The answer is that a unicellular organism would swell and burst.
In a hypotonic solution the water concentration of the cell's cytoplasm is lower then that of the hypotonic solution. If unicellular organism is exposed to a hypotonic solution, the water from the solution will enter the organism by the process called osmosis. The aim is to balance water concentration on the inside and outside of the organism. But, that water entering the cytoplasm of the cell will make pressure on the cell membrane. If the excess water cannot be removed from the organism, it will swell and burst.
Because each part does a unique step in the system. An example would be that the mouth and stomach breakdown the food, but the small and large intestine absorb nutrients and water into the bloodstream.
