Final answer:
The PTS system is more efficient for sugar import into bacterial cells because it chemically modifies the sugar during transport, eliminating the need to move it against a concentration gradient and making the process energy neutral. In contrast, facilitated transport is slower, and symporters, though active, are less efficient as they rely on energy from ion gradients, which indirectly use ATP.
Step-by-step explanation:
The Phosphotransferase System (PTS) import of sugars is more efficient than import via other transporters due to its unique mechanism of group translocation. As a molecule, such as glucose, is transported into the bacterial cell, it is simultaneously chemically modified by the addition of a phosphate group.
This process effectively bypasses the need to move glucose against an unfavorable concentration gradient, as the modified glucose does not readily diffuse out of the cell.
Additionally, because the phosphorylation of sugars is a necessary step in sugar metabolism, this transport mechanism can be considered energy neutral, providing a metabolic efficiency not seen with facilitated transport, symporters, or other carrier proteins.
In contrast, facilitated transport via carrier proteins is not an active process and hence, is slower and dependent on the concentration gradients of the transported molecules.
Symporters, while capable of moving substances against their concentration gradient, rely on the co-transport of another ion such as sodium and are less efficient than PTS in terms of energy expenditure as it indirectly uses the energy from ion gradients established by ATP-driven pumps like the sodium-potassium pump.