If the work output of a machine equals the nonzero work input, then is equal to 0.

You've built quite a convoluted question there, Thelo.

If you wrote what you mean and I read it correctly, then the phrase
in the blank is "... the loss of energy to friction in the machine ...".

The answer is water molecules are split.cellular respiration and photosynthesis are complement  reactions to each other. these are reverse reactions. in cellular respiration glucose and oxygen yield water and carbon dioxide. so, when respiration begins,  glucose molecules are split. in the opposite reaction - in photosynthesis, carbon dioxide and water yield glucose and oxygen. thus,  when respiration begins, water molecules are split.