Achemical reaction is an interaction that always causes what

A chemical interaction is compelled by electrostatic forces which can occur both in vitro (studies are done outside living organisms), and in vivo  (scientists conduct their studies with the use of whole living organisms).  In simpler terms a chemical reaction is a change that occurs when two or more substances combine to form a new substance.

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.