Answer :
Living beings inhale oxygen (O₂) and exhale carbon dioxide (CO₂).
The oxygen that we inhale for our living is present in the air or atmosphere. The oxygen present in the air is required for respiration in human beings.
Oxygen is transported from the air into our body tissues and on the other hand, carbon dioxide is carried away from them. Carbon dioxide maintains the pH of blood. So, oxygen and carbon dioxide the the vital substances for survival of human beings.
Also, plants take in the carbon dioxide that we exhale, for their process of producing oxygen by the process of photosynthesis.
So, there is a balance in the ecosystem for the consumption and release of oxygen and carbon dioxide. This balance promotes the survival of living beings on earth.
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