Uptake of Mineral Ions

Uptake of Mineral Ions

Unlike water, mineral nutrients cannot simply be absorbed passively by roots, for two reasons:

1. Minerals exist in the soil as electrically charged ions, and charged particles cannot cross a cell membrane unaided.
2. The concentration of a given mineral inside the root is typically already higher than in the surrounding soil solution, so straightforward passive diffusion would tend to move the mineral the wrong way — out of the root rather than in.

Because of this, most minerals must be brought into the root epidermal cells by active absorption, which consumes ATP. This active uptake of ions is itself, in part, responsible for setting up the water-potential gradient within roots that in turn drives the osmotic uptake of water. That said, some ions can also enter passively, without energy expenditure — so overall, mineral uptake is a combination of both passive and active transport, carried out by specific transport proteins embedded in the membranes of root hair cells. …