In the lunchroom one day, a student notices a cell phone lying on the floor in a dirty corner.  she picks it up and quickly drops it when she sees a layer of disgusting mold on the underside, on the screen of the phone. “Ewwwww!” She wonders, does bacteria or mold grow on cell phones normally? What surface of cell phones has the most bacteria, the front or the back, or is there a difference? She gingerly handles her own cell phone as she surfs The Internet and search of answers to her questions. While reading about bacteria and cell phone surfaces, she learns how to culture bacteria on petri plates and discovers that it is quite easy to buy plates and sterile cotton swabs to use in an experiment.  she uses some of her birthday money to purchase some supplies and decides to perform an experiment. She decides to design her experiment to answer the question: what surface of cell phones has the most different types of bacteria present? She thinks that the screen of the cell phone, which is most often pressed against the users cheek, will have a greater variety of bacteria present. The student gather sterile petri plates and cotton swabs and ask several of her classmates To let her take samples from their phones. She swaps the front and back of each phone and rubs his wives on their own sterile petri plates. She leaves the petri dishes at room temperature over a week and records what she sees. She writes down the number of bacterial colonies that girl, what color the colonies are, and whether mode also grows on the petri plates. At the end of a week, she examines her data. She finds that on average, there are more colonies that grow from the samples collected from the front of the phones, but there is a lot of mold that grows on all the plates, making the bacterial colonies hard to count. She concludes that her experiment was inconclusive and that more study is needed to support or reject her hypothesis. She wonders if there is a way to reduce the amount of mold that grows on the plates, to give her a better chance of accurately counting bacterial colonies.
1. List 2 problems with her experiment’s design.
2. How would you design a better experiment to answer her scientific question?
