While all the living organisms (including human beings) are carbon-based forms, carbon is not the only element we need to sustain our bodies. The complexity of a cell is beyond the mechanisms of what humans are used to dealing with. Although carbon makes up everything in our bodies, from the proteins present in our hair to our complex DNA, it does so in conjugation with other elements – like HYDROGEN (H), OXYGEN (O), and NITROGEN (N). Those CELL ORGANELLES (the “organs” of the cell) which primarily compose of C, H, and O and form HYDROCARBONS but there are other cellular products that possess the nitrogen atom as well – in particular, amino acids and nucleic acids.
Various other elements are highly crucial for our survival as well – such as magnesium (Mg), zinc (Zn), and iron (Fe). Since our cells require this platoon of elements to make us what we are, they are complex structures. At the inception of earth, the atmosphere was of the REDUCING kind (more of hydrogen than oxygen). One of the first organisms to be present on the earth were the CYANOBACTERIA, which made the atmosphere OXIDATIVE through their respiratory processes. Many biologists attribute the presence of oxygen to be the reason for the evolution of complex organisms, which have evolved into the humans and the other animals that walk the earth today.
Still, it is commonly said that “Humans cannot survive without oxygen” despite the necessity of the other elements. From this statement, it is deduced that the importance of oxygen is more than that of the other elements. So, can humans survive without oxygen? The answer is no.
What does oxygen do in the body?
The sources of oxygen coming into our body are plenty – food, atmospheric oxygen, and water.
- Water is made up of two molecules of hydrogen and one molecule of oxygen, giving it the denotation of H2O.
- Oxygen makes up 21% of the atmosphere. We take in this atmospheric oxygen through our noses to enable a process called RESPIRATION.
- The foods we consume contain a plethora of biomolecules (like carbohydrates and proteins) which are made up of hydrocarbons. Thus, oxygen is also present in food.
Humans and many other living beings (e.g., other animals, even various types of microorganisms) require oxygen to carry out cellular functions and maintain the integrity of their bodies. Organisms that require oxygen are called AEROBES. Those who do not require oxygen in their bodies or those who would not survive in an oxidative environment are called ANAEROBES – Clostridium tetani, the causative agent of TETANUS is an obligate anaerobe; the organism will die in presence of oxygen.
The bodies of anaerobes and aerobes differ in function and reaction to the presence of oxygen. Since humans are aerobes, we will restrict this discussion to the requirement and utilization of oxygen in the body and forego the mechanisms by which anaerobes survive. Oxygen plays numerous roles in the body – rather, oxygen’s contribution to one process causes a cascade of reactions to be possible; the culmination of all these processes helps us stay alive.
- Cellular respiration
In a gist, cellular respiration can be described as a series of biochemical reactions carried out to convert carbohydrates (from food) into simpler products, namely CO2. CO2 that is generated is a waste product that is exhaled via the nose during respiration.
These sets of reactions occur under a regulated oxidative environment, where oxygen is present in the form of water and is utilized by the enzymes catalyzing the reactions as well as is directly involved in the electron transfer.
2. Energy production
The direct consequence of cellular respiration is the production of energy. ADENOSINE TRIPHOSPHATE or ATP is called the “energy currency” of the body. It is a compound of nitrogenous base adenosine in conjugation with three phosphate molecules. The breakdown of each bond of the compound imparts a specific amount of energy wherever it is required. One cannot run, walk, or perform any task in the absence of ATP.
As oxygen-driver cellular respiration proceeds, monitored formation and breakdown of ATP ensue. There is always a net gain of ATP at the end of these reactions, which migrated to other locations in the cell to drive reactions that require energy, called ACTIVE PROCESSES. Since the role of oxygen in the formation of ATP is crucial, scientists also prefer to state that a consequence of cellular respiration is “the conversion of oxygen to the energy currency of the body, ATP.”
3. Breakdown of other biomolecules
Foods are not only composed of carbohydrates but also fats and proteins. While carbohydrates (primarily glucose) are the preferred sources of energy, fats can also engage in energy production by breaking down to its constituents. Oxygen also plays a role in the breakdown of fats by providing an oxidative environment and for the enzymes to function.
4. Cranial function
The brain is often referred to as the CPU of the body. It is the organ that enables us to perform every action – from moving our finger to solving the trickiest puzzles. The brain is a structure so complex that scientists believe we have barely scratched the surface to comprehend it. A structure so complex is highly sensitive to the presence of one element – oxygen.
Under normal circumstances, the haem group of the blood (HAEMOGLOBIN) binds oxygen and distributes it to each organ. Similarly, the brain is supplied with its share of oxygen via the blood. Adequate oxygen facilitates the error-free performance of the brain and smooth signal transmission by the neurons. The dependency of the brain on oxygen has sensitized it to oxygen deprivation; oxygen deprivation for a certain amount of time (≥ five minutes) manifests as a resulting BRAIN DEATH.
Can any other system replace oxygen in the body?
The human body has evolved to perform one of the functions of oxygen even in the absence of oxygen. This series of biochemical reactions were not designed to help a human survive in absence of oxygen (which is not possible since the brain would be long dead) but to work in conditions where oxygen is in low concentrations – such as during physical exhaustion. The process of cellular respiration has been described above, which requires oxygen to convert carbohydrates into CO2. However, there is a “back-up” process to cellular respiration where oxygen is low – ANAEROBIC RESPIRATION in muscles.
People regularly engaged in physical training are familiar with the feeling of the sore muscle. Muscle pain following exercise is an indication of anaerobic respiration occurring in the muscles. Exercise increases the metabolism of the body and the body burns off oxygen at a higher rate than normal. Thus, at some point in time, the cells (muscle cells in particular) run out of oxygen and utilize an anaerobic pathway to digest glucose. The end-product of aerobic digestion of glucose is a compound called PYRUVIC ACID, which is further broken down into CO2. In anaerobic digestion, the end-product is LACTIC ACID (which causes the soreness in the muscles), which is also digested further to form CO2. As mentioned before, this reaction occurs when the concentration of oxygen reaching the muscle cells is low, not when oxygen is absent.
In the absence of oxygen, all the bodily functions will halt and when brain death will occur, these functions will cease to exist. The importance of oxygen is unlike the other elements – carbon and hydrogen are mostly found in conjugation while the other elements are supplemented through food and aid the functions of enzymes by acting as CO-FACTORS. The sources of oxygen are easily accessible to us to ensure that oxygen deprivation is never encountered. Oxygen not only sustains a living body but is also a constituent of our surroundings – natural or man-made. Hence, it is safe to say that not just humans, but the entire ecosystem and perhaps even the earth will be unable to sustain themselves without a constant supply of oxygen.