How do unicellular organisms living in water control the entry and exit of water?

Osmosis and vesicle transport

Explanation:

Osmosis is the movement of water from a low concentrated solution (hypotonic) to a higher concentrated solution (hypertonic) through a semipermeable membrane. The cells regulate the movement of water by regulating the amount of osmotically active molecules in their protoplasm. This way they can influence the flow of water into or out of the cells

For larger unicellular cells such as amoeba, where osmosis alone would not be effective, they use vesicle transport. Excess water in the cell accumulates in a vessicle that transports and expels it outside the cell.

air enters through the nose, moves through the nasal cavity, the pharynx, the larynx, enters the trachea, moves through the bronchi andbronchioles till the alveoli.