We can only live for a few minutes without oxygen, but the amount of oxygen our body needs is related to what we’re doing. The more active we are, the more oxygen our body needs. The respiratory centre in the brain-stem monitors the levels of oxygen, carbon dioxide (CO2), and hydrogen ions (H+), while also receiving data on muscular activity. It analyses this information and sends out orders to the lungs, telling them to breathe in and out at a rate and depth that allows the body to keep doing what it needs to do to survive.

To stay active, our body needs to use more oxygen to give our muscles the energy they require to overcome forces such as inertia, gravity, friction, and wind resistance. All cells need oxygen to live and it is freely available in the air around us, but how does oxygen reach our body’s cells?

The lungs consist of large airways called bronchi and smaller ones called bronchioles. They are lined with a mucous membrane that warms and humidifies the air as it moves down into the hundreds of millions of alveoli, deep inside the lung. Each alveolus is surrounded by hundreds of small blood vessels called capillaries.

It is here that the oxygen molecules undergo a change once they are inside the body. The gas molecules, which circulate in the air, dissolve into a solution within the blood’s plasma located within the capillaries of the alveoli. Once those dissolved oxygen molecules are in the solution of the blood, 98% of the dissolved oxygen is taken-up by red blood cells, which are passing by. The other 2% of the dissolved oxygen remains in the physical solution.

Red cells are great vehicles for transporting the dissolved oxygen. That’s because red blood cells contain a special oxygen-binding protein known as ‘haemoglobin’. Each haemoglobin molecule contains something else which is important for transporting oxygen: four molecules of ‘heme,’ which is an iron-containing pigment capable of binding oxygen loosely and reversibly.

When haemoglobin is fully saturated with oxygen, its colour is bright red, and it’s called ‘oxyhaemoglobin’. When haemoglobin is not fully saturated with oxygen, its colour is purplish-blue, and it’s called ‘deoxy-haemoglobin’. It is the heme in haemoglobin which makes it possible for red blood cells, which are passing by, to pick-up oxygen dissolved in the blood and then transport it. Combined with haemoglobin, the dissolved oxygen is then released back into the blood as oxygen in the solution.

Now it is ready for delivery to various cells throughout the body.

When oxygenated blood reaches muscle cells, the bond between oxygen and haemoglobin molecules loosens.

When the red blood cells pass single file through the tiny capillaries that surround muscle cells, oxygen molecules are released from haemoglobin and diffuse into the muscle cells. The carbon dioxide produced by the muscle cells diffuses into the blood-stream not as carbon dioxide but as bicarbonate ions that are converted back into carbon dioxide in the lungs, where it is exhaled.

So, here is the crucial question: if the body cannot survive for longer than 5 minutes without oxygen, how possibly could a human being survive if this system of oxygen transfer is taking millions of years to evolve? The answer is that the body could not survive. It needs a mechanism to bring air into the body, a mechanism to dissolve the gas into a chemical, a mechanism to transport it around the body and a mechanism to remove the waste. If all of this is not working within 5 minutes, then life as we know it would not exist.

The scriptural record is very clear – God breathed into man the breath of life and man became a living creature – instantly and miraculously.