Mineral ions are often scarcer in soil water than inside a root hair cell, and yet the cell keeps taking more of them in. How does it manage that, and what does it need?

Explanation

Moving a substance into a cell against the direction it would drift by itself is exactly what active transport does, and the energy for that work is released when the cell respires. Diffusion and osmosis both run down a difference in concentration, so neither can explain uptake that carries on when the outside is the more dilute side of the membrane.