Question

in 1861, pasteur conducted his now - famous experiments using flasks with long necks bent into an s - shape. imagine that you are a scientist working in pasteur’s lab at this time. you decide to tip the flasks so that broth enters the long s - shaped neck. you then return the flask to its upright position. predict the most likely outcome of tipping one of pasteur’s s - necked flasks. (view available hint(s))
since the broth had been heated (effectively sterilizing it), no microbes would grow in the broth.
the broth would remain uncontaminated because no microbes could enter the long s - shaped neck of the flask.
microbes would grow in the broth because the tipping would introduce the oxygen necessary for microbial growth.
the broth would become contaminated with microbes because they were trapped in the neck.

Explanation:

Pasteur's experiment with S - necked flasks showed that microbes enter from the air. When the flask is tipped, broth entering the S - neck brings the trapped microbes (from the neck) into the broth. So the broth gets contaminated as these microbes can now grow in the broth. The first option is wrong as heating sterilized it initially but tipping introduces microbes. The second option is wrong because tipping allows microbes (trapped in the neck) to enter the broth. The third option is wrong as oxygen was already present (the flask was open to air via the S - neck), and the key is microbial contamination from the neck, not oxygen for growth.

Answer:

The broth would become contaminated with microbes because they were trapped in the neck.