What is the definition of uniport in cellular transport?

Uniport refers specifically to a transport mechanism in cellular biology where a single molecule is transported across a membrane in one direction. This could involve either the passive movement of a substance down its concentration gradient or active transport against this gradient, depending on the energy requirements of the process.

The essence of uniport lies in its focus on the transport of only one type of molecule at a time, distinguishing it from processes like symport, which involves two molecules moving in the same direction, or antiport, which involves two molecules moving in opposite directions. Additionally, the definition of uniport is not restricted to passive transport, as it can also occur through active transport mechanisms that utilize cellular energy to move molecules against their gradient. Thus, the correct choice captures the fundamental characteristic of this transport type effectively.