The driving force for transport is a chemical potential difference caused by differing concentrations on either side of a membrane, rather than a chemical potential difference between different chemical species. Material flows from one region to another, rather than from one chemical species to another. Like enzymes, membrane transporters can facilitate this material exchange without being consumed by the process.
Passive transport occurs down a solute s concentration gradient.
Active transport of a solute against it s chemical potential difference is possible if the transport is coupled to another source of energy. This could be a chemical reaction, or another transport process.