What would happen if a cell membrane let too much water into a cell?

Animal Cell

When water moves into an animal cell (e.g. a red blood cell), the cell membrane stretches and the cell gets bigger. If this continues, the cell membrane will burst – this is called lysis.

Plant Cell

When too much water moves out of a plant cell the cell contents shrink. This pulls the cell membrane away from the cell wall. A plasmolyzed cell is unlikely to survive.

When water moves into a plant cell, the vacuole gets bigger, pushing the cell membrane against the cell wall. ... The pressure created by the cell wall stops too much water entering and prevents cell lysis. If plants do not receive enough water the cells cannot remain turgid and the plant wilts.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

The air is going to come out because of the low pressure.