Here's why:

* Passive transport relies on the concentration gradient, meaning molecules move from an area of high concentration to an area of low concentration. This movement is driven by the natural tendency of systems to move towards equilibrium.

* Active transport, on the other hand, requires energy (usually ATP) to move molecules against their concentration gradient, from an area of low concentration to an area of high concentration.

Examples of passive transport include:

* Simple diffusion: The movement of molecules across a membrane from high to low concentration.

* Facilitated diffusion: The movement of molecules across a membrane with the help of a protein channel or carrier.

* Osmosis: The movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration.

Let me know if you'd like to explore any of these types of passive transport in more detail!