Water is transported across cell membranes primarily through osmosis and facilitated diffusion.
Osmosis: Passive Transport of Water
- Osmosis is a type of passive transport.
- It involves the movement of water molecules across a semi-permeable membrane.
- Water moves from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).
- The membrane is not permeable to the solute, only to water.
Facilitated Diffusion
- Facilitated diffusion is another form of passive transport, as mentioned in the reference material.
- While the reference does not explicitly detail water transport via facilitated diffusion, it is known that specific protein channels, called aquaporins, facilitate the rapid movement of water across cell membranes.
- Aquaporins significantly increase the permeability of the membrane to water, speeding up the process.
Summary Table: Water Transport
| Transport Mechanism | Energy Required | Direction of Movement | Role of Membrane Proteins |
|---|---|---|---|
| Osmosis | No | High water concentration (low solute) to low water concentration (high solute) | None |
| Facilitated Diffusion | No | High water concentration to low water concentration (facilitated by aquaporins - membrane protein) | Aquaporins |
