How do organisms generate ATP?

Plants - harness light energy into chemical energy of ATP (photosynthesis) Eukaryotes- extract high energy electrons from fuels (mostly sugars) to synthesise ATP. This process is called oxidative phosphorylation and occurs in three key steps: 1)electrons flow through the mitochondrial electron transport chain to reduce oxygen, resulting in formation of a water molecule 2) the electron flow results in pumping of protons across the inner mitochondrial membrane, from matrix to the intermembrane space, creating a proton motive force or gradient  3) protons flow black into the matrix through ATP synthase, resulting in synthesis of ATP (chemiosmosis)