Passive transport DOES NOT require the cell to directly expend ATP (the cell's energy currency).
However, it's important to understand that:
* Passive transport still relies on the pre-existing energy gradients within the cell. This means that the movement of molecules across the membrane is driven by differences in concentration, pressure, or electrical charge, which were established by the cell using energy in the past.
* Maintaining those gradients requires energy. For example, maintaining a concentration gradient across a membrane requires the cell to actively pump molecules in or out, which does use ATP.
So, while passive transport itself doesn't directly use ATP, it relies on conditions established by the cell that require energy to maintain. It's like using a pre-charged battery to power a device – the device doesn't use energy directly, but the battery needed energy to charge initially.
Let me know if you have any other questions!
