Primary succession can occur after a

Devastating event

Primary succession usually takes place when after a devastating event , the entire life forms on a particular land gets wiped out and a new land is formed. For example – Eruption of a volcano causes the flowing of lava, which being extremely hot destroys every thing in its path. When the lava coold down a new land would have been formed as it consists of nothing living in that area.  

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.