Final answer:
An enzyme is a protein that functions as a biological catalyst, essential for speeding up biochemical reactions within the cell. The correct answer to the question is option a, as enzymes are proteins that are necessary for life and are catalytic in nature. The correct option is A.
Step-by-step explanation:
An enzyme is a substance that plays a crucial role in biochemical reactions within a cell by acting as a biological catalyst. Most enzymes are indeed proteins that facilitate the various chemical processes necessary for life by lowering the activation energies needed for those reactions.
This catalytic feature is vital because it speeds up reactions that would otherwise proceed too slowly to sustain life. Enzymes are designed to be highly specific, meaning each enzyme typically interacts with one particular substrate (or a few closely related ones) to catalyze a single chemical reaction.
Given the options provided in the student's question, the correct answer is: a. An enzyme is a protein. Enzymes are not only proteins but also necessary for life as they catalyze essential reactions in the cell, and they are indeed catalysts. Therefore, the statement that an enzyme is not catalytic is incorrect (option b), and the statement that it is not necessary to sustain life in a cell is also incorrect (option c).