Electron transport chain i.e. oxidative phosphorylation at inner mitochondrial membrane. excluding ETC the net production of ATP during glycolysis is 2, while during one Kreb's cycle is 1.
In ETC...
On average less than 1%. It is estimated that volcanoes emit on average 200 million tonnes of CO2 a year. This includes all volcanoes, hot springs and and undersea hydrothermal vents. Humans emit 26...