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

Draw exponential growth

Hopefully at this point in your career as a biology student, you have seen a graph of exponential growth. Rather than show you a picture right away, use your mouse to draw an exponential curve (specifically, starting at 1 and doubling at each timestep) on the graph below.

Then click on the "graph" button to see how close you got.

 

So, on regular graph paper, exponential growth looks like a curve heading up (or accelerating). When a few meningococci double, that only gives us a few more. But when thousands of meningococci double, we get thousands more. When a million double, we get a million more.

Pretty soon we've got a real infection going on.

(Note for people who are way ahead: In a few screens we'll find out that the graph-on-regular-paper doesn't work very well when talking about bacteria, and we'll fix that problem. But we're not there yet.)