Here's a breakdown:

* Passive transport: This type of transport relies on the concentration gradient of a substance to move it across the cell membrane. It doesn't require the cell to expend energy. Think of it like a ball rolling downhill - it doesn't need any extra force to move.

Here are some examples of passive transport:

* Simple diffusion: Movement of a substance from an area of high concentration to an area of low concentration.

* Facilitated diffusion: Movement of a substance across the cell membrane with the help of a protein channel, still following the concentration gradient.

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

In contrast to passive transport, active transport requires the cell to expend energy (usually in the form of ATP) to move a substance across the cell membrane, often against its concentration gradient.