What term describes a complex chemical that speeds up specific biochemical processes in the body?

The correct term that describes a complex chemical which speeds up specific biochemical processes in the body is "enzyme." Enzymes are biological catalysts that facilitate and expedite various biochemical reactions necessary for maintaining life. They lower the activation energy required for reactions to occur, thus increasing the rate at which these reactions take place without being consumed in the process.

Enzymes are highly specific in their action and work on particular substrates to produce specific products. This specificity is due to their unique three-dimensional structures, which allow them to bind only to certain molecules, thereby catalyzing reactions effectively.

While catalysts are also agents that speed up chemical reactions, the term is more general and can refer to both biological and non-biological substances. In the context of biology, enzymes are the specific type of catalyst that performs these functions in living organisms. The other terms, such as substrate and reagent, do not refer to the complex chemical that speeds up reactions; rather, substrates are the reactants that enzymes act upon, and reagents are substances used in a chemical reaction, often in a laboratory setting. Thus, "enzyme" is the most accurate answer for this question.