Air is called the breath of life because it contains various essential gases for human life. It contains gases such as oxygen, carbon dioxide, etc. Oxygen is a gas that is inhaled by living organisms, and this oxygen is used to make ATP energy which is the energy currency of the cell. Carbon dioxide is released from plants as a by-product of respiration which is utilised by plants to carry out photosynthesis. Products of photosynthesis are used in plant growth.