**Core Concept**
Saturation kinetics in transport processes refers to the phenomenon where the rate of transport of a substance across a cellular membrane reaches a maximum limit as the concentration of the substance increases, beyond which further increases in concentration do not result in a proportional increase in transport rate.

**Why the Correct Answer is Right**
Saturable transport processes, such as facilitated diffusion and active transport, follow saturation kinetics. This is because these processes involve the binding of the substance to specific carrier proteins or channels on the membrane surface, which can become saturated with the substance at high concentrations. In the case of facilitated diffusion, this is typically mediated by carrier proteins or channels, such as glucose transporters or sodium-glucose cotransporters. Active transport, on the other hand, requires energy input and often involves the use of specific transport proteins, such as pumps or exchangers.

**Why Each Wrong Option is Incorrect**
**Option A:** Diffusion is a non-saturable process that follows first-order kinetics. It does not require specific binding sites or energy input and is not limited by membrane surface area or carrier protein availability.

**Option B:** Facilitated diffusion, as mentioned earlier, is a saturable process that follows saturation kinetics.

**Option C:** Active transport is also a saturable process that follows saturation kinetics, as it often involves the use of specific transport proteins that can become saturated with the substance at high concentrations.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that saturation kinetics is a key characteristic of many transport processes in the body, including facilitated diffusion and active transport. Understanding the principles of saturation kinetics can help you predict how different substances will be transported across cellular membranes and how their transport can be influenced by changes in concentration or other factors.

**Correct Answer: A. Diffusion**