2-4 Bacteria

Bacterial Growth and Populations

Supposing that you grow bacteria in a petri dish, giving them the diet they like best. These bacteria can then divide approximately once every 20 minutes, doubling their numbers in that time period.

How many bacteria would there be in the petri dish at the end of 24 hours? (Answer this before you go on to the next question—write it down on a sheet of paper)

Of course, the number of cells after one full day of growth is interesting and surprising! There is another thing we must think about when such a great number of things, no matter how small, collect in one place. Cells like the ones we are talking about weigh something. For example, suppose that each cell weighs 1.1 x 10 -15 pounds. That is .000 000 000 000 0011 pounds. That is very, very light.

First, try to guess about how many pounds of cells there would be at the end of 24 hours. Write the amount you guess on a sheet of paper.

Now try to figure out the weight of 4.3 sextillion cells after 24 hours.

If you multiplied 4,300,000,000,000,000,000,000 cells by the weight of one of them, .000 000 000 000 0011, you would find the weight after 24 hours to be 4,730,000 pounds—over four million pounds!

4,730,000 pounds is about the same weight as 1300 large cars. Surely, the building holding all those cells would buckle under all that extra weight.

The growth of the bacteria is shown in the graph. The curve rises very steeply after 11 to twelve hours.

Bacterial growth

This is called exponential growth.

We know that many things can happen to keep the cells from growing that much or we would be buried by bacteria!

Question 2.13.
Can you think of what kinds of things might happen to keep the bacteria from filling the laboratory and then the world?

Write any ideas you might have in your notebook or on paper provided by your teacher.