Answer:
Theory of spontaneous generation.
Step-by-step explanation:
Theory of spontaneous generation stated, life arose from non-living things. Pasteur disprove this theory by S-shaped tube experiment. He used swan-neck flasks (twisted necks) and filled them with sterilized beef broth. This allowed entry of air to the flasks from outside, but not microorganisms.
In these sterilized flasks, microorganisms did not grow as there was no entry of airborne microbes. But if the necks were broken, microorganisms entered and allowed growth of microorganisms.
Thus, Pasteur proved life comes from pre-existing life and disproved theory of spontaneous generation.