Final answer:
Secondary active transport is the transport mechanism where transport of one molecule/ion against its concentration gradient is coupled with the transport of another molecule/ion down its gradient, with both moving to the same side of the membrane. Energy is indirectly provided by ATP, which maintains the necessary ion gradient driving the process.
Step-by-step explanation:
Secondary Active Transport
The membrane transport mechanism that couples the transport of one molecule or ion against its concentration gradient with the transport of another molecule or ion down its concentration gradient is called secondary active transport. In this process, both transported molecules or ions move towards the same side of the membrane.
Examples of secondary active transport include the Na+/glucose symport mechanism, where the transport of glucose against its concentration gradient is paired with the transport of sodium ions (Na+) down their electrochemical gradient.
Secondary active transport utilizes the energy stored in the gradient of the ion (usually Na+) that is moving down its gradient, which was created by a primary active transport process such as the Na+/K+ ATPase pump. This established gradient effectively drives the transport of the other substance.
Therefore, while this mode of transport does not directly use ATP to move the coupled molecule, it indirectly depends on ATP usage that maintains the ion gradient necessary for the transport mechanism.