Population Ecology with bacteria

The growth of bacterial colonies can be effective as a model of human population growth. A petri dish with suitable nutrients (e.g. agar) can be "seeded" by something as simple as having the students cough or sneeze on the dish. Keeping in mind that once a bacteria colony becomes visible to the human eye, the densities of bacteria are of the order of 100 million (108) per square centimeter

Today your group will be given a petri dish seed with bacteria. You will measure the total number of bacteria per unit time at the start of each class period for one week straight. When you come into class, the first thing you will do is record the size of a selected colony of bacteria. Copy down the following chart and fill in the data each day.

There are 10,000 bacteria per square millimeter. Day Diameter of colony (mm) Area (πr2) # of Bacteria 1   2 3 4 5

Questions? Do you see an exponentially increasing rate or a linearly increasing rate? What eventually limits the growth of the bacterial colony? How can this possibly represent or model the human population? Did your colony of bacteria encounter any environmental pressures? Did your colony reach a carrying capacity? If so, what induced the carrying capacity?

Homework Graph your data and answer your questions on the back side of the paper.