Looking at the over all picture of the membrane the term fluid mosaic should become evident. Uniport - one molecule moves in only one direction. Symport - Two different molecules moving in only one direction. Antiport - Two molecules moving in opposite directions. The net directional movement is away from the center of concentration.
Diffusion is the net movement down the concentration gradient.
In a solution of many different substances each substance diffuses down its own concentration gradient independent of the others. Diffusion is a passive type of transport, it requires no additional energy to make it work. Osmosis is diffusion of water across a biological membrane. Water is usually the solvent, hence the term aqueous solution. If a cell from a salt water fish is placed in a beaker of fresh water, the cell is said to be hyperosmotic to the water.