What does the law of conservation of energy state?
energy can be created from nothing.
energy cannot be destroyed.
energy cannot change forms.
the total amount of energy in a system changes continuously.

photosynthesis makes the glucose that is used in cellular respiration to make atp. the glucose is then turned back into carbon dioxide, which is used in photosynthesis. while water is broken down to form oxygen during photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water.