Question

in metabolic pathways, the product of a reaction can become the ____________ for the next reaction.
product
substrate
by product
protein

Explanation:

In metabolic pathways, reactions are sequential. The product of one reaction often serves as the starting - material (substrate) for the next reaction. A product is the result of a reaction and not typically the same as the starting - material for the next reaction. A by - product is an additional, often unwanted product of a reaction. A protein can be an enzyme that catalyzes reactions but not the reactant in the sense described here.

Answer:

B. substrate