Describe the manner in which indirect active transport depend on direct active transport.
The Correct Answer and Explanation is:
Correct Answer:
Indirect active transport depends on direct active transport because it uses the concentration gradients established by direct active transport to move other substances across the membrane against their own concentration gradients.
Explanation
In cells, substances must often move across membranes against their concentration gradients, a process that requires energy. This is where active transport plays a critical role. There are two main types of active transport: direct (primary) active transport and indirect (secondary) active transport.
Direct active transport uses energy directly from ATP to move ions or molecules against their gradients. A well-known example is the sodium-potassium pump (Na⁺/K⁺-ATPase), which uses ATP to move sodium ions out of the cell and potassium ions into the cell. This creates a steep concentration gradient of sodium outside the cell and potassium inside.
Indirect active transport does not use ATP directly. Instead, it relies on the gradients created by direct active transport. In particular, the sodium gradient generated by the sodium-potassium pump is commonly used. This gradient stores potential energy, which can then be harnessed to transport other substances.
For instance, in the intestinal cells, the sodium-glucose co-transporter uses the sodium gradient to bring glucose into the cell against its own gradient. Sodium moves back into the cell along its gradient (from high to low concentration), and glucose is carried along with it (against its gradient). The energy for this process comes from the sodium gradient, which was established by the sodium-potassium pump using ATP.
Therefore, indirect active transport is fully dependent on direct active transport because it requires the electrochemical gradients that are set up by ATP-powered pumps. Without the initial work done by direct active transport, the gradients would not exist, and indirect transport would not occur. This cooperative system allows cells to efficiently move a variety of substances using minimal energy input.
