This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory chain, Subject name: Biochemistry
[{'content': 'Which complex of ETC reacts directly with O2? \nSelect and explain. \nA. I, B. II, C. III, D. IV', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Complex IV: Cyt-c Oxidase The system functions: * As proton pump * Catalyses transfer of electrons to molecular O2 to form H2O. This is the terminal component of ETC. It catalyses the transfer of electrons from Cyt-c to molecular O2 Cyt-a, Cu++ ions and Cyt-a3.Ref: MN Chatterjea Textbook of Medical Biochemistry, 8th edition, page no: 142', 'role': 'assistant'}]