Question

What is osmosis?
A. The passive flow of water or any other solvent from a region of higher water concentration to a region of lower water concentration through a semipermeable membrane.
B. Active flow of water or any solvent from a region of higher water concentration to a region of lower water concentration through a semipermeable membrane.
C. The passive flow of water or any other solvent from a region of lower water concentration to a region of higher water concentration through a semipermeable membrane.
D. None of these

Answer 1

The phenomenon of osmosis was given by Pfeffer which describes the movement of a solvent across a semipermeable membrane.

Complete answer:
Osmosis is the migration of solvent molecules from a hypertonic solution i.e. solution with less concentration to a hypertonic solution i.e. solution with more concentration through a semipermeable membrane to keep the concentration equal. It can be defined through the concept of free energy levels of the solvent molecules. Semipermeable membrane is a thin barrier in between of two solutions allowing the components of the solutions, generally the solvent to move.

In osmosis the solvent molecules pass from a solution of lower concentration to a solution of higher concentration through semipermeable membranes. It takes place without any expenditure of energy. It is generally of 2 types:
-Exocytosises: It is the case when the water moves out of the cell due to hypertonic solution present outside. It causes the protoplasm to shrink and exit the cell wall.
-Endosmosis: It is the case when the water enters the cell due to a hypotonic solution present outside the cell. It is known as plasmolysis and it helps in restoring the turgidity of cells.
Osmotic pressure is the pressure which must be applied to in order to prevent the passage of solvent due to osmosis. The factors that control osmosis are: The concentration of the dissolved solutes in the solution and the pressure difference between the solutions.

Hence, the correct answer is option (A).

Note: Reverse osmosis involves applying additional pressure to the water so that it moves from hypertonic solution to hypotonic solution. By this method salts can be removed from the saline water.