When food is reheated in a microwave oven, bacterial endospores are killed.

A. Are synthesized only when their substrate is available: Inducible enzymes are produced in response to the presence of a substrate or inducer (e.g., the lac operon enzymes are synthesized when lactose is present), conserving cellular resources until needed.

B. Are synthesized continuously by the cell: Constitutive enzymes are synthesized continuously regardless of substrate presence; this statement describes constitutive rather than inducible enzymes.

C. Are only found in prokaryotes: Inducible regulation of enzyme synthesis occurs in both prokaryotes and eukaryotes; it is not exclusive to prokaryotes.

D. Are coded by genes that are always expressed: Genes that are always expressed encode constitutive enzymes; inducible enzyme genes are typically regulated and expressed only under inducing conditions.

A. Koch: Koch’s postulates are criteria for linking a microorganism to a disease and are unrelated to chemical carcinogenicity testing.

B. Ames: The Ames test uses bacteria to detect mutagenic potential of chemicals; because mutagens often correlate with carcinogens, the Ames test is widely used as a screen for carcinogenic potential.

C. Mutation: Mutation is a general term for DNA changes; while mutation assays detect genetic changes, the named specific screening test commonly used for carcinogenic potential is the Ames test.

D. Cancer: “Cancer test” is not a standard name for an assay used to screen chemicals for carcinogenic potential.

E. Iowa: Iowa is a proper noun (a U.S. state) and is not the name of a chemical carcinogenicity assay.