Active Absorption of Ions (Part Three)

ATPase Mediated Transport

ATPase can also generate proton gradient across the membrane. ATPase helps in hydrolysis of ATP. ATP is broken down into ADP and inorganic phosphate (Pi) with the addition of water. Water is spilt up into H⁺ and OH^-. Then cations are transported activity in exchange for H⁺ in a direction opposite to H⁺. Anions follow passively, if anions are transported activity in exchange for OH^-, cations show passive movement.

Ionic Uptake by Roots

Ions are present in the soil either adsorbed to the clay micelles or free in the soil solution. The uptake of ions by roots can be explained by the following theories:

• Contact Exchange Theory.
• Carbonic Acid Exchange Theory.

Contact Exchange Theory

According to this theory, the ions adsorbed on the clay micelles get adsorbed to the root in exchange for H⁺ ions, previously, adsorbed on the root.

Ions adsorbed on solid particles oscillate within a small space.

When two particles are close enough, the oscillation space of an ion adsorbed to one particle overlaps the oscillation space of an ion adsorbed to another particle. Thus exchange of ions may take place.

Carbonic Acid Exchange Theory

The soil solution provides medium for exchange of ions between the root and clay micelles.

Carbon dioxide released in respiration of root forms carbonic acid by reacting with water of the soil solution.

CO₂ + H₂O → H₂CO₃ → H⁺ + HCO^-₃

Carbonic acid then dissociates in the soil solution to form H⁺ and HCO^-₃ ions shown above expression. H⁺ ions are adsorbed to the clay micelles in exchange for cations, such as K⁺, which are released into the soil solution. From here they may diffuse to the root, where they may be adsorbed in exchange for H⁺ ions.

Related posts:

1. Mechanism of Ionic Uptake – Active Absorption of Ions (Part One) Active Absorption of Ions The active transport of ions into...
2. Mechanism of Ionic Uptake – Passive Absorption of Ions Ions may be taken up by the plant cells by...
3. Composition of the Soil (Part Two) Clay Minerals and Cation Exchange The clay particles are composed...
4. Active Absorption of Ions (Part Two) Cytochrome Pump This mechanism of ion transport is based on...
5. Entry of Water into Roots Water diffuses directly from the soil into the free space...