Final answer:
Symports and antiports are types of secondary active transport systems that move molecules against their concentration gradients by utilizing the energy from proton gradients (DpH) and membrane potential differences (ΔY). Symporters move substances together in the same direction, while antiporters move them in opposite directions. These mechanisms can concentrate molecules where they are less abundant without directly expending ATP but rely on gradients maintained by ATP-driven pumps.
Step-by-step explanation:
Symports and antiports are mechanisms involved in secondary active transport, which concentrates molecules against their gradient through the use of proton gradients (DpH) and membrane potential differences (ΔY). Symporters transport two or more substances in the same direction simultaneously, while antiporters transport substances in opposite directions.
A well-known example of a symporter is the sodium-glucose symporter, which moves glucose into the cell against its concentration gradient by utilizing the electrochemical gradient of sodium, which moves down its gradient as created by Na+/K+ ATPases.
The sodium-hydrogen antiporter, on the other hand, uses the inward flow of sodium ions to export hydrogen ions out of the cell, thus maintaining the cell's pH. Both processes demonstrate the use of existing gradients to fuel the transport of other substances.