There are two types of transport in this regard: (1) passive transport and (2) active transport. Passive transport is a kind of transport by which ions or molecules move along a concentration gradient, which means movement from an area of higher concentration to an area of lower concentration. Examples of passive transport include diffusion, filtration, and osmosis. Active transport is a kind of transport wherein ions or molecules move against a concentration gradient, which means movement in the direction opposite that of diffusion – or –movement from an area of lower concentration to an area of higher concentration. This type of transport requires expenditure of energy and the assistance of proteins (i.e. carrier protein).