g How do cytochromes donate and accept electrons? Each cytochrome has an iron‑containing heme group that accepts electrons and then donates the electrons to a more electronegative substance. Cytochromes donate electrons directly to the energy‑carrier molecules NAD + NAD+ and FAD FAD and accept electrons from less electronegative substances. The cytochromes donate electrons excited by photons to other cytochromes that accept electrons as replacements for lost electrons. Every cytochrome's iron‑containing heme group accepts electrons from oxygen and donates the electrons to the next cytochrome in the chain.

Each cytochrome has an iron-containing heme group that accepts electrons and then donates the electrons to a more electronegative substance
In case of electron transport chain, cytochrome oxidase contains two types of heme group called heme a and heme a3 which catalyzes two coupled reactions: exergonic transfer of electron from cytochrome c to molecular oxygen and endergonic pumping of 2H+ from matrix to intermembrane space
In case of photosynthesis, cytochrome b6f complex act as proton pump and transport protons from stroma to lumen
Cytochrome b6f complex is a transmembrane protein which contains 2 b type cytochrome and 1 c type cytochrome called cytochrome f; cytochrome b6f complex has Fe-S center which involves in single electron transfer reaction