1. Respiration: This is the most fundamental use of oxygen. All living organisms, from humans to plants, need oxygen to breathe and convert food into energy through cellular respiration.

2. Industrial Processes: Oxygen is used in various industrial processes. Some examples include:

* Welding and Cutting: Oxygen is combined with fuel gases like acetylene to produce a very hot flame used for cutting and welding metals.

* Steelmaking: Oxygen is used to remove impurities from molten iron during steel production.

* Chemical Production: Oxygen is a key ingredient in the production of various chemicals, including plastics and pharmaceuticals.

3. Medical Applications: Oxygen therapy is used to treat patients with respiratory conditions like pneumonia, emphysema, and chronic obstructive pulmonary disease (COPD). It's also used in emergency situations like heart attacks and strokes.