Final answer:
Enzymes are proteins that catalyze chemical reactions in cells by facilitating the lowering of activation energy required for reactions. They speed up reactions without altering the overall free energy change and are highly selective towards their substrates.
Step-by-step explanation:
Enzymes are proteins that help increase the rate of chemical reactions inside cells. These enzymes operate by facilitating the activation energy needed for a reaction to begin. The correct answer to the student's question is: d) Proteins, facilitating.
Enzymes are biological catalysts that significantly speed up the rate of virtually all of the chemical reactions that take place within cells. They do this by providing an environment in which the reactants can be brought together in an optimal orientation, which lowers the requisite energy for a reaction to proceed, known as the activation energy. Unlike other catalysts, enzymes are highly selective, typically interacting with only one type of substrate — the material or molecule upon which an enzyme acts.
It is essential to note that while enzymes decrease the activation energy, they do not alter the overall free energy change (ΔG) for the reaction. They simply allow the reaction to proceed at a much faster rate than it would without the presence of the enzyme. By binding to substrates at the active site, enzymes facilitate the formation of transition states and lower the energy barriers that must be overcome for reactions to occur.