Question

Why do we require oxygen ​

Answer 1

Answer:

for many purposes like breathing , photosynthesis etc

Answer 2

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Our body needs energy for all activities, which is provided by oxidation of food during respiration. During intense physical activities like running, there is larger demand of energy to perform these activities. Hence, more oxygen is required to meet this extra demand of energy.

Short Answer :

We breathe because oxygen is needed to burn the fuel [sugars and fatty acids] in our cells to produce energy.) (Oxygen is brought into the lungs via breathing, where it is transported by red blood cells to the entire body to be used to produce energy