Exponential growth ends (with a whimper)
Here’s a second set of data on bacteria growth rates. Your instructions are
1) to determine the exponential growth rate of the bacteria, and
2) to determine when growth stops being exponential.
| Time (min) | No. of cells |
|---|---|
| 0 | 4.3 × 106 |
| 20 | 9.7 x 106 |
| 40 | 22 x 106 |
| 60 | 48 x 106 |
| 80 | 97 x 106 |
| 100 | 116 x 106 |
| 120 | 118 x 106 |
| 140 | 67 x 106 |
Just look at the data first… what can you see with your bare eyes, so to speak?
About doubling time:
About the general shape of the population trajectory:
About when growth begins to slow down:
Now try plotting the data. (Applet may take several seconds to load).
Which time period showed exponential growth:
Let’s look at an untransformed graph to figure out the doubling time. We could do this on the log-transformed graph above, but its difficult because the y-axis is on a log scale.
Where should we start, and what is the growth rate?