Question

discovering penicillin
in 1928, bacteriologist alexander fleming was studying staphylococcus, a type of bacteria that can cause serious infections. he grew the bacteria in small containers called petri dishes. one day he noticed that mold had accidentally been introduced into one of the petri dishes and was startled to see that there were no bacteria around the moldy area. fleming correctly deduced that the mold had had an antibacterial effect; somehow it had prevented the bacteria from growing. fleming identified the mold as the strain penicillium notatum and called its antibacterial ingredient—which he was unable to successfully extract—penicillin. flemings discovery of penicillins unique effect led to the eventual finding that it could be used to treat infections. several years after his initial observation, scientists built on his work by extracting penicillin from mold and demonstrating its effectiveness as a treatment.
what is the main, or central, idea of the passage?
fleming came up with the name for penicillin, the bacteria - fighting ingredient in the penicillium notatum mold.
flemings chance observation of the antibacterial properties of mold led to the discovery of penicillin as a treatment.
fleming noticed that when a strain of mold inadvertently came into contact with a petri dish, the mold prevented bacterial growth.

Explanation:

The passage starts by introducing Fleming's study of bacteria. Then it details his accidental observation of mold preventing bacterial growth, his identification of the mold and naming of penicillin. Finally, it mentions that his discovery led to penicillin being used as a treatment. The key points are the chance observation (mold's antibacterial property) and the outcome (penicillin as a treatment).

Answer:

Fleming's chance observation of the antibacterial properties of mold led to the discovery of penicillin as a treatment.