Population is expressed by an exponential growth because with every passing time interval, the population grows. Because of this fact, the population will not grow at a constant rate. Consider the following example: A population of bacteria, at hour zero, consists of only one. Every hour, the population doubles. At hour one, there are two. At hour two, there are four. At hour three, there are eight. So for every increasing hour, the population doubles, so we would express the growth by this equation:
