∞ generated and posted on 2016.08.22 ∞
In a linear, multiple-action process, this is the slowest of the necessary actions.
In the reaction, A → B → C, the rate limiting step determines the rate at which A is converted into C and could be either the rate that A is converted into B or the rate at which B is converted into C, whichever is slower.
As an aside, say the way you study for biology class is to first copy over your notes (e.g., as flashcards) and then learn/memorize them. However, while you are great at memorizing these notes, once you have gotten them into some memorizable, i.e., copied form (that is, you are quick study), you nevertheless happen to really hate making the effort to copy over your notes. The result is that a task that could otherwise take relatively little time, studying for an exam once you have already organized the material you need to study from, instead it takes a large amount of time due to procrastination prior to getting started. What here is the rate-limiting step? It is the process of organizing for studying, or simply starting to organize, since once that has happened then the process can proceed to its end point rather rapidly. Nonetheless, the overall process – procrastination followed by organization of material for studying followed by the actual studying process itself – could take quite a large amount to time, and particularly so given a rate-limiting procrastination step.