All Movement,including That of Diffusing Molecules,requires a Small Expenditure of Energy;

Multiple Choice

All movement,including that of diffusing molecules,requires a small expenditure of energy; which of the following small sources of energy is most likely to make diffusion possible across the cell membrane from the cell exterior into the cell interior?

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.