Which term is a protein that speeds up chemical reactions?

• A. Catalyst
• B. Enzyme
• C. Hormone
• D. Protein

Answer: (B)

Enzymes are proteins that act as biological catalysts, speeding up chemical reactions by lowering the activation energy required to reach the reaction's transition state. They do this with remarkable specificity: each enzyme has an active site that fits a particular substrate or substrates, often described by the induced-fit model where the enzyme changes shape slightly to snugly bind the substrate. This catalytic power is also regulated by conditions like temperature and pH, and many enzymes need cofactors or coenzymes to work.

Why this term fits best here is that it names a protein with a catalytic role. A catalyst is any substance that increases reaction rate, and it need not be a protein. A hormone is a signaling molecule, not a primary catalyst of chemical reactions. A protein is a broad category that includes enzymes but also many non-catalytic proteins. The one that specifically denotes a protein that speeds up chemical reactions is enzyme.