Get complete information on Mechanism of Absorption of Elements

Get complete information on Mechanism of Absorption of Elements

Flux:

Movement of ions

Influx:

Movement into the cell

Efflux:

The outward movement

Two ways:

1. Passive absorption:

Movement of mineral ions into root cells as a result of diffusion. Three theories:

(a) Donann’s equilibrium (Donann, 1911):

Entry of ions into the cell across the plasma membrane to maintain equilibrium is called Donann’s equilibrium.

(b) Ion exchange theory (Jenny and Overstreet, 1938):

Exchange of anions and cations absorbed to the root surface with similarly charged ions of soil solution is called as ion exchange.

(c) Mass flow/Bulk flow theory Hylmo (1955):

Movement of ions takes place through root alongwith the stream of water under the influence of transpiration.

2. Active absorption:

Uptake of mineral ions against concentration gradient. Metabolic energy is utilized for this. This energy is derived from respiration and is supplied through ATP.

Carrier concept (Van den Honert, 1937):

Some organic substances (carriers) transfer ions from outer surface to the inner surface of plasma membrane by forming carrier-ion complexes.

Cytochrome pump hypothesis (Lundegardh, 1954) explains the absorption of anions only.