Why does water enter a cell that is placed in hypotonic solution?

When a cell is placed in a hypotonic solution, water enters the cell due to osmosis. Osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. In this case, the hypotonic solution has a lower concentration of solutes compared to the inside of the cell, so water moves into the cell to equalize the concentrations.

Here's a more detailed explanation of the process:

1. Concentration Gradient: The hypotonic solution has a lower concentration of solutes, such as salts and organic molecules, compared to the inside of the cell. This creates a concentration gradient, with a higher solute concentration inside the cell and a lower solute concentration outside.

2. Semipermeable Membrane: The cell membrane is semipermeable, meaning it allows certain molecules and ions to pass through while blocking others. Water molecules can freely move across the cell membrane, while most solutes cannot.

3. Osmotic Pressure: The difference in solute concentrations between the inside and outside of the cell creates osmotic pressure. Osmotic pressure is the force that drives the movement of water across the membrane to equalize the concentrations.

4. Water Movement: As the osmotic pressure is higher outside the cell, water molecules move from the hypotonic solution into the cell. This influx of water causes the cell to expand and become turgid.

It's important to note that the extent to which water enters the cell depends on the concentration gradient and the permeability of the cell membrane. If the concentration difference is significant, the cell may experience excessive swelling and even burst, which is known as cell lysis.