Plants can only absorb soluble minerals (those that can dissolve in water). They absorb minerals dissolved in solution from the soil through their root hair cells. However, the concentration of minerals in the soil is very low. Minerals cannot be absorbed by osmosis because this is the movement of water only. They cannot be absorbed by diffusion, because the minerals are in very low concentration. Instead, active transport is used. The root hair cells have carrier molecules on their cell membranes. These pick up the mineral ions and move them across the membrane into the cell against the concentration gradient.