Questions: Which of the following is true of metabolic reactions? A. They are all catalyzed by enzymes B. They all release energy C. Organisms use the same reactions to maintain life D. They always use or produce ATP

The answer is A: They are all catalyzed by enzymes.

Explanation for each option:

A. They are all catalyzed by enzymes - This is correct. Enzymes are biological catalysts that speed up metabolic reactions in living organisms. Almost all metabolic reactions require enzymes to proceed at a rate sufficient for life.

B. They all release energy - This is incorrect. Metabolic reactions can be either exergonic (releasing energy) or endergonic (requiring energy input). Not all metabolic reactions release energy; some require energy to proceed.

C. Organisms use the same reactions to maintain life - This is incorrect. While many metabolic pathways are conserved across different organisms, there is significant diversity in metabolic reactions due to different environmental adaptations and evolutionary histories.

D. They always use or produce ATP - This is incorrect. While ATP is a common energy currency in cells, not all metabolic reactions directly use or produce ATP. Some reactions may involve other energy carriers or intermediates.

In summary, the correct statement about metabolic reactions is that they are all catalyzed by enzymes.