Oxygen is often seen as a symbol of life, but its role deserves closer examination. Why do so many living beings depend on it for breathing and energy production?
Most organisms, from the smallest to the largest, use oxygen to obtain the energy they need to survive. Donald Canfield, a researcher in Denmark, explains that oxygen is highly efficient for this task because it readily accepts electrons released during respiration.
Living beings like us, called heterotrophs, extract energy by breaking down food. In this process, oxygen plays a crucial role in enabling electron transfer.
Other substances could also accept these electrons, but they are often less practical or hazardous to life. Researchers like David Catling have shown that elements such as fluorine or chlorine would release even more energy, but they are too aggressive to be used by living organisms.
Oxygen is also abundant on Earth. Thanks to plants and algae performing photosynthesis, it is produced in large quantities and is easily found in the air and water. Nitrogen, though highly present in the air, remains too stable to be efficiently used by most living beings.
Oxygen is reactive enough to be useful but not so much as to become dangerous. When used by organisms, it produces water and carbon dioxide—two harmless byproducts. This explains why life has evolved around oxygen.
Another interesting property of oxygen is its ability to accept electrons one by one, releasing energy in a controlled manner without violent reactions. This characteristic, combined with its abundance, makes oxygen an essential element for life on our planet.
How does oxygen help our cells produce energy?
Oxygen plays a key role in cellular respiration, a process that occurs in our cells. It captures electrons at the end of a series of steps that produce ATP, the molecule that supplies energy to cells.
This series of steps takes place in the mitochondria, the cell's "powerhouse." Electrons move from one complex to another, and this flow allows protons to be pumped across the membrane.
Oxygen then accepts the electrons, enabling the formation of water and the continuation of the chain. Without oxygen, everything would stop, and the cell could no longer produce the energy it needs to survive.
Why is there so much oxygen on Earth?
Oxygen is continuously produced by plants, algae, and cyanobacteria, which use sunlight to generate energy and release oxygen.
Unlike other substances that could also accept electrons, such as sulfate or nitrate, oxygen exists as a gas. This makes it very easy to diffuse in the air and water.
Moreover, oxygen is stable enough in its O2 form to accumulate in the atmosphere. Other elements like fluorine or chlorine are either too dangerous or too rare.
Thus, thanks to its constant production and stability, oxygen has become the element of choice for respiration on Earth.