The method of osmotic pressure comparison: look at the number of water molecules per unit volume. The more water molecules per unit volume, the lower the permeability. When the number of water molecules per unit volume is small, the osmotic pressure is high.
Extended data:
Generally speaking, the pressure generated when water enters a hypertonic solution from a hypotonic solution through a semipermeable membrane is osmotic pressure.
When the number of water molecules passing through the semi-permeable membrane from two opposite directions in unit time is equal, the permeation reaches balance and the liquid levels on both sides no longer change. Pressure caused by liquid level difference in osmotic balance.
The osmotic pressure of solution depends on the number of solute particles in unit volume solution: the more solute particles, the higher the concentration of solution, the greater the attraction to water and the higher the osmotic pressure of solution;
On the contrary, the less solute particles are, it is related to the content of inorganic salts and protein. Na+ and Cl- are the dominant inorganic salts in extracellular fluid, and more than 90% of the osmotic pressure of extracellular fluid comes from Na+ and Cl-.
At 37℃, the osmotic pressure of human plasma is about 770kPa, which is equivalent to that of intracellular fluid.