Describe electron transport pathway through photosystem I & photosystem II with suitable diagram

Electron transport pathway through PS I & PS II

Fig: Electrons transport pathway through photosystem I & photosystem II

The transfer of electrons from H2O to NADPH is mediated by two separate photochemical reactions through two sets of pigment molecules organized in the form of photosynthetic units, representing the PS I & PS II. Two special kinds of chl a molecules exist in these photo systems. The special chl a molecule in PS II maximally absorbs at 680 nm & is called P680 whereas the special chl a molecule in PS I absorbs at 700 nm & is called P700.

Transfer of light energy to P680 & P700 is greatly facilitated by the existance of antennae attached to the photosystems & each of which comprises about 250-300 chlorophyll molecules bound in special pigment-protein complexes. Photolysis of water takes place in PS II & the electron is transferred via a cytochrome b6/f complex, too complex, to PS I. Here, an electron can gain further energy by absorbing energy from an additional photon & then reach NADP^+ to reduce it to NADPH.