Mechanism of Absorption of Elements
The inward movement of ions into cells is called influx, and the outward movement is called efflux.
The process of absorption includes two main phases:
- First phase: Initial rapid and passive uptake of ions into the apoplast (free space or outer space) of cells, usually through ion channels (trans-membrane proteins that function as selective pores).
- Second phase: Slow uptake of ions into the symplast (inner space or cytoplasm) of cells, which is an active process requiring energy.
Translocation of Solutes
Mineral salts are translocated through the xylem along with the ascending stream of water.
Analysis of xylem sap shows the presence of mineral salts, and the use of radioisotopes of mineral elements confirms their transport through the xylem.
Soil as Reservoir of Essential Elements
Weathering and breakdown of rocks enrich the soil with dissolved ions and inorganic salts.
Roles of soil:
- Supplies minerals and holds water.
- Harbours nitrogen-fixing bacteria and other microbes.
- Supplies air to the roots.
- Acts as a matrix that stabilizes the plant.
Deficiency of essential minerals affects crop yield, so fertilizers containing both macro- and micro-nutrients should be supplied.