When roots take up mineral ions, they are built up against their concentration gradient. both anion and cation transport utilizes an electrochemical gradient set up by proton pumps. therefore, mineral ion transport is generally considered to be:

a. diffusion

b. primary active transport

c. osmosis

d. secondary active transport?

I believe the answer is B, primary active transport. Root hair cells in plant use active transport to absorb mineral ions such as nitrates from the soil. The concentrations of minerals in the soil are lower in the soil than in within the root hair cell, therefore the transport will be against the concentration gradient which does not favor diffusion, therefore the pant has to use active transport.