Question

Why does water move through a membrane?

Short answer

The water moves through a membrane when it is not in an equilibrium state and when it doesn’t have equal concentrations on each side of the membrane.

Step-by-step solution

Step 1. Introduction 

Like any other molecules water wants to be in an equilibrium state and also it needs an equal concentration on each side of the membrane. Osmosis is one of the processes which happen instantly to maintain an equilibrium state.

Step 2. Explanation 

Water will move quickly inside the cell when the water concentration outside the cell is more than the inside.

In case, when water enters the cell it even raises the concentration level and the reverse action will happen outside the cell if there is a lower concentration.