Oxygen The human biological process depend on oxygen. Can you try to live without it through few minutes and I will promise you don't live more :D. The series question is why we need to oxygen? Why we think it is the secret of life ? I actually don't give science lecture or biological tutorial. I hear to say The oxygen of life is knowledge. You are learning . You are earning new level . You are living. Ignoring means the life without oxygen.

Immunity Immunity means the production. The countries use army to product their borders. Police system is to face internally problems. We can ask that how many enemies have the country the ability to eliminate them ? 10000 or 100000 or 1 M You can think imagine the human immune system has ability to eliminate 10^9 to 10^11 types of enemies (antigens or pathogens) I believe the best and strongest immunity system is in the human body.