Osmosis:

Osmosis is the movement of water through a selectively permeable membrane from a solution of lesser solute concentration to a solution of higher solute concentration.

Rules of osmosis and concept of tonicity of solutions:

The rules of osmosis can be best understood through the concept of tonicity of solutions. The term tonicity refers to the relative concentration of solutes in the solutions being compared.

1. Hypertonic solutions are those in which more solute is present.
2. Hypotonic are those with less solute.
3. Isotonic solutions have equal concentrations of solute.

Explanation:

In a hypertonic solution, the solute molecules attract clusters of water molecules so that fewer water molecules are free to diffuse across the membrane. On the other hand, in a hypotonic solution, there are more free water molecules and there is a net movement of water from hypotonic solution to hypertonic solution.