All Movement, Including That of Diffusing Molecules, Requires a Small

Multiple Choice

All movement, including that of diffusing molecules, requires a small expenditure of energy; what is the source of the energy that makes diffusion across the cell membrane possible?

A) Cells hydrolyze ATP to provide the energy for diffusion.
B) A small percentage of the diffusing molecules react chemically with the membrane.
C) Thermal energy is present in the extracellular environment.
D) Gravity forces the molecules to move downhill.