In the early twentieth century, what was Alexander Fleming's hypothesis concerning the relationship between a yellow-green mold and certain strains of bacteria?

a. He thought the bacteria had released a chemical that caused the mold to grow. b. He thought the bacteria fed on the mold, causing it to shrink and disappear.

c. He thought the mold had released a chemical that prevented the bacteria's growth.

The correct answer is the option c) He thought the mold had released a chemical that prevented the bacteria's growth.

Explanation:

In the 1920s, Alexander Fleming was working in his laboratory at St. Mary's Hospital in London when, almost by accident, he discovered a naturally growing substance that could attack certain bacteria. In one of his experiments, Fleming observed that colonies of a bacterium had been depleted or removed by a mold that grew on the same Petri dish. He observed that the bacteria furthest from the fungus had grown to produce large-sized colonies, while the colonies closest to the fungus were tiny. He determined that mold made a substance that could dissolve bacteria. The fungus was penicilium chrysogenum and thus Fleming called this substance penicillin, by the name of the mold that produces it. Thus, after several years of experiments in 1930, Howard Florey and Ernest Chain developed at Oxford University the procedures to produce pure penicillin from the fungus that Fleming isolated. Thus penicillin could be concentrated by Florey and Chain, and in 1945 they shared with Fleming the Nobel Prize in Medicine.

Then, the correct answer is the option c) He thought the mold had released a chemical that prevented the bacteria's growth.