Human Exhaust – CO2

We breath in oxygen and breath out carbon dioxide, where does the carbon come from?

Answers provided by Etheria Randomia

From our footprints, of course. ~ Jim Dewar, North Gosford

The carbon dioxide breathed out is a by-product of the process of cell respiration, as is water. In this process, energy is produced in the mitochondria of cells. This energy is our physical “life force”. Both oxygen and glucose are required for this. Glucose contains carbon. That’s where the carbon in carbon dioxide comes from. Glucose plus oxygen produces carbon dioxide, water and energy. When this process stops, the cell dies. ~ John Blackhawk, Umina Beach

The food and drink we eat can be broken into carbon compounds, one of the most simple being glucose (C6H12O6). When that reacts with oxygen (O2) in the cells, it produces carbon dioxide (CO2) and water (H2O). C6H12O6 plus 6O2 gives 6CO2 plus 6H2O plus energy. We use the energy and the carbon dioxide is breathed out as gas. ~ Howard Clark, Ryde

Like other things in life, breathing isn’t that simple. What we breathe in is far from pure oxygen, but roughly by volume 78 per cent nitrogen, 21 per cent oxygen, 0.965 per cent argon and 0.04 per cent carbon dioxide (plus some helium, water and other gases). The permanent gases in air we exhale are roughly 78 per cent nitrogen, 15 to 18 per cent oxygen (we retain only a small amount), 4 to 5 per cent carbon dioxide and 0.96 per cent argon, the CO2 being of course used by plants during photosynthesis. ~ John Moir, Mollymook

Carbs. ~ Matt Wormald, Neutral Bay

Trees and plants give off carbon dioxide when they breathe, and when they die and rot. We breathe in oxygen and some of this carbon dioxide. When we exhale, we breathe out less oxygen but more carbon dioxide than we inhale. ~ Paul Roberts, Lake Cathie

The carbon we breathe out as carbon dioxide comes from the carbon in the food we eat. The carbohydrates, fat and proteins we consume and digest are eventually converted by a number of different biochemical pathways in the body to glucose (C6H12O6). The glucose molecule is then combined with oxygen in the cells of the body in a chemical reaction called “cellular oxidation”. This chemical reaction is exothermic, that is, it produces the chemical energy that is needed to drive all the other chemical reactions and functions of a cell. The end products of oxidation of glucose are carbon dioxide and water. The carbon dioxide is dissolved in the blood, carried to the lungs by the circulation, and breathed out. ~ Dr John Frith, Paddington

Every living cell of our body carries out the energy-releasing process of respiration, where glucose (a simple sugar) is slowly “burnt” (oxidised) to give off carbon dioxide (excreted through the lungs) and water. Glucose is a carbohydrate and is also a digestive breakdown product of starch (in potatoes, etc). Glucose is made in the first place in the leaves of plants from solar energy – the process of photosynthesis is the reverse of respiration. ~ Chris Hasemore, Bangalee

Carbon exists in the earth’s atmosphere primarily as the gas carbon dioxide. This makes up 0.04 per cent of the permanent gases we breathe in, being converted to about 4.5 per cent of what we exhale. Only 21 per cent of what we inhale is oxygen and of this, 15-18 per cent is exhaled, the body retaining (generally) enough for its needs. ~ John Moir, Mollymook