Question

What is the difference between photophosphorylation and oxidative phosphorylation?

Answer 1

Both of these processes generate ATP via Electron transport chain but during different phenomena in plants. Chemiosmotic hypothesis explains the synthesis of ATP in chloroplasts as well as in the mitochondria. Proton motive force or PMF required for phosphorylation is obtained with the use of energy of oxidation-reduction.

Complete answer:
Electron transport chain is a series of electron carriers over which electrons pass in a downhill journey releasing energy at every step that is used in generating an electrochemical proton gradient which helps in synthesizing ATP.
The process of reduction of NADP and $NADPH^+$ a proton may be denoted as electron transport system (ETS) in photosynthesis while the process of formation of ATP from ADP and an inorganic phosphate utilizing light energy is called photophosphorylation. Based on the path of electrons, it can be classified as non-cyclic and cyclic photophosphorylation. In cyclic photophosphorylation, photolysis of water does not occur and hence, no oxygen is evolved. It occurs mostly in the stroma lamellae membrane. On the other hand, liberation of oxygen by photolysis of water occurs in non-cyclic photophosphorylation. It occurs in granal thylakoids.
Oxidative phosphorylation is a process of generation of ATP during respiration in plants. It involves the passage of electrons on to oxygen resulting in the formation of water. This process occurs in the inner mitochondrial membrane. Electrons from NADH are oxidised by an NADH dehydrogenase or Complex I. Electrons are then transferred to ubiquinone which also receives reducing equivalents from $FADH_2$ or Complex II. The electrons are then transferred to cytochrome c via cytochrome bc1 complex or Complex III. Then the electrons are transferred to Complex IV that consists of cytochrome a and a3 and two copper centers. Oxygen acts as a terminal electron acceptor. It becomes reactive and combines with protons to form metabolic water.

Note:
Redox potential is the measure of the tendency of a chemical species to acquire electrons and thereby get reduced. It is measured in Volts or MilliVolts. Photorespiration is a process which involves loss of fixed carbon as Carbon dioxide in plants in the presence of light. It occurs in chloroplasts and it does not generate any ATP or NADPH and is rather a wasteful process.