Answer the following question given this paragraph: 

Aerobic respiration , which takes place in the presence of oxygen, evolved after oxygen was added to Earth’s atmosphere. This type of respiration is useful today because the atmosphere is now 21% oxygen. However, some anaerobic organisms that evolved before the atmosphere contained oxygen have survived to the present. Therefore, anaerobic respiration , which takes place without oxygen, must also have advantages.


Q: Anaerobic respiration takes place without what?


A:
oxygen