7.3 Passive Transport

Passive transport is diffusion of a substance across a membrane with no energy involved. Diffusion is the movement of molecules of any substance so that they spread out evenly into the available space. 
The movement of particles will flow from high concentration to low concentration. Note, to go from low to high you need energy in the from of ATP to move the solute against its concentration gradient.
Osmosis is the diffusion of water through a semi-permeable membrane. This is especially important when the solute particles are too big to flow through the membrane. In this case the water moves to equalize the concentrations.

Tonicity is the ability of the surrounding solution to cause a cell to gain or lose water.

There are many examples of diffusion, some of which include proteins, and this process is vital to cell function and overall health.




Tim Barber