Microorganisms include bacteria, microscopic fungi and many protists. They differ in cellular structure and nutrition, so one set of growth conditions does not suit every microorganism. Temperature, water availability, nutrients, pH and waste accumulation can affect growth. Under suitable conditions, repeated binary fission produces exponential bacterial population increase.
For a constant doubling time, population after k doublings equals starting population ×2ᵏ. Divide elapsed time by doubling time to find k when complete rounds are specified. Real cultures cannot sustain exponential growth indefinitely: resources become limiting and wastes accumulate. A plotted population plateau indicates little net increase, not necessarily that every cell has stopped dividing or died.
Example 1
A population starts at 200 and doubles every 30 minutes. Find the population after 90 minutes, assuming no losses.
3090=3 doublings; 200×23=1600.
Example 2
Counts at 0,1,2 and 3 hours are 100,200,400 and 800. Identify the doubling time.
The count doubles at each one-hour interval, so the doubling time is one hour over this period.
Watch out: Nutrients, space, water, pH and waste accumulation can limit growth even at a suitable temperature.