Final answer:
Lazzaro Spallanzani's experiments significantly impacted the theory of biogenesis by providing evidence that life does not spontaneously arise from nonliving matter but requires pre-existing life, challenging the previously held belief in spontaneous generation.
Step-by-step explanation:
Lazzaro Spallanzani's experiment was a crucial part of the scientific challenge against the theory of spontaneous generation, which suggested that life could arise from nonliving matter. By conducting his experiment, Spallanzani sought to disprove the findings of John Needham, who had claimed to provide support for spontaneous generation. Spallanzani boiled broths in flasks, sealed some of them, and left others open to the air. The sealed flasks did not exhibit microbial growth, suggesting that life (microorganisms, in this case) did not spontaneously arise but was introduced from the external environment. Needham had argued that a "life force" was necessary for spontaneous generation, and this life force was destroyed during Spallanzani's extended boiling. By sealing the flasks afterwards, Spallanzani was said to have prevented this vital force from entering and initiating life. Spallanzani's careful experimentation paved the way for further refutation of spontaneous generation and reinforced the theory of biogenesis, which states that life originates from pre-existing life. This work laid foundational aspects for the formulation of the modern germ theory of disease.