Question

multiple choice question
what describes simple diffusion?
a substance moves up its concentration gradient.
a substance moves down its concentration gradient.
transport proteins are required.
energy in the form of atp is consumed.

Explanation:

Simple diffusion is a passive - transport process where a substance moves from an area of higher concentration to an area of lower concentration (down its concentration gradient) without the need for transport proteins or energy in the form of ATP.

Answer:

A substance moves down its concentration gradient.