Expert: Walter Hintz - 4/3/2011

Question
Hi...I helped my daughter do her project on who has a cleaner mouth a dog or a human.   I cannot figure out how to make a graph of the bacteria in the petri dishes.   not sure how to determine who has the least or the most except by looking at it.

Answer
Hi Kathy
 Unless you can find out which types of bacteria are on the petri dishes you can only do a quantitative study. In other words your problem to solve has to be which mouth has more bacteria. The word "cleaner " is relative. You cannot tell which is cleaner by growing the bacteria. All you can do is count the colonies. You can make a bar graph with the two counts. If you want to conclude that fewer bacteria means a "cleaner" mouth I suppose that you can.