Question

The theory explaining passive absorption of mineral salts is :

• A. Ion exchange
• B. Carrier Concept
• C. Cytochrome pump theory
• D. None of the above.

Answer 1

The correct option is A Ion exchange

a) Ion exchange theory: The exchange of anions or cations of the cells with the ions of the same and equivalent charge of the outer solution is called ion exchange. Ion change does not require metabolic energy. Therefore, it is a passive physical process. Thus it is not affected by the rate of aerobic respiration. Two theories explaining the mechanism of ion exchange. These, are 1) contact exchange theory and (ii) Carbonic acid exchange theory

b) Carrier concept: In this, the carrier protein picks up an ion from one side of the membrane to the other side. The picking up and discharge of the ion require energy. The energy is obtained by the hydrolysis of ATP.

c) Cytochrome pump theory: Anions could be transported across the membrane by the cytochrome system. Energy is supplied by the direct oxidation of the respiratory intermediates.

From the above theories, both the carrier concept and the cytochrome pump theory are the active absorption whereas the ion-exchange theory is the passive absorption. So, the correct option is A.