Ionic uptake against electrochemical gradient without the expenditure of metabolic energy can be explained by

Options

A. Ion exchange
B. Donnan equilibrium
C. Carrier proteins
D. Both (1) and (2)

Answer

To solve the question regarding ionic uptake against an electrochemical gradient without the expenditure of metabolic energy, we can break down the concepts involved step by step.

### Step-by-Step Solution:

1. **Understanding Ionic Uptake**:
- Ionic uptake refers to the process by which ions are absorbed by cells or organisms. This can occur against an electrochemical gradient, meaning that ions move from an area of lower concentration to an area of higher concentration.

2. **Electrochemical Gradient**:
- An electrochemical gradient is created when there is a difference in the concentration of ions across a membrane, as well as a difference in charge. This gradient usually requires energy to overcome.

3. **Metabolic Energy**:
- Metabolic energy (often in the form of ATP) is typically required for active transport mechanisms that move ions against their gradient. However, the question specifies uptake without the expenditure of metabolic energy.

4. **Ion Exchange**:
- Ion exchange is a process where one type of ion is exchanged for another. This can occur in solutions and does not necessarily require energy if it is facilitated by the surrounding environment or other ions.

5. **Donnan Equilibrium**:
- Donnan equilibrium refers to the state of equilibrium that exists when two solutions with different ionic compositions are separated by a semipermeable membrane. This equilibrium allows for the movement of ions without the need for energy expenditure, as it relies on the natural diffusion of ions.

6. **Evaluating the Options**:
- **Ion Exchange**: This process can occur without energy expenditure and can facilitate ionic uptake against a gradient.
- **Donnan Equilibrium**: This also allows for ionic movement without energy expenditure.
- **Carrier Proteins**: While they assist in the transport of substances across membranes, they typically require energy for active transport mechanisms, thus they do not fit the criteria of the question.

7. **Conclusion**:
- Since both ion exchange and Donnan equilibrium can explain ionic uptake against an electrochemical gradient without the expenditure of metabolic energy, the correct answer is **both 1 and 2**.

### Final Answer:
The correct answer is **option D: both 1 and 2 (ion exchange and Donnan equilibrium)**.