Which of the following statements is true regarding passive transport mechanisms?

Passive transport mechanisms are characterized by their dependence on concentration gradients. This means that substances move from areas of higher concentration to areas of lower concentration without the need for energy input. This process occurs naturally, as it aligns with the principle of seeking equilibrium within the system.

For instance, in osmosis, water moves across a membrane until the concentrations on both sides become equal. Similarly, diffusion allows solutes to spread out in a solution or across a membrane until they reach balance, demonstrating how concentration gradients drive movement in passive transport.

The other aspects of passive transport exclude energy requirements, which are not involved; it does not exclusively utilize carrier proteins, as some forms, like simple diffusion, can occur directly through the lipid bilayer. Furthermore, passive transport is not limited to specific ions; it applies broadly to a range of substances, including non-polar molecules and small polar molecules. Therefore, the focus on concentration gradients accurately reflects a fundamental principle governing passive transport.