Which two biological processes are most directly dependent on the availability of air?

The two biological processes most directly dependent on the availability of air are respiration and photosynthesis. Respiration, carried out by animals and many microorganisms, requires oxygen from the air to produce energy by metabolizing food. Photosynthesis, conducted by plants and certain bacteria, relies on carbon dioxide from the air to convert light energy into chemical energy, ultimately producing oxygen as a byproduct.