Here's why:

* Passive transport refers to the movement of substances across a cell membrane without requiring energy from the cell. This movement is driven by the concentration gradient, meaning substances move from an area of high concentration to an area of low concentration.

* Osmosis is the specific movement of water molecules across a semipermeable membrane from a region of high water concentration to a region of low water concentration. This movement is also driven by the concentration gradient, so it doesn't require the cell to expend energy.

Let me know if you'd like to know more about osmosis or other types of transport!