The Phosphate Transport System in Bacteria Imports Phosphate into the Cell

The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane-more acidic outside the cell than inside the cell. Phosphate transport is an example of

A) passive diffusion.
B) facilitated diffusion.
C) active transport.
D) cotransport.
E) receptor-mediated endocytosis.