Question

which phrase best defines diffusion?
active transport of particles up a concentration gradient
movement of particles from a region of low concentration to a region of high concentration
movement through a cell membrane using energy from atp
movement of particles from a region of high concentration to a region of low concentration

Explanation:

Diffusion is a passive transport process (no energy from ATP or active transport involved) where particles move down the concentration gradient, i.e., from high to low concentration. The first option is wrong as diffusion is passive, not active. The second option describes movement against the gradient (which is active transport like pumps), and the third involves energy (ATP) which is active transport. Only the last option matches the definition of diffusion.

Answer:

D. movement of particles from a region of high concentration to a region of low concentration (assuming the last option is labeled D; if the original labels were different, adjust the identifier, but based on the options, the correct one is the last option with that description)