Plasmolysis is the reason. The reason that the Elodea cell prevents from collapsing completely is that the Plasmolysis is the main reason because it always has water to keep it full. The answer in this question is Plasmolysis is the reason because it always has water to keep it full.
Mercury, due to it's low gravity it would not be able to hold a very strong atmosphere.
Im not sure what the question is could u further define or give me the possible answers