Final answer:
Pasteur used the swan-neck flask design to ensure that microorganisms in the flask had food and oxygen. The twists and bends of the flask's neck allowed for air exchange while preventing the entry of any airborne microorganisms. Pasteur's experiments showed that the swan-neck design effectively prevented contamination and microbial growth in the flask.
Step-by-step explanation:
Pasteur made sure that any microorganisms that appeared in the flask had food and oxygen by using his swan-neck flask design. The long, twisted neck of the flask allowed for air exchange with the outside, allowing oxygen to enter the flask. However, the twists and bends of the neck prevented the entry of any airborne microorganisms, ensuring that they did not have access to the broth inside the flask.
To test his hypothesis, Pasteur conducted two parts of the experiment. In the first part, he boiled the broth in the flask to sterilize it. When the broth was cooled, it remained free of contamination, demonstrating that the swan-neck design prevented the entry of microorganisms. In the second part of the experiment, he boiled the flask and then broke off the neck, allowing microorganisms to be introduced. As a result, the broth became contaminated and microorganisms started to grow.