Question

On which surface of the cell Donnan equilibrium occurs?
(a) Cell wall
(b) Tonoplast
(c) Plasma membrane
(d) Nuclear membrane

Answer 1

Hint: Gibb-Donnan effect is seen in layers that are semi-permeable which is used as a physiological application in dialysis, neurology, etc.

Complete answer:
Near the semipermeable membrane, the behavior of charged particles sometimes fails to evenly distribute across both sides of the membrane. It is called the Gibbs-Donnan effect. The most common cause is the presence of differently charged particles that are unable to cross the membrane resulting in an uneven electrical charge. The plasma membrane in the cell is a semi-permeable layer where Donnan equilibrium occurs.

Additional information:
- In blood plasma, large anionic proteins are not permeable to the walls of capillaries because small cations are attracted but are not protein-bound, small anions cross walls of capillary away from anionic proteins more steadily from cations.
- Thus, some ionic species cannot pass barriers while others can pass the barriers.
- The solutions may be electrolyte solutions or gels or colloids as such the boundary phase between gels and liquid or gels also act as a selective barrier.
- The electric potential that occur between these two solutions is called Donnan potential
- Gibbs-Donnan effect is named after Josiah William Gibbs an American physicist and Fredrik G.Donnan a British chemist.
- Josiah William Gibbs proposed this theory and G.Donnan studies it experimentally.

So, the correct answer is 'plasma membrane '.

Note:
-In the triphasic model for articular cartilage, Donnan equilibrium is prominent. This model was proposed by Mow and Lai.
-Donnan equilibrium is also used in electrochemical fuel cells and dialysis.
In red blood cells and in neurology, this effect is used as a physiological application.