Pheophytin or Pheo is a chlorophyll molecule lacking a central Mg²⁺ ion which serves as the first electron carrier intermediate in the electron transfer pathway of photosystem II in plants and the photosynthetic reaction center RC P870 found in purple bacteria. In both PS II and RC P870, light drives electrons from the reaction center through pheophytin, which then passes the electrons to either a quinone (Q_A) in RC P870 or plastoquinone in PS II. Only chlorophyll of the P680 reaction center in photosystem is capable of transferring an electron to pheophytin. The overall mechanisms, roles, and purposes of the pheophytin molecules in the two transport chains are analogous to each other.. . For more info click here.