This is a cellular respiration question, related to biology.
Some processes in our bodies require the use oxygen, others do not.
In this case, the conversion of pyruvic acid to acetyl co-enzyme A and the production of water in the electron transport chain do require oxygen. 
If oxygen was not present for pyruvate, it would turn into lactic acid via fermentation. Water in the ETC is formed in the process when NADH and FADH2 are converted to molecular oxygen due to the electron transporters. The protons are then pumped and oxygen is reduced to form H2O. 
 
        
                    
             
        
        
        
From the contour line that is a combination of two line segments that connect but do not intersect, 500 and 750 represent elevation on the topographic map. There are 5 contour lines in between the given elevations 500 and 750, therefore, the contour interval is 50. Since the peak of the mountain is 2 contour lines from 750, the elevation of the mountain is 850. Hence, the answer is 871 meters.
        
                    
             
        
        
        
Answer:
The answer is Physical. Physical immunity occurs when a person immune system responds to antigen. 
Explanation: