You probably noticed the curvy line on the original graph turned into a straight line on the
log transformed graph.
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Why does this happen? Consider the following 2 facts:
1. As you increase a log by 1, you’re increasing the magnitude of the original measurement by a factor of 10.
2. When you allow an additional unit of time to go by (in this case, half a day), you’re allowing the bacteria to increase by a factor of 10.
Taking the log accounts for the multiplying nature of bacterial growth and all you’re left with on the
graph is a straight line, pointing upwards.
When growth happens by multiplying the population by a constant number each timestep, we call that
exponential growth. Any time you have exponential growth, taking the log of the population size will turn
the graph into a straight line. This is true even if the constant multiplier is not 10 — in that case, your straight line will
have a different slope, but it will still be straight.