Question

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 osmosis
c active transport
d phagocytosis
e the work of an ion pump

Explanation:

Facilitated diffusion is a passive - transport process. It occurs along a concentration gradient and is faster than simple diffusion due to the help of transport proteins (channels or carriers), without using metabolic energy. Osmosis is the diffusion of water. Active transport requires energy. Pinocytosis is a form of endocytosis which also requires energy. The Na - K pump is an example of active transport and uses energy.

Answer:

A. facilitated diffusion