Hi, it's not exactly the chemical field we were operating, but a blocking agent is a class of drugs that inhibit some biological processes, whereas the buffer in chemistry is defined as: Chemistry A substance that minimizes change in the acidity of a solution when an acid or base is added to the solution (www.thefreedictionary.com/buffer).
Reaction-diffusion is an equation-based model used to compare for ex. which of two chemicals is diffusing better.
Hope it is OK.
Ciao, Manuela