What is the process of transporting materials across a plasma membrane without the use of energy called?

The process of transporting materials across a plasma membrane without the use of energy is called passive transport. This mechanism relies on the natural movement of molecules from an area of higher concentration to an area of lower concentration, a process driven by the concentration gradient. Passive transport can occur through simple diffusion, where small nonpolar molecules pass directly through the lipid bilayer, or facilitated diffusion, where larger or polar molecules move through specific transport proteins in the membrane.

The key characteristic of passive transport is that it does not require cellular energy (ATP) to occur, as it harnesses the inherent kinetic energy of the molecules involved. This is fundamental to various biological processes, allowing cells to maintain homeostasis and efficiently exchange substances.

Active transport, on the other hand, does require energy to move substances against their concentration gradient. Endocytosis is a process that involves the engulfing of materials into the cell using energy, which is distinctly different from passive mechanisms.