The concentration of nitrates is often higher in

plant roots than it is in the soil around them.

Plants maintain this difference in concentration

through

(1) active transport (3) excretion

(2) diffusion

(4) coordination

(2) diffusion

Explanation:

Diffusion is a process in which molecules moves from a region of higher concentration to the region of lower concentration. In this condition, plant roots contain high concentration of nitrates than soil so nitrates moves from roots through semi-permeable to the soil by the action of diffusion until the concentration is uniform or equilibrium.