USA Biology Olympiad (USABO) Practice Exam

The movement of ions from an area of higher concentration to an area of lower concentration through a channel protein is known as?

1. Active transport

2. Facilitated diffusion

3. Simple diffusion

4. Osmosis

The correct answer is: Facilitated diffusion

The movement of ions from an area of higher concentration to an area of lower concentration through a channel protein is referred to as facilitated diffusion. This process involves the use of channel proteins, which are integral membrane proteins that help transport ions and polar molecules across the cell membrane without the expenditure of energy. Facilitated diffusion is a passive transport mechanism, meaning that it relies on the concentration gradient of the ions, allowing them to move naturally toward the area of lower concentration. This differs from active transport, where energy is required to move substances against their concentration gradient. Simple diffusion does not involve channel proteins and typically applies to small, nonpolar molecules passing directly through the lipid bilayer. Osmosis specifically pertains to the movement of water molecules through a partly permeable membrane and is not applicable to the transport of ions. Thus, facilitated diffusion accurately describes the ion transport process outlined in the question.