Question

In the early days of germ theory, contagious diseases were thought to be caused only by fungi or bacteria. In the 1890s, Dmitri Ivanovski filtered extracts from diseased tobacco plants and discovered that the disease could be transmitted to new plants through the filtrate. He hypothesized that something smaller than bacteria or fungi was responsible for the transmission of the disease.

Which best explains how Ivanovski’s work led to a change in the germ theory?
He tried to promote his hypothesis as a law.
He used a new experimental method to test his hypothesis.
He used a more powerful bacterial strain than other scientists had.
He obtained results that confirmed what other scientists were thinking.

Answer 1

He used a new experimental method to test his hypothesis.

Ivanovski’s filtration experiments showed the infectious agent passed through filters that trapped bacteria, demonstrating a new class of pathogens (viruses) smaller than bacteria and expanding germ theory beyond fungi and bacteria.