Mineral Nutrition — BIOLOGY STD 11 Science — Question

Mechanism of Absorption of Elements:

1. The process of absorption can be demarcated into two main phases.
2. In the first phase, an initial rapid uptake of ions into the free space' or 'outer space' of cells - the apoplast, is passive.
3. In the second phase of uptake, the ions are taken in slowly into the inner space' - the symplast of the cells.
4. The passive movement of ions into the apoplast usually occurs through ion- channels, the transmembrane proteins that function as selective pores.
5. On the other hand, the entry or exit of ions to and from the symplast requires the expenditure of metabolic energy.
6. The inward movement of ions into the cells is influx and the outward movement is eflux.

Translocation of Solutes: Mineral salts are translocated through xylem along with the ascending stream of water, which is pulled up through the plant by transpirational pull. Analysis of xylem sap shows the presence of mineral salts in it. Use of radioisotopes of mineral elements also substantiates the view that they are transported through the xylem.