When a substance moves across the plasma membrane along a concentration gradient at a rate faster than would be expected by simple diffusion alone but without the expenditure of metabolic energy, the process is best described as:

A. Facilitated diffusion
B. active transport
C. pinocytosis
D. the work of an ion pump
E. Osmosis

A. Facilitated diffusion

Explanation:

The plasma membrane is an important membrane that is present in the cell and plays an important role in the exchange of the materials across the cell. This membrane is made up of phospholipid bilayers and some other components. Movement of the substances across the membrane takes place by two methods such as an active process in which the energy required and the other is the passive process in which energy is not required.Diffusion, osmosis, and facilitated diffusion are an example of passive diffusion. Facilitated diffusion is such type of passive movement in which the membrane proteins helps in the transport of the substances across the membrane and thus the is faster than other passive processes. In this process no energy is required and movements take place along the concentration gradient.