Question

read the passage.
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 noticed that when a strain of mold inadvertently came into contact
with a petri dish, the mold prevented bacterial growth.
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.

Explanation:

The passage begins with Fleming's accidental observation of mold preventing bacterial growth in a petri dish. It then details his identification of the mold strain (Penicillium notatum) and the subsequent work by other scientists. The key is that Fleming's initial chance observation (of the mold's antibacterial properties) was the starting - point, and this led to the discovery of penicillin as a treatment. The first option only focuses on the observation part and not the discovery outcome. The second option is about naming penicillin, which is a minor detail compared to the overall discovery process. The third option encompasses both the observation (chance discovery of mold's antibacterial properties) and the result (penicillin as a treatment).

Answer:

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