The exchange of oxygen and carbon dioxide takes place in between the lungs and blood. The greater part of oxygen diffuses into the blood and at the same time, carbon dioxide diffuses out. Here the question is where the oxygen would go.
Haemoglobin is a respiratory pigment in RBCs. It is tetrameric conjugated protein. It consists of two parts: haem and globin. Haem is the non-protein part and made up of iron or ferrous (Fe++) containing perphyrins.
Aerobic bacteria use oxygen dissolved in water when breaking down wastes. Scientists can find out how much organic matter the waste water contains by measuring how much oxygen the aerobic bacteria use in breaking it down.
The presence of oxygen in the atmosphere is also harmful. For example, corrosion of metals is caused by oxygen. Slow destruction of metals particularly of iron causes a huge financial loss to the society. Oxygen also causes slow degradation of oils and fats.