Explanation:

Water moves across the cell membrane by a process called osmosis. Osmosis is the movement of water molecules from an area of high water concentration to an area of low water concentration through a selectively permeable membrane.

How osmosis works:
- Water molecules move across the cell membrane through special protein channels called aquaporins.
- Aquaporins allow water molecules to pass through the membrane while preventing the passage of other molecules.
- The direction of water movement is determined by the concentration of solutes (particles) on either side of the membrane.
- If the concentration of solutes is higher outside the cell (hypertonic solution), water will move out of the cell, causing it to shrink.
- If the concentration of solutes is higher inside the cell (hypotonic solution), water will move into the cell, causing it to swell.
- If the concentrations of solutes are equal on both sides of the membrane (isotonic solution), there will be no net movement of water.

Significance of osmosis:
- Osmosis is essential for maintaining the balance of water inside and outside the cell.
- It helps in regulating cell volume and preventing excessive swelling or shrinking.
- Osmosis plays a crucial role in various biological processes, including nutrient uptake, waste removal, and cell communication.

In conclusion, osmosis is the process by which water moves across the cell membrane, ensuring the proper functioning and survival of cells.