Final answer:
Louis Pasteur's swan-neck flask experiment conclusively disproved the theory of spontaneous generation by showing that unless microorganisms from the air were allowed to enter, sterilized broth would not develop life, laying the foundation for the germ theory of disease.
Step-by-step explanation:
The theory of spontaneous generation held that certain forms of life could arise from non-living matter. Louis Pasteur designed a set of experiments to challenge this notion.
His famous swan-neck flask experiment demonstrated that microorganisms were responsible for fermentation and spoilage, and that life does not spontaneously arise from non-living matter. Pasteur filled a flask with broth, boiled it to sterilize it, then allowed it to cool with the neck of the flask intact.
Over time, the sterilized broth remained free of microbial life, proving that without exposure to microorganisms, life would not arise spontaneously. In contrast, when he broke the neck of the flask, exposing the broth to air, it became contaminated with microbes.
This showed that microorganisms in the air, and not a 'life force,' were the source of life in the broth.
This experiment not only definitively disproved the theory of spontaneous generation but also laid the foundation for the germ theory of disease, revolutionizing the scientific understanding of life's origins and the causes of disease.