a. In puple bacteria P870 is present. External electron donors are hydrogen, hydrogen sulphide, organic molecules like succinate, malate etc. are there. First electron is withdrawn from Pheophytin. b. In Green sulfur bacteria source of electron is H2S, when No NADP+ is reduced. Solution a. In puple bacteria P870 is present. External electron donors are hydrogen, hydrogen sulphide, organic molecules like succinate, malate etc. are there. First electron is withdrawn from Pheophytin. b. In Green sulfur bacteria source of electron is H2S, when No NADP+ is reduced..