How do unicellular organisms living in water control the entry/exit of water from their cells? are they able to live in any environment? how could this be tested

A) How do unicellular organism lining in water control the entry/ exit of water from their cells? Water enters and leaves the cells depending on the concentration of the solute in both the external and internal environment of the cell or organism. The process used is called osmosis which involves the movement of water molecules depending on the concentration of solute. Water moves from a region of high water concentration to a region of low water concentration.

b) Are they able to live in any environment?
Due to the fact that water movement in and out of the cell depends on the concentration of the solute, I do not think that the organism can survive in any environment. If the organism is placed in an environment with a higher solute level, water will move out of the cell leading to dehydration and even death. 

c)How could this be tested?
The survival of unicellular organism can be tested by placing similar unicellular organism 3 containers containing different solute concentration. The first container is highly concentrated while the second container is lowly concentrated and the third is isotopic solution. leave them for thirty minutes and the observe and make a conclusion.