Osmosis is

Options

A. Uphill transport
B. Active transport
C. Special type of facilitated diffusion
D. 1 and 3

Answer

**Step-by-Step Text Solution:**

1. **Definition of Osmosis**: Osmosis is defined as the movement of water molecules through a semi-permeable membrane from a region of higher concentration of water (or lower solute concentration) to a region of lower concentration of water (or higher solute concentration).

2. **Direction of Water Movement**: In osmosis, water moves from an area where it is more abundant (high concentration) to an area where it is less abundant (low concentration). This movement continues until equilibrium is reached, where the concentration of water is equal on both sides of the membrane.

3. **Role of Semi-Permeable Membrane**: A key feature of osmosis is that it occurs across a semi-permeable membrane. This type of membrane allows certain molecules (like water) to pass through while blocking others (like solutes).

4. **Comparison with Diffusion**: Osmosis is similar to diffusion, which is the movement of particles from an area of higher concentration to an area of lower concentration. However, osmosis specifically refers to the movement of water.

5. **Nature of Osmosis**: Osmosis is considered a passive transport process. This means that it does not require energy input from the cell; the movement of water occurs naturally due to concentration gradients.

6. **Conclusion**: Based on the definitions and characteristics outlined, osmosis can be classified as a special type of facilitated diffusion, as it involves the movement of water through a semi-permeable membrane without the use of energy.