Osmotic pressure is the pressure required to stop the flow of water through a semipermeable membrane, which allows only certain molecules to pass. This phenomenon occurs when two solutions with different concentrations are separated by such a membrane. Water naturally moves from the area of lower solute concentration to the area of higher solute concentration to balance the concentrations on both sides. In biological systems, osmotic pressure is crucial for maintaining cell integrity and function. For example, in plant cells, osmotic pressure helps keep cells turgid, allowing them to maintain structure and support. In human cells, it regulates fluid balance, ensuring that cells neither swell excessively nor shrink.