It relates to a pressure cooker because in a pressure cooker you can cook food at higher temperatures than under normal atmospheric pressure (like on a stove top). Once the water in which the food is boils, it undergoes the phase change from liquid to gaseous but the temperature stays the same. With pressure added, the phase change won’t happen at 100 degrees Celsius and therefore you can bring the temperature higher than the normal boiling point.
Organisms that can live in temperatures higher than 100 degrees would have to have higher pressure to prevent the water from boiling.
