Why is oxygen an important kind of gas?

Answer 1

Oxygen is important to us because almost all forms of life on earth use oxygen in cellular respiration. Cellular respiration is a reaction that takes glucose (a compound derived from food, originally constructed by plants in photosyntesis) and oxygen and creates water, carbon dioxide and releases a significant amount of energy. That energy is what allows the cell to do whatever it does. If those cells stop working, so does the thing they collectively are, be that thing a person, another type of animal, a plant, a fungus, protist, or bacteria.

Oxygen is actually produced as a waste byproduct in some reactions. Many of the bacteria that do not consume oxygen are actually oxygen producers. In the last billion or so years, plants have largely replaced bacteria as oxygen producers, since more oxygen is released during photosynthesis than is used by the plant's cellular respiration (this also results in a net reduction in carbon dioxide by the plant, since it consumes more carbon dioxide in photosynthesis than it produces in cellular respiration.)