What does multicelluraity only occur in

multicellularity occurs by cells separating and then rejoining

multicellularity occurs as a consequence of cells

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.

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.