Osmosis is a type of passive transport.
Understanding Osmosis
Osmosis is the movement of water molecules across a selectively permeable membrane. This movement occurs from a region of high water concentration (low solute concentration) to a region of low water concentration (high solute concentration). Crucially, this process does not require energy from the cell. This is the defining characteristic of passive transport.
Several sources confirm this:
- Reference 1: Explicitly states that osmosis is a form of passive transport.
- Reference 2: While mentioning active volume regulation in cells in response to osmosis, it doesn't contradict the passive nature of osmosis itself. The cell's active response is a separate process.
- Reference 3 & 6: Clearly identify osmosis as passive diffusion.
- Reference 7: States that osmosis is a form of simple diffusion, another passive process.
- Reference 9 & 10: Reinforce that osmosis is passive transport, driven by the concentration gradient of water.
Examples of Osmosis
- Plant cells: Water moves into plant cells by osmosis, causing them to become turgid (firm).
- Animal cells: Osmosis plays a vital role in maintaining the balance of fluids in the body.
- Reverse Osmosis: A practical application where pressure is used to overcome the osmotic gradient, forcing water to move against its concentration gradient. Note that the process of osmosis itself remains passive; external pressure is applied.
Contrasting Active and Passive Transport
Unlike osmosis (passive transport), active transport requires energy (ATP) to move substances against their concentration gradient—from low concentration to high concentration. Examples include the sodium-potassium pump.
In summary, while cells might actively respond to the effects of osmosis, the movement of water during osmosis itself is a passive process.
