Which statement describes a uniporter transport protein?

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A uniporter is a transporter that moves a single substrate across the membrane by facilitated diffusion using a carrier protein. It binds one type of molecule, undergoes a conformational change, and releases it on the other side, and it works down the molecule’s concentration gradient without coupling to another substrate or using energy. This stands in contrast to coupled transporters: a symporter moves two or more substances in the same direction, and an antiporter moves them in opposite directions, both requiring the movement of one substrate to drive the movement of another. A channel, meanwhile, provides a pore that allows ions or water to diffuse through, rather than shuttling a single molecule via a carrier. Thus, describing a uniporter as a transport protein captures the idea of moving one kind of molecule across the membrane through a carrier-mediated, energy-independent process.