This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ETC, Subject name: Biochemistry
Which of the component of respiratory chain reacts directly with molecular oxygen: 
Select and explain. 
A. Cyt b, B. CoQ, C. Cyt C, D. Cyt aa3
D: Cyt aa3
Answer: D: Cyt aa3 
Explanation: Cyt aa3 is complex IV of ETC, which directly reacts with oxygen. ETC Complex Components Complex I FMN + Fe-S Complex Complex II FAD + Fe - S Complex Complex III Cyt b, Fe-S Complex Complex IV Cyt aa3, Cu