Osmosis is driven by

Options

A. Concentration of dissolved solutes in a solution
B. Pressure difference
C. Membrane composition
D. Both (1) and (2)

Answer

To answer the question "Osmosis is driven by," we need to analyze the factors that influence the process of osmosis. Here’s a step-by-step breakdown of the solution:

### Step-by-Step Solution:

1. **Understanding Osmosis**:
- Osmosis is the movement of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

2. **Identifying the Driving Forces**:
- The primary driving force for osmosis is the concentration gradient of solutes. Water moves to balance the solute concentrations on both sides of the membrane.

3. **Concentration of Dissolved Solutes**:
- When there is a difference in solute concentration between two solutions, water will move from the area with lower solute concentration (more water) to the area with higher solute concentration (less water). This is the essence of osmosis.

4. **Pressure Difference**:
- Another factor that can influence osmosis is the pressure difference across the membrane. This pressure can affect the movement of water, especially in biological systems where turgor pressure is significant.

5. **Membrane Composition**:
- While the composition of the membrane (selectively permeable) is important for osmosis to occur, it does not drive the process. It simply allows for the selective movement of water.

6. **Conclusion**:
- Therefore, osmosis is driven by both the concentration of dissolved solutes in a solution and the pressure difference across the membrane. The correct answer is that osmosis is driven by "both first and second."

### Final Answer:
Osmosis is driven by both the concentration of dissolved solutes in a solution and pressure difference.