Answer the following question given this paragraph: 

Passive transport is a way that small molecules or ions move across the cell membrane without input of energy by the cell. The three main kinds of passive transport are diffusion, osmosis, and facilitated diffusion.


Q: In passive transport, small molecules or ions move across the cell membrane without requiring input of what?

 Choices:

- pressure

- water

- heating

- energy

A:
energy
