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?
1) Cells are less efficient at energy metabolism than reactions that are optimized in a test tube.
2) The amount of heat released by a reaction has nothing to do with the free energy change of the reaction.
3) In the cell, the hydrolysis of ATP is coupled to other endergonic reactions.
4) In cells, ATP is hydrolyzed to ADP and Pi, but in the test tube it is hydrolyzed to carbon dioxide and water.
5) Cells have the ability to store heat; this cannot happen in a test tube.