The applet will help you with this.)

Look at the graph again and follow the directions to find the actual doubling time.

Hooray! Now we know! The doubling time was about 27 minutes.

To recap, 21 generations gets us to a deadly dose of bacteria.

And each generation lasts 27 minutes.

So Frank should be dead in .... 21*27 = 567 minutes, or about 10 hours.

Dum - dum - DUM - DUMMMMM....