Category: Biology Second Paper

In 1933, scientist Lundigaard and his colleague Bersatrum introduced the theory about the absorption of mineral salts by plants called Lundigaard’s theory. According to this theory, cytochromes play an important role in the absorption of iron minerals, so it is also called the cytochrome pump theory. They observed that placing the plant in a solution of salt from water increased the respiration rate of the plant. They termed this increased respiration as anion-respiration or salt-respiration.
According to Lundigaard’s cytochrome pump theory, every cell has two compartments. Outer floor and inner floor. Protons (H+) and electrons (e+) are produced in the dehydrogenase reaction inside the cell. Protons (H+) move directly to the outer layer of the cell and combine with oxygen to form water (H2O). On the other hand, electrons (e+) enter the cytochrome chain. Inside the cell, cytochromes are oxidized by accepting electrons. After entering the cytochrome chain, electrons (e+) cycle to the outside of the cell. On the outer surface of the cell, cytochromes are oxidized by releasing electrons. Oxidized cytochrome combines with the anion (A-) located in the cell membrane to form a ‘cytochrome-anion’ compound. The anion (A-) cycles through the cytochrome chain to the intracellular surface and accumulates. An excess of anions (A-) on the inside of the cell causes an electrical-potential difference. To equalize this electric-potential difference, cations (K+) from the outer surface of the cell move directly into the inner surface of the cell. Later, cations and anions combine to meet the cell’s mineral salt needs.
Fe++ (2A-) – e- + A- → Fe+++ (3A-)

1. Active absorption requires direct metabolic energy.
2. Active absorption requires carriers.
3. Respiration rate increases during ion absorption.
4. Enzymes play an important role in ion absorption.
5. Cations and anions can be adsorbed simultaneously.
6. Ions can be adsorbed against the gradient of concentration.

The process of absorption that requires metabolic energy is called active absorption. Most mineral salts are actively absorbed by the plant body. Professor D.R. Hogland observed that the concentration of inorganic material in cells of Nitella algae is higher than the concentration of inorganic material present in water.

Some scientists Hylmo (1955) and Kramen (1956) think that when water is absorbed at a large rate during respiration, mineral salt ions are also absorbed with water. Lopushinsky observed in 1964 that the rate of ion absorption increased when the rate of transmission increased.

Proponents of ion exchange theory are Devlin (1969) and Pandey and Sinha (1972). Plant root cells contain H+ and OH-. H+ ions are released and K+ ions from the outside solution enter the cell. Similarly exchange between OH- ions and Cl- ions takes place. In this method anion exchange is least and cation exchange is most. Hence it is called cation exchange method. However, cations and anions are not adsorbed simultaneously.

Diffusion theory was introduced by Hope (1953) and Heilmo (1955). Cells of absorptive organs of plants have lower concentrations of ions and higher concentrations of ions in soil solutions. Therefore, few ions enter the cell during the diffusion process. Absorbed ions enter various cells from the cortex. The absorbed ions are then used for metabolic purposes in various cells.

Donnan introduced this theory in 1911-1914. According to this theory, there is a fixed anion or anion charge inside the cell membrane that cannot be absorbed. To neutralize this fixed negative charge, the cation or cationic charge moves in from the outside of the cell membrane in the diffusion process. This process continues until there is an equilibrium of cations and anions inside the cell. Donnan calls this phenomenon equilibrium. In Donnan equilibrium, the ratio of positive charges inside and outside the cell is equal to the ratio of negative charges inside and outside the cell.

Absorption processes that do not require metabolic energy are called passive absorption. Very small amounts of mineral salts are passively absorbed. The principles of passive absorption are:
1. Donnan equilibrium
Donnan introduced this theory in 1911-1914. According to this theory, there is a fixed anion or anion charge inside the cell membrane that cannot be absorbed. To neutralize this fixed negative charge, the cation or cationic charge moves in from the outside of the cell membrane in the diffusion process. This process continues until there is an equilibrium of cations and anions inside the cell. Donnan calls this phenomenon equilibrium. In Donnan equilibrium, the ratio of positive charges inside and outside the cell is equal to the ratio of negative charges inside and outside the cell.
2. Diffusion theory
Diffusion theory was introduced by Hope (1953) and Heilmo (1955). Cells of absorptive organs of plants have lower concentrations of ions and higher concentrations of ions in soil solutions. Therefore, few ions enter the cell during the diffusion process. Absorbed ions enter various cells from the cortex. The absorbed ions are then used for metabolic purposes in various cells.
3. Ion exchange theory
Proponents of ion exchange theory are Devlin (1969) and Pandey and Sinha (1972). Plant root cells contain H+ and OH-. H+ ions are released and K+ ions from the outside solution enter the cell. Similarly exchange between OH- ions and Cl- ions takes place. In this method anion exchange is least and cation exchange is most. Hence it is called cation exchange method. However, cations and anions are not adsorbed simultaneously.
4. Mass flow theory
Some scientists Hylmo (1955) and Kramen (1956) think that when water is absorbed at a large rate during respiration, mineral salt ions are also absorbed with water. Lopushinsky observed in 1964 that the rate of ion absorption increased when the rate of transmission increased.

The process by which mineral salts enter the cell as ions from an external source is called mineral salt absorption. The process of adsorption of inorganic salts is called ‘ion adsorption’. Mineral salt absorption process is of two types. Passive absorption and active absorption.

The source of plant mineral salt is soil water. Mineral salts are dissolved in water. However, water and mineral salt absorption are completely different processes. When mineral salts dissolve in water, they dissociate into cations (+) and anions (-). NaCl dissolves in water and dissociates into Na+ (cation) and Cl- (anion). Plants absorb mineral salts as cations and anions. Cations present in ground water are K+, Na+, Mg++, Fe+++, Zn++, Cu++, Mn++, Ca++ etc. On the other hand, anions present in ground water are NO-3, PO4—, Cl-, BO4—, PO4—, SO4– etc.
It is assumed that K+ and NO3- are absorbed most rapidly and Ca2+ and SO42 most slowly. Some ions inhibit the absorption of other ions. The presence of Ca++ and Mg++ inhibits the absorption of K+.