What is the structure and function of "electron transport chain" in chloroplast and mitochondria?
The structure is a series of proteins embedded in a membrane that pump hydrogen ions in one direction to create a concentration gradient - the function is generate ATP.
The electron transport proteins accept high energy electrons from the electron carriers NADPH (in photosynthesis) and NADH & FADH2 (in cellular respiration), and through the action of transporting them from one to the other in a series of electron exchanges, small units of energy are extracted and used to pump hydrogen ions.
I cell respiration they are pumped from the matrix into the intermembrane space of the mitochondria - in photosynthesis they are pumped from the stroma into the lumen of the thylakoids.
In both cases, the high concentration of hydrogen ions can't cross the membrane (due to their charge), and place a great deal of osmotic pressure on the membrane. This pressure drives the hydrogen ions from [high] --> [low] through the enzyme ATP Synthase - using this energy to produce ATP molecules.