A few questions about cells?

Semi-permeable simply means certain things are allowed in or out of cell and this is determined by the cell's membrane. The cell membrane is considered an organelle hence its job is to control what comes in and out of cell. If the cell membrane loses control over what comes in and out, the cell will die. It will die because they use concentration gradients and their pive energy to get things into cell, too much and the cell explodes. Hence, the concentration gradient from high concentration will move to low volume concentration wheather it be liquid (osmosis) or solute (sodium), i.e. diffusion.