Phosphorylation

Phosphorylation means adding a phosphate to a molecule. Most importantly, it converts low energy ADP into high energy ATP. This can be done in two ways...

Substrate Level Phosphorylation

In substrate level phosphorylation, an enzyme removes the phosphate from one molecule and attaches it to another molecule - usually ADP.

Substrate is another term for "reactant"
Occurs in cytoplasm during Glycolysis and in mitochondria during Krebs Cycle

Oxidative Phosphorylation (Chemiosmosis)

Oxidative Phosphorylation uses the enzyme ATP Synthase to combine ADP with free phosphate groups.

Energy is provided by a gradient of hydrogen ions created by an Electron Transport Chain
Occurs in Light Reactions of Photosynthesis and Aerobic Respiration