Which transport process involves the bulk movement of water and dissolved substances with the water itself?

• A. Diffusion
• B. Osmosis
• C. Capillary rise
• D. Mass flow

Answer: (D)

Mass flow is the bulk transport of a fluid along with its dissolved substances, moving as a single mass driven by pressure differences in the soil–water system. This means water carries dissolved nutrients with it as it flows through pore spaces, roots, or plant vessels. It differs from diffusion, where solutes move mainly by their own concentration gradient without a sustained bulk water movement. Osmosis involves water crossing a membrane to equalize solute concentrations, but the solutes don’t ride along with the water in bulk transport. Capillary rise moves water upward due to capillary forces, not because solutes are carried with a bulk water stream. So the described process—bulk movement of water and dissolved substances with the water itself—fits mass flow.