Give scientific reasons.

Oxygen is necessary for complete oxidation of glucose.

All living organism requires energy to live and to perform any useful functions. This energy they get from food they eat. Energy is released when food contains nutrients, let’s say carbohydrate (glucose). Energy released in the cells when oxidation of glucose occurs which means the carbohydrates which we eat converted into simpler substances with the help of oxygen. For complete oxidation of glucose(i.e the breakdown into simpler substances) oxygen is necessary.

6O₂+C₆H₁₂O6CO₂+6H₂O+38ATP