Name and briefly describe four methods in which molecules and ions may pass through a cell membrane?

A. Osmosis - the movement of water down a water potential gradient through a partially permeable membrane.
B. Diffusion - the net movement of molecules or ions down a concentration gradient.
C. Active Transport - movement of molecules or ions against the concentration gradient, which requires an input of energy from the cell.
D. Facilitated Diffusion - passive movement of molecules or ions across a cell membrane with the aid of transport proteins.