Table of Contents

• Section 1. Frank's Story
• 1: The story
• 2: Biological interlude
• Section 2. How the meningitis population grows
• 3: How many meningococci can kill you?
• 4: Build the basic growth equation
• 5: Draw exponential growth
• Section 3. So why isn't Frank dead already?
• 6: How long has poor Frank got?
• 7: All we need now is data
• 8: Looking at data
• 9: Log transform straightens out exponential growth
• 10: Do ALL curves get "straightened" by taking the log?
• 11: Phases of bacterial growth
• Section 4. How can we tell when the population is growing exponentially?
• 12: A test for exponential growth
• 13: And the answer is...
• 14: No way its growing that fast!
• 15: Some more practice
• 16: In search of ... the exact doubling time
• 17: Finding doubling time with messy numbers
• 18: Logs = Exponent-busters
• 19: Let's bust some exponents
• 20: Let's bust some exponents
• 21: Extended problem #1: Exponential growth ends (with a whimper)
• Section 5. Back to Frank
• 22: Extended Problem #2: How long DOES poor Frank have?

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.)