Phosphate Ion Has the Structure PO₄³⁻

Phosphate ion has the structure PO₄³⁻.This ion is reversibly added to and removed from many different protein molecules in the cell as a means of regulating the proteins' functions.Water's solvent properties are important in understanding the modification of proteins by phosphate ion because

A) biochemists use water as the solvent in laboratory experiments aimed at mimicking the internal workings of a cell.
B) when proteins are removed from cells and placed in solvents from the lab, their functions change.
C) the external cell environment is composed of water, and many signaling molecules move through aqueous environments to bind to receptors on cell surfaces.
D) the internal cell environment is composed of water, and all cellular reactions occur within this aqueous solvent.
E) the phosphate ion has different solubilities in different solvents.