Mike and Juan were studying forces and decided to do an experiment. they placed four
equally sized blocks made of different materials on an elevated plastic tray. They watched
each of the blocks move down the tray. their setup is shown in the picture.

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.