First post on this blog, we’re going to talk about oxygen!
It’s not without some emotion that I’m starting this blog with this article! To start off, I’ve chosen the beginning: oxygen. Oxygen is the reason we breathe. Its use has allowed us to move from an anaerobic to an aerobic system, leading to an evolutionary explosion. From this simple and common molecule, an incredible regulatable system has been set in motion, the human body.
Let’s get familiar with oxygen!
The oxygen molecule, or dioxygen
Oxygen is the third most abundant atom in the universe. Under normal conditions found on Earth, oxygen is found in gaseous form: dioxygen. It is a foundational base of life as most energy sources come from molecules containing oxygen (carbon dioxide used in photosynthesis, sugars, alcohols…) and the bases of DNA contain it. It is also one of the bases of our good metabolic functioning.
Its name was given to it by Lavoisier in 1777, from the Greek « oxus » meaning « acid ». Indeed, its oxidative properties can create a « digestion » of materials. The rusting of iron, for example, occurs between the iron atom, which has an electron « stolen » by the dioxygen molecule.
As it can bind to a lot of things, it also binds to organic matter. It thus forms oxides. Too much oxygen can therefore be toxic! Indeed, an excessive amount of oxygen creates free radicals. These highly reactive free radicals damage cell membranes and organelles! They are responsible for oxidative stress. This is how microbes can be killed with hydrogen peroxide. It’s also one of the causes of aging and the reason why a baby cries when it breathes for the first time! Indeed, the oxygen burns the lungs, which have not yet been accustomed!
Thus, we could not survive in an environment containing 100% dioxygen. Luckily, our atmosphere only contains 21% of it, the rest being nitrogen (78%) and CO2 and other rare gases, making our planet habitable (by us).
Origin of oxygen
By the way, where does this dioxygen come from? Indeed, originally, the Earth’s surface was mainly composed of nitrogen, CO2, and H2O. Oxygen was present but trapped in other forms. Dioxygen therefore appeared 2.7 billion years ago thanks to small microorganisms, the cyanobacteria. These bacteria have the property of performing photosynthesis. In other words, they consume CO2 to feed on Carbon and then release O2. Thus, little by little, dioxygen appeared on Earth.
However, due to its ability to easily bind with just about anything, it didn’t directly enter the atmosphere but attached itself to anything it found, especially iron. It was only after this that it accumulated in the atmosphere, causing a disruption of the primeval ecosystem. Indeed, as mentioned earlier, oxygen is toxic! Thus, this presence of oxygen killed many species of anaerobic microorganisms, giving way to the cyanobacteria, which were then able to multiply, making the atmosphere increasingly oxygenated. This came at the cost of a mass extinction!
This atmosphere full of dioxygen also caused changes in temperature. Indeed, methane, a powerful greenhouse gas, maintained a high temperature on earth. By reacting with oxygen, it was neutralized, cooling the planet. Finally, the O2 allowed the formation of ozone, which then formed the ozone layer protecting from UVs. The Earth could therefore receive more complex inhabitants on its surface.
Oxygen and breathing?
The presence of oxygen thus allowed the appearance of organisms with aerobic respiration. These organisms necessarily consume other organisms to have a source of carbon other than CO2. Indeed, only photosynthetic organisms can use CO2 to convert it into organic matter. These organisms are at the base of the food chain. Others consume them and thanks to the respiration of oxygen get a much higher energy yield, allowing more complex actions such as muscle contraction, for example. Muscle contraction itself allows for a cardiovascular system, for example, and therefore a complexity of organisms in size and functions.
Oxygen allows for better energy efficiency. However, in complex systems, as this molecule is the sine qua non of functioning, its quantity in the body is perfectly controlled. It is thus found in many functions. It is therefore respiration that will give access to these functions that we will discover on this blog as we go along!
See you soon
Yvan