When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell. Which of the following best explains these observations?

• A. Cells are less efficient at energy metabolism than reactions that are optimized in a test tube.
• B. The amount of heat released by a reaction has nothing to do with the free energy change of the reaction.
• C. In cells, ATP is hydrolyzed to ADP and P_i, but in the test tube it is hydrolyzed to carbon dioxide and water.
• D. Cells have the ability to store heat; this cannot happen in a test tube.
• E. In the cell, the hydrolysis of ATP is coupled to other endergonic reactions.