Math Is Fun Forum

I know that population growth, for example, DOUBLES every time period.  Since this is the case, couldn't we use the equation y=2^x to describe DOUBLING of the population rather than the equation e^x?  Lets say a population of bacteria doubles everyday.  Lets say starting population is 2 bacteria.   Using the formula y=2^x, you get the following population growth:  day 1= 2 bacteria cells; day 2 has 4 bacteria, day 3 has 8 bacteria (and each day it doubles: 2, 4, 8, 16, 32, 64.....).  This SEEMS so perfect for the situation, BUT every text book recommends the equation e^x to describe population growth.  Why is this?  Could both equations be correct?