Hydrogen ions concentration gradient

Active Transport: The movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.

Passive Transport: The movement of biochemicals and other atomic or molecular substances across cell membranes without need for energy input.

Osmosis: A process by which molecules of a solvent tend to pass through a semipermeable membrane from less concentrated solution into more concentrated one, thus equalizing concentrations on each side.