Final answer:
The diagram best models facilitated diffusion, where substances move across the cell membrane through specific proteins without using cellular energy, following the concentration gradient.
Step-by-step explanation:
The diagram provided seems to illustrate a cell process involving substances moving across the cell membrane. This process is similar to what we understand about facilitated diffusion, where molecules or ions pass through the membrane via specific transmembrane proteins. In facilitated diffusion, the transport proteins act as carriers or channels that assist in moving substances from an area of higher concentration to an area of lower concentration without the input of energy (ATP).
This diffusion occurs 'downhill,' meaning it follows the concentration gradient, and is a type of passive transport. The carriers or channels are often selective for certain molecules, and the process is saturable, resembling the kinetics of enzyme action. Importantly, facilitated diffusion is distinct from other forms of passive transport, such as osmosis (specific to water molecules) and simple diffusion (direct crossing of the membrane without aid), and from active processes that require energy input like endocytosis or active transport.