Here's a breakdown:
* Osmosis: The movement of water molecules from a region of high water concentration (low solute concentration) to a region of low water concentration (high solute concentration) across a semipermeable membrane.
* Passive process: It does not require the cell to expend energy.
* Concentration gradient: The difference in water concentration across the membrane is the driving force for osmosis. Water naturally moves to equalize the concentration on both sides of the membrane.
However:
While osmosis itself doesn't need energy, maintaining the concentration gradient that drives osmosis *can* require cellular energy. For example:
* Active transport: Cells can use energy to pump solutes across membranes, creating or maintaining concentration gradients that influence water movement.
* Maintaining cell volume: Cells need to regulate their water content to maintain their shape and function. This can involve using energy to pump water in or out of the cell, against the osmotic pressure gradient.
In summary: Osmosis is a passive process driven by the concentration gradient. While the cell doesn't directly expend energy for the movement of water during osmosis, it may need to use energy to create or maintain the concentration gradients that drive the process.
