Question

On which surface of cell, Donnan equilibrium occurs
A. Cell Wall
B. Plasma Membrane
C. Transport
D. Nuclear Membrane

Answer 1

Hint: Donnan equilibrium describes the equilibrium that exists between the two solutions that are separated by a membrane.

Complete Answer:
Donnan Equilibrium: Donnan equilibrium is also called Gibbs-Donnan effect, Donnan law, Donna’s effect, or Gibbs-Donnan equilibrium. It was proposed by American physicist named Josiah Willard Gibbs in 1878.
- Donnan Equilibrium was named after Frederick George Donnan, he was the one who proved its existence in biological cells.
- Plasma membrane is selectively permeable that means it allows the passage of some ions through it and it also doesn’t allow some ions to pass through it.
- Donnan effect describes the behavior of charged particles that sometimes fail to distribute evenly across the two sides of the plasma membrane near the semipermeable membrane i.e. plasma membrane.
- This is because of the presence of different charged substances i.e. positively charged substances and negatively charged substances.
- These differently charged particles are unable to pass through the plasma membrane and thus create an uneven distribution of charged particles across the both sides of the membrane.
- The solutions may be gel solutions of electrolytes or colloids. The electric potential arising between two solutions is called the Donnan potential.
- Donnan equilibrium is the equilibrium at which the ion concentration on either side of the membrane becomes static.

Hence, option B is the right answer for this question.

Note: Donnan equilibrium is one of the mechanisms of mineral absorption in plant roots. There are some ions present inside the root cells which are called indiffusible ions or fixed ions. These ions do not diffuse outside through the plasma membrane. If a cell has cations as fixed ions, such a cell can absorb anions from the soil in order to maintain electrical potential balance. The absorption of anions causes Donnan equilibrium of anions and cations. By attaining equilibrium the root cells can absorb any mineral in their ionic form.