Final answer:
Lazzaro Spallanzani's experiments disproved spontaneous generation by showing that microorganisms in broth came from the air, not spontaneously; however, Louis Pasteur conclusively ended the debate with his swan-neck flask experiment.
Step-by-step explanation:
Lazzaro Spallanzani's experiments contributed significantly to the debate surrounding the theory of spontaneous generation, a prevalent idea until the 19th century that life could arise from nonliving matter. Spallanzani's controlled experiments involved heating broth in sealed and unsealed flasks, which demonstrated that broth in sealed flasks remained clear and free of microbial growth, suggesting that microorganisms were introduced from the air rather than generated spontaneously. This was contrary to the findings of John Needham, who believed in spontaneous generation and claimed that a "life force" was necessary for life to arise, which was supposedly destroyed in Spallanzani's boiling process. However, it was Louis Pasteur who conclusively refuted spontaneous generation with his swan-neck flask experiment. Pasteur's work not only disproved spontaneous generation but also led to the development of methods for microbial control, such as pasteurization, thus laying the groundwork for modern microbiology.