Saturday, March 28, 2009

run and tumble

03.20.09. Many bacteria forage for nutrients using a "run and tumble" strategy: they swim straight ("run") until they detect a decrease in nutrient concentration, then they spin around ("tumble") to face a new direction and try again. Students were shown a demo of a running-and-tumbling bacterium whose jagged path was labeled with length measurements, then asked, "How far would the bacterium have had to swim if it went in a straight line instead?" With a bit of guidance ("Do you see the triangles?"), students recognized this as an application of the Pythagorean theorem, and that the answer lay in summing several hypotenuse calculations.