Question

which characteristics of enzymes are accurate? select all that apply.
enzymes lower the activation energy of chemical reactions.
enzymes can only use specific molecules as substrates.
enzymes increase the free energy of chemical reactions.
enzymes require an energy input to catalyze chemical reactions.
enzymes operate efficiently across all temperature and ph conditions.

Explanation:

• Enzymes act as catalysts. Catalysts lower the activation energy of chemical reactions, so "Enzymes lower the activation energy of chemical reactions" is correct.
• Enzymes have a specific active - site structure. This structure allows them to bind only to specific substrates (molecules on which they act), so "Enzymes can only use specific molecules as substrates" is correct.
• Enzymes do not change the free - energy change ($\Delta G$) of a reaction. They only speed up the reaction by lowering the activation energy. So "Enzymes increase the free energy of chemical reactions" is incorrect.
• Enzymes themselves do not require an energy input to catalyze reactions. The activation energy of the reaction (which is lowered by the enzyme) is the energy barrier for the reaction, not an energy input for the enzyme. So "Enzymes require an energy input to catalyze chemical reactions" is incorrect.
• Enzymes have optimal temperature and pH conditions. Outside of these conditions (e.g., very high temperatures can denature enzymes, extreme pH can disrupt enzyme structure), their efficiency is reduced. So "Enzymes operate efficiently across all temperature and pH conditions" is incorrect.

Answer:

Enzymes lower the activation energy of chemical reactions, Enzymes can only use specific molecules as substrates.