Osmosis and the living cell

Osmosis is the movement of water across a cell membrane. Water moves toward the side with more dissolved particles, helping balance the water on both sides.

Hypotonic

A solution with fewer dissolved particles than a normal cell. Water moves in and the cell swells.

Isotonic

A solution with the same amount as a normal cell. The cell stays the same size.

Hypertonic

A solution with more dissolved particles than a normal cell. Water moves out and the cell shrinks.

For example:

• A raisin placed in water plumps up because water moves into its many dried-out cells.
• A red blood cell placed in pure water can swell and burst because too much water moves into the cell.
• Plant cells take in water from the soil by osmosis. As water enters the cells, they become firm, which helps support the plant’s stems and leaves.