Question

multiple choice question ions that use specific protein channels in the membrane to move down their concentration gradient across the plasma membrane are said to cross the membrane by
o active transport
o simple diffusion
o osmosis
o facilitated diffusion

Explanation:

Facilitated diffusion uses specific protein channels (carrier proteins or ion - channel proteins) to move substances (including ions) down their concentration gradient across the plasma membrane. Osmosis is the diffusion of water across a semi - permeable membrane. Simple diffusion is the movement of small, non - polar molecules down their concentration gradient without the help of proteins. Active transport moves substances against their concentration gradient and requires energy and often specific transport proteins, but it's not moving down the concentration gradient as described in the question.

Answer:

A. facilitated diffusion