Oxygen is a fundamental element on Earth, represented by the symbol O and atomic number 8, existing most commonly as a colorless, odorless diatomic gas (O₂). As a highly reactive nonmetal, it readily combines with almost all other elements, making it a potent oxidizing agent that drives countless natural and industrial processes. Oxygen is the most abundant element in Earth’s crust, accounting for approximately 46% of its mass in the form of various oxides and silicates. Although it makes up about 21% of the atmosphere by volume, this reservoir is continuously replenished by photosynthetic life. This gas forms the chemical foundation for nearly all biological and commercial activities that sustain civilization.
Oxygen’s Role in Sustaining Life
For aerobic organisms, the primary biological application of oxygen is serving as the final electron acceptor in cellular respiration, the process that generates metabolic energy. This complex biochemical pathway occurs within the mitochondria, the cell’s energy factories. The goal is to convert the chemical energy stored in nutrients like glucose into a usable form known as adenosine triphosphate (ATP).
The bulk of ATP production takes place in the third stage of respiration, known as oxidative phosphorylation, specifically via the electron transport chain (ETC). High-energy electrons, stripped from nutrient molecules during earlier stages, are passed along a series of protein complexes embedded in the inner mitochondrial membrane. As these electrons move, the energy released is used to pump hydrogen ions (protons) across the membrane, creating a high concentration gradient.
This electrochemical gradient is harnessed by an enzyme called ATP synthase, which uses the flow of protons back into the mitochondrial matrix to power the synthesis of ATP. At the end of this chain, oxygen accepts the “spent” electrons, preventing the pathway from halting. The oxygen molecule combines with these electrons and hydrogen ions to form water, a byproduct that is excreted from the body. Without oxygen to accept these electrons, the ETC cannot operate, and the cell is unable to produce the ATP required to power life functions, leading quickly to cell death.
Therapeutic Applications in Healthcare
Beyond its fundamental role in internal metabolism, oxygen is widely employed in medicine to treat conditions where the body’s natural ability to deliver it is compromised. Supplemental oxygen therapy is the most common external use, providing a higher concentration of oxygen than the 21% found in ambient air to patients experiencing hypoxemia (low blood oxygen levels). This is necessary for individuals suffering from conditions such as Chronic Obstructive Pulmonary Disease (COPD), severe asthma, pneumonia, or late-stage heart failure. Delivery systems range from simple nasal cannulas and face masks to mechanical ventilators that assist breathing.
A distinct and specialized application is Hyperbaric Oxygen Therapy (HBOT), which involves placing a patient in a chamber where they breathe 100% oxygen at air pressures two to three times greater than normal. The increased pressure forces a significantly higher amount of oxygen to dissolve directly into the plasma portion of the blood, dramatically increasing oxygen delivery to tissues. This super-oxygenated blood can reach areas with poor circulation, promoting the growth of new blood vessels and enhancing the white blood cells’ ability to fight infection. HBOT is officially approved for treating decompression sickness (“the bends”), carbon monoxide poisoning, severe non-healing wounds, and certain bone and skin infections.
High-Volume Industrial Processes
The industrial sector consumes immense quantities of oxygen, utilizing its potent oxidizing and combustion-enhancing properties for large-scale manufacturing. The steel industry is the largest commercial consumer globally, where oxygen is central to the Basic Oxygen Furnace (BOF) process. In this method, a high-purity oxygen jet is blown into molten iron to rapidly remove impurities like carbon, silicon, and phosphorus, converting them into gaseous oxides or slag. This refining process is highly efficient, accelerating the production of high-quality steel.
Oxygen is also used in metal fabrication through oxy-fuel welding and cutting, relying on the intense heat generated by combustion. When combined with a fuel gas, typically acetylene, pure oxygen dramatically raises the flame temperature, often exceeding 3,500 degrees Celsius. This high-temperature flame melts and joins metals during welding or rapidly oxidizes and severs steel plates during cutting. Oxygen enrichment also extends to furnaces, such as glass and cement kilns, increasing combustion temperatures to improve efficiency and reduce energy requirements.
Beyond metallurgy, oxygen is a fundamental raw material in the chemical industry, used in oxidation reactions to synthesize important compounds. It is a precursor in the manufacture of ethylene oxide (used to create antifreeze and various plastics) and in the production of nitric acid (employed in fertilizer and explosive manufacturing). The gas is also used in the synthesis of hydrogen peroxide, a common bleaching agent and disinfectant. Oxygen’s role as a powerful reactant allows for the economical synthesis of essential industrial chemicals.
Specialized Uses in Aviation, Space, and Environment
Oxygen is employed to create breathable atmospheres where natural air is unavailable or too thin. In high-altitude aviation, pressurized oxygen systems provide supplemental breathing gas for passengers and crew if cabin pressure is lost above 10,000 feet. Spacecraft and deep-sea diving habitats rely on closed-loop life support systems using stored oxygen to sustain inhabitants. The high-concentration oxygen used requires stringent cleaning protocols to remove organic contaminants, such as oils and greases, which could otherwise react violently and cause a fire or explosion.
Oxygen serves as an accelerator in environmental remediation and cleaning processes. In municipal wastewater treatment, pure oxygen is injected during the secondary treatment stage (the activated sludge process). This stimulates the growth and activity of aerobic bacteria, which efficiently break down organic pollutants. Utilizing pure oxygen, which is 4.8 times more soluble than air oxygen, increases the plant’s treatment capacity and prevents the formation of hydrogen sulfide gas. The same principle is applied in bioremediation projects to clean up contaminated soil and groundwater, where oxygen enhances the metabolic rate of microorganisms that degrade harmful hydrocarbon contaminants.