Final answer:
Flask A, which is unsterilized and open, would likely spoil first due to easier access for airborne microorganisms, whereas Flask B, although also unsterilized, is closed and less accessible to contaminants. In the context of endospores, Flask B with 100-year-old endospores might show more growth in a polluted medium, possibly due to a faster acquisition of resistance compared to 20-year-old endospores.
Step-by-step explanation:
If Flask A was unsterilized and open, and Flask B was unsterilized and closed, the likelihood of spoilage is higher in Flask A. The open flask allows for airborne microorganisms to enter more easily than a closed flask, leading to a faster rate of contamination and spoilage. Pasteur's experiment with swan-neck flasks illustrated this by showing that when air, but not microbes, is allowed to enter a flask, the broth remains sterile. However, once the neck is broken and microorganisms can enter, contamination occurs.
Considering the scenario with the bacterial endospores, different results might be expected in the presence of a pollutant. If we assume that Flask A contains endospores from 20 years ago and Flask B contains endospores from 100 years ago, and both are placed in a growth medium with a pollutant, we would hypothesize that Flask B might show more growth. This is based on the assumption that the older endospores, not having adapted to the recent pollutant, may acquire resistance faster or have retained some form of resistance from past exposures to different pollutants, while the younger endospores from Flask A, which was open to contamination, may be killed by the pollutant due to a lack of resistance developed in the contaminated environment of the marsh.