Breathing, or respiration, is a continuous biological process that sustains life. This action involves drawing in a mixture of gases from the surrounding atmosphere into the lungs. The body takes in atmospheric air and selectively processes certain components to fuel its internal machinery. Understanding the composition of the air we breathe in and the air we release reveals the precise chemical exchange necessary for survival.
Composition of Atmospheric Air
The air we draw into our lungs is a consistent blend of several gases. By volume, the atmosphere is composed of approximately 78% nitrogen. Oxygen is the second most common component, accounting for about 21% of the total volume of inhaled air.
The remaining 1% is made up of trace gases, primarily the inert gas argon, which constitutes about 0.93%. Carbon dioxide is present only in very small amounts in the air we inhale, around 0.04%. This composition represents the raw material the respiratory system takes in.
How the Body Uses Oxygen
The primary purpose of respiration is to acquire oxygen for the body’s metabolic processes. Once inhaled air reaches the lungs, it enters millions of tiny air sacs called alveoli, which are surrounded by a dense network of capillaries. This is the site of gas exchange, where oxygen moves from the high-concentration area in the alveoli across a thin membrane into the bloodstream.
Oxygen molecules quickly bind to hemoglobin, a specialized protein contained within red blood cells, which efficiently transports the gas throughout the circulatory system. The oxygen-rich blood is then pumped to tissues and cells across the body where it is needed for energy production. This energy is generated through a process known as aerobic cellular respiration, which primarily occurs within the mitochondria of cells.
Oxygen acts as the final electron acceptor in the electron transport chain, driving the production of adenosine triphosphate (ATP), the cell’s primary energy currency. This reaction uses oxygen and nutrient molecules, like glucose, to create ATP, producing water and carbon dioxide as waste products. The carbon dioxide is then picked up by the blood and carried back toward the lungs to be expelled.
The Gases We Release
The air that is ultimately exhaled is chemically distinct from the air that was originally inhaled, reflecting the changes made during internal gas exchange. The most significant shifts occur in the concentration of oxygen and carbon dioxide. Exhaled air contains a reduced amount of oxygen, dropping from 21% down to 16% to 17%.
Conversely, the concentration of carbon dioxide increases, rising from the inhaled trace amount of 0.04% to 4% to 5% in the air we breathe out. This four to five percent increase is the accumulated waste product from cellular energy production across the body. Nitrogen, which makes up the bulk of inhaled air, remains unchanged, staying at 78%. The body does not utilize nitrogen for metabolic processes, so it is simply carried in and out of the lungs with minimal absorption.