The lock-and-key mechanism refers to the complementary shapes of an enzyme and a substrate. the attractive forces between an enzyme and a substrate. the ability of an enzyme to lower the activation energy of a reaction. the ability of an enzyme to “unlock” the products of a reaction.

the complementary shapes of an enzyme and a substrate.

Explanation:

Enzymes are complex macromolecules which catalyse various metabolic processes in the living organism to keep them alive. Enzymes are highly specific in nature. They catalyse specific substrates involved in the reactions. Each enzyme has an active site where the specific substrate binds to the active site forming the enzyme-substrate complex. The action of an enzyme with the substrate is like working of ‘lock and key’.  According to the lock and key hypothesis, the active site of an enzyme has a very unique shape and it is only complementary to a specific substrate molecule.

a. decomposes use carbon from dead organisms as fuel for cellular respiration, returning carbon dioxide back into the atmosphere.