Question

Briefly describe the process by which (a) oxygen from atmosphere is used up
(b) how​​​​how oxygen is returned to atmosphere

Answer 1

a) human beings take in that oxygen which we used to break carbohydrates down into energy in a process called respiration.So oxygen from atmosphere is used up by the process called respiration

b)photosynthesis is the process by which plants make their food in the presence of CO₂ and sunlight, thus releases oxygen in the atmosphere.