question: How are we not wasting oxygen when we breathe out carbon dioxide?
comment: We take in oxygen because when it chemically joins with something, it releases energy. We then use that energy to live. Once it has done that, when it has joined with carbon to make carbon dioxide, its job is done, The energy available has been released. You see, it isn't the oxygen we need. It is the chemical energy available in having oxygen and carbon/hydrogen as separate things - the carbon/hydrogen loosely bound into carbohydrates like sugar. It is a bit like how a hydro-electric plant doesn't 'waste water' when the water that flows out of the tail race at the bottom of the dam. The plant didn't want water - it wanted the energy in that water being up there at the top. Now the generator has been spun, the energy caught from allowing the water to fall to the bottom, the job is done and the low energy water released.
passages: It is only as a result of accurately maintaining the composition of the 3 liters of alveolar air that with each breath some carbon dioxide is discharged into the atmosphere and some oxygen is taken up from the outside air. If more carbon dioxide than usual has been lost by a short period of hyperventilation, respiration will be slowed down or halted until the alveolar partial pressure of carbon dioxide has returned to 5.3 kPa (40 mmHg). It is therefore strictly speaking untrue that the primary function of the respiratory system is to rid the body of carbon dioxide “waste”. The carbon dioxide that is breathed out with each breath could probably be more correctly be seen as a byproduct of the body’s extracellular fluid carbon dioxide and pH homeostats
   It is only as a result of accurately maintaining the composition of the 3 liters alveolar air that with each breath some carbon dioxide is discharged into the atmosphere and some oxygen is taken up from the outside air. If more carbon dioxide than usual has been lost by a short period of hyperventilation, respiration will be slowed down or halted until the alveolar formula_3 has returned to 5.3 kPa (40 mmHg). It is therefore strictly speaking untrue that the primary function of the respiratory system is to rid the body of carbon dioxide “waste”. In fact the total concentration of carbon dioxide in arterial blood is about 26 mM (or 58 ml per 100 ml), compared to the concentration of oxygen in saturated arterial blood of about 9 mM (or 20 ml per 100 ml blood). This large concentration of carbon dioxide plays a pivotal role in the determination and maintenance of the pH of the extracellular fluids. The carbon dioxide that is breathed out with each breath could probably be more correctly be seen as a byproduct of the body’s extracellular fluid carbon dioxide and pH homeostats
   Anthropogenic carbon emissions exceed the amount that can be taken up or balanced out by natural sinks. As a result, carbon dioxide has gradually accumulated in the atmosphere, and , its concentration is almost 48% above pre-industrial levels. Various techniques have been proposed for removing excess carbon dioxide from the atmosphere in carbon dioxide sinks. Currently about half of the carbon dioxide released from the burning of fossil fuels is not absorbed by vegetation and the oceans and remains in the atmosphere.
   By adding sufficient oxygen to compensate for the metabolic usage, removing the carbon dioxide, and rebreathing the gas, most of the volume is conserved.
  
  Section::::History.
  
  Section::::History.:Early history.
   In individuals with chronic obstructive pulmonary disease who receive supplemental oxygen, carbon dioxide accumulation may occur through two main mechanisms:
  
  BULLET::::- Ventilation/perfusion matching: under-ventilated lung usually has a low oxygen content which leads to localised vasoconstriction limiting blood flow to that lung tissue. Supplemental oxygen abolishes this constriction, leading to poor ventilation/perfusion matching. This redistribution of blood to areas of the lung with poor ventilation reduces the amount of carbon dioxide eliminated from the system.
   Carbon dioxide is not expelled completely when the diver exhales into apparatus with mechanical dead space, such as a long snorkel, full face diving mask, or diving helmet, and then inhales from the dead space.
   Carbon dioxide removal is different from reducing emissions, as the former produces an outlet of carbon dioxide from Earth's atmosphere, whereas the latter decreases the inlet of carbon dioxide to the atmosphere. Both have the same net effect, but for achieving carbon dioxide concentration levels below present levels, carbon dioxide removal is critical. Also for meeting higher concentration levels, carbon dioxide removal is increasingly considered to be crucial as it provides the only possibility to fill the gap between needed reductions to meet mitigation targets and .
   Oxygen has a very low solubility in water, and is therefore carried in the blood loosely combined with hemoglobin. The oxygen is held on the hemoglobin by four ferrous iron-containing heme groups per hemoglobin molecule. When all the heme groups carry one O molecule each the blood is said to be “saturated” with oxygen, and no further increase in the partial pressure of oxygen will meaningfully increase the oxygen concentration of the blood. Most of the carbon dioxide in the blood is carried as bicarbonate ions (HCO) in the plasma. However the conversion of dissolved CO into HCO (through the addition of water) is too slow for the rate at which the blood circulates through the tissues on the one hand, and through alveolar capillaries on the other. The reaction is therefore catalyzed by carbonic anhydrase, an enzyme inside the red blood cells. The reaction can go in both directions depending on the prevailing partial pressure of CO. A small amount of carbon dioxide is carried on the protein portion of the hemoglobin molecules as carbamino groups. The total concentration of carbon dioxide (in the form of bicarbonate ions, dissolved CO, and carbamino groups) in arterial blood (i.e. after it has equilibrated with the alveolar air) is about 26 mM (or 58 ml/100 ml), compared to the concentration of oxygen in saturated arterial blood of about 9 mM (or 20 ml/100 ml blood).
   Carbon dioxide is an end product of cellular respiration in organisms that obtain energy by breaking down sugars, fats and amino acids with oxygen as part of their metabolism. This includes all plants, algae and animals and aerobic fungi and bacteria. In vertebrates, the carbon dioxide travels in the blood from the body's tissues to the skin (e.g., amphibians) or the gills (e.g., fish), from where it dissolves in the water, or to the lungs from where it is exhaled. During active photosynthesis, plants can absorb more carbon dioxide from the atmosphere than they release in respiration.
   As a person breathes, the body consumes oxygen and produces carbon dioxide. Base metabolism requires about 0.25 L/min of oxygen from a breathing rate of about 6 L/min, and a fit person working hard may ventilate at a rate of 95 L/min but will only metabolise about 4 L/min of oxygen The oxygen metabolised is generally about 4% to 5% of the inspired volume at normal atmospheric pressure, or about 20% of the available oxygen in the air at sea level. Exhaled air at sea level contains roughly 13.5% to 16% oxygen.
   Section::::Methods.:Enhanced weathering.
   Levels of CO rise in the blood when the metabolic use of O, and the production of CO is increased during, for example, exercise. The CO in the blood is transported largely as bicarbonate (HCO) ions, by conversion first to carbonic acid (HCO), by the enzyme carbonic anhydrase, and then by disassociation of this acid to H and HCO. Build-up of CO therefore causes an equivalent build-up of the disassociated hydrogen ions, which, by definition, decreases the pH of the blood. The pH sensors on the brain stem immediately sense to this fall in pH, causing the respiratory center to increase the rate and depth of breathing. The consequence is that the partial pressure of CO (PCO2) does not change from rest going into exercise. During very short-term bouts of intense exercise the release of lactic acid into the blood by the exercising muscles causes a fall in the blood plasma pH, independently of the rise in the PCO2, and this will stimulate pulmonary ventilation sufficiently to keep the blood pH constant at the expense of a lowered PCO2.
   Plant respiration is limited by the process of diffusion. Plants take in carbon dioxide through holes, known as stomata, that can open and close on the undersides of their leaves and sometimes other parts of their anatomy. Most plants require some oxygen for catabolic processes (break-down reactions that release energy). But the quantity of O used per hour is small as they are not involved in activities that require high rates of aerobic metabolism. Their requirement for air, however, is very high as they need CO for photosynthesis, which constitutes only 0.04% of the environmental air. Thus, to make 1 g of glucose requires the removal of all the CO from "at least" 18.7 liters of air at sea level. But inefficiencies in the photosynthetic process cause considerably greater volumes of air to be used.
   Activated carbon can be used as a carbon dioxide scrubber. Air with high carbon dioxide content, such as air from fruit storage locations, can be blown through beds of activated carbon and the carbon dioxide will absorb onto the activated carbon. Once the bed is saturated it must then be "regenerated" by blowing low carbon dioxide air, such as ambient air, through the bed. This will release the carbon dioxide from the bed, and it can then be used to scrub again, leaving the net amount of carbon dioxide in the air the same as when the process was started. 
   Methane and power produced in anaerobic digestion facilities can be used to replace energy derived from fossil fuels, and hence reduce emissions of greenhouse gases, because the carbon in biodegradable material is part of a carbon cycle. The carbon released into the atmosphere from the combustion of biogas has been removed by plants for them to grow in the recent past, usually within the last decade, but more typically within the last growing season. If the plants are regrown, taking the carbon out of the atmosphere once more, the system will be carbon neutral. In contrast, carbon in fossil fuels has been sequestered in the earth for many millions of years, the combustion of which increases the overall levels of carbon dioxide in the atmosphere.
   Biochemical composition of reserve and structure is considered to be that of generalised compounds, and is constant (the assumption of strong homeostasis) but not necessarily identical. Biochemical transformation from food to reserve (assimilation), and from reserve to structure (growth) include overhead costs. These overheads, together with processes of somatic and maturity maintenance and reproduction overheads (inefficiencies in transformation from reserve to reproductive material), all contribute to the consumption of oxygen and production of carbon dioxide, i.e. metabolism.
  
  Section::::DEB models.
   Section::::Biological role.:Human physiology.
  
  Section::::Biological role.:Human physiology.:Content.
  
  The body produces approximately of carbon dioxide per day per person, containing of carbon. In humans, this carbon dioxide is carried through the venous system and is breathed out through the lungs, resulting in lower concentrations in the arteries. The carbon dioxide content of the blood is often given as the partial pressure, which is the pressure which carbon dioxide would have had if it alone occupied the volume. In humans, the blood carbon dioxide contents is shown in the adjacent table:
  
  Section::::Biological role.:Human physiology.:Transport in the blood.
   In a normal resting state the work of breathing constitutes about 5% of the total body oxygen consumption. It can increase considerably due to illness or constraints on gas flow imposed by breathing apparatus, ambient pressure, or breathing gas composition.
  
  Section::::Mechanism of breathing.
  
  The normal relaxed state of the lung and chest is partially empty. Further exhalation requires muscular work.
   An additional source of atmospheric free oxygen comes from photolysis, whereby high-energy ultraviolet radiation breaks down atmospheric water and nitrous oxide into component atoms. The free H and escape into space, leaving O in the atmosphere: 
  
  Section::::Sources and sinks.:Biological consumption.
  
  The main way free oxygen is lost from the atmosphere is via respiration and decay, mechanisms in which animal life and bacteria consume oxygen and release carbon dioxide.
  
  Section::::Sources and sinks.:Abiotic consumption.
  
  The lithosphere also consumes atmospheric free oxygen by chemical weathering and surface reactions. An example of surface weathering chemistry is formation of iron oxides (rust): 
   As the source of available carbon in the carbon cycle, atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena. Plants, algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water, with oxygen produced as a waste product.
   Different GHGs last different amounts of time in the atmosphere. For example, fluorinated gases can last from a few weeks to a few thousand years in the atmosphere, whereas nitrous oxide can last for over a century. However, methane is somewhere in the middle, lasting a little over a decade. Carbon dioxide's lifespan cannot be calculated exactly because it does not disappear, but is either used by plants or absorbed by the ocean. There is a possibility that some greenhouse gases have been in the atmosphere since the beginning of the twentieth century, when the first signs of an increase of these gases arose.
   Therefore, the respiratory minute volume may be expressed as a function of the extraction ratio and oxygen uptake:
  
  The volume of gas in the breathing circuit can be described as approximately constant, and the fresh gas addition must balance the sum of the dumped volume, the metabolically removed oxygen, and the volume change due to depth change. (metabolic carbon dioxide added to the mixture is removed by the scrubber and therefore does not affect the equation)
   Most sources of emissions are natural, and are balanced to various degrees by natural sinks. For example, the natural decay of organic material in forests and grasslands and the action of forest fires results in the release of about 439 gigatonnes of carbon dioxide every year, while new growth entirely counteracts this effect, absorbing 450 gigatonnes per year. Although the initial carbon dioxide in the atmosphere of the young Earth was produced by volcanic activity, modern volcanic activity releases only 130 to 230 megatonnes of carbon dioxide each year. These natural sources are nearly balanced by natural sinks, physical and biological processes which remove carbon dioxide from the atmosphere. For example, some is directly removed from the atmosphere by land plants for photosynthesis and it is soluble in water forming carbonic acid. There is a large natural flux of into and out of the biosphere and oceans. In the pre-industrial era these fluxes were largely in balance. Currently about 57% of human-emitted is removed by the biosphere and oceans. From pre-industrial era to 2010, the terrestrial biosphere represented a net source of atmospheric prior to 1940, switching subsequently to a net sink. The ratio of the increase in atmospheric to emitted is known as the "airborne fraction" (Keeling et al., 1995); this varies for short-term averages and is typically about 45% over longer (5 year) periods. Estimated carbon in global terrestrial vegetation increased from approximately 740 billion tons in 1910 to 780 billion tons in 1990.
   In 2008, the Discovery Channel covered the work of David Keith, of University of Calgary, who built a tower, 4 feet wide and 20 feet tall (1.2×6.1 meters), with a fan at the bottom that sucks air in, which comes out again at the top. In the process, about half the CO is removed from the air.
   Section::::History.
  
raw_presuppositions: The body wastes oxygen when breathing it out with carbon dioxide. We still need the oxygen that is present in carbon dioxide when we breathe it out.
raw_corrections: The body does not need oxygen, but the energy in oxygen. We no longer need the oxygen that is present in carbon dioxide when we breathe it out.