So long as men can breathe, or eyes can see,
So long lives this, and this gives life to thee.
— William Shakespeare, Sonnet 18

Respiration: a chemical process in which oxygen is used to make energy from carbohydrates. (NCI3) A process by which living cells obtain energy from organic molecules. (Brooker, G-6)

The biochemical “pathway” which takes place in cells and results in the release of "energy" from "organic" molecules. This energy is usually used to form “ATP,” although some is always lost as heat. The process can take place either in the presence of "oxygen" or in its absence. The only feature common to all respiratory pathways is the release of energy. (Indge, 233) Adjective - 'respiratory.' Also referred to as ‘cell respiration,’  ’cellular respiration,’  and ‘oxidative respiration.’

C6H12O6 + 6O2 --> 6H2O + 6CO2 + Energy


Aerobic Respiration: a type of respiration where O2 is consumed and CO2 is released. (Brooker, G-1) The long-term mode of energy conversion defined by the sufficient availability of oxygen to burn fuel—first "fat," and then fat and stored “glucose”—to feed active "muscle" cells. It occurs at low to moderately intense levels of physical activity and can be sustained over long periods of time. (Ratey, 275)

Anaerobic Respiration: the breakdown of organic molecules in the absence of oxygen. (Brooker, G-2) Products of anaerobic respiration, such as “lactic acid,” are eventually secreted from cells. During wine making, a "yeast" cell “metabolizes” sugar under anaerobic conditions. (Brooker, 145)

Glycolysis: the part of respiration in which a molecule of glucose is broken into two 3-carbon "pyruvate" groups. It takes place in the “cytoplasm” of the cell and is common to both aerobic respiration and anaerobic respiration. (Indge, 127) A "metabolic pathway" that breaks down glucose into pyruvate. (Brooker, G-16) The goal of the whole glycolysis process is to generate "ADP." (Norman, 6/23/09) Glycolysis is the most widespread metabolic process. It occurs in all "kingdoms." It requires no oxygen. It generates two ATP (cellular energy) and two "NADH" (electron carrier) molecules. All ten steps of glycolysis occur in the cytoplasm. The molecules that catalyze each step are called “enzymes.” (Norman, 6/23/09) In glycolysis, "phosphate groups" are first added to the glucose molecule. In other words, the glucose molecule is “phosphorylated.” This phosphate is supplied by ATP. The phosphorylated sugar is then broken down to give two pyruvate groups. The breakdown process produces a total of four ATP molecules so, altogether, there is a net gain of two ATP molecules. The complete reaction is an “oxidation” reaction and releases “hydrogen." This is removed and used to reduce a "coenzyme" known as "NAD." (Indge, 127) Editor's note - glycolysis phases listed below in order of occurrence.

Investment Phase of Glycolysis: the first phase involves an energy investment. Two ATP molecules (the investment) are 'hydrolyzed.' (Brooker, 135-136) Editor’s note - includes steps 1, 2, and 3 of the 10-step process.

Cleavage Phase of Glycolysis: breaks a 6-carbon molecule into two molecules. (Brooker, 135-136) Editor’s note - includes steps 4 and 5 of the 10-step process.

Payoff Phase of Glycolysis: liberates energy. The two molecules (are then) broken down to 2 pyruvate molecules. This produces 2 molecules of "NADH" and 4 molecules of ATP. (Brooker, 135-136) Editor’s note - includes steps 6, 7, 8, 9, and 10 of the 10-step process.

Pyruvate: a product of glycolysis. A 3-carbon molecule. A substrate for fermentation. Pyruvate is reduced directly by NADH to form lactic acid. Useful products: cheese and yogurt. Waste product: lactate. In "alcohol" "fermentation" pyruvate is converted to ethanol in two steps. (Norman, 6/23/09) An intermediate compound in the metabolism of “carbohydrates,” proteins, and fats. (MeSH)

Respiratory Structures: the organs that are involved in breathing. These include the "nose," "throat," "larynx," "trachea," “bronchi,” and "lungs." (NCIt)

Airway: any of the passages of the respiratory system. (OxfordMed) The part of the respiratory system between the nose or mouth and the lungs. (NCIt)

Bronchi: tubes connecting the “trachea” and the lungs. (Lawrence) The large air passages that lead from the “trachea” to the lungs. (NCIt) Has cartilage and mucus glands in its wall. (Oxford)

Larynx: the area of the throat containing the vocal cords and used for breathing, swallowing, and talking. (NCIt) Organ responsible for the production of vocal sounds, also serving as an air passage conveying air from the pharynx to the lungs. (OxfordMed) Also referred to as ‘voice box.’

Lungs: a pair of organs in the chest that supply the body with oxygen, and remove “carbon dioxide” from the body. (NCIt) Fibrous elastic sacs that are expanded and compressed by movements of the ‘rib cage’ and ‘diaphragm’ during breathing. (OxfordMed) Specialized for the respiratory uptake of oxygen directly from air and release of carbon dioxide to the air. In mammals the lungs are paired masses of spongy tissue made up of finely divided airways lined with moist “epithelium.” These airways extend from the bronchi and end in small sacs providing a large surface area for gas exchange between air and bloodstream. (Lawrence)

Pharynx: a funnel-shaped ‘fibromuscular’ tube that conducts food to the “esophagus,” and air to the “larynx” and lungs. (MeSH) The hollow tube inside the neck that starts behind the nose and ends at the top of the windpipe and esophagus. The pharynx is about 5 inches long, depending on body size. (NCIt) Acts as a passageway for food from the mouth to the esophagus, and as an air passage from the nasal cavity and mouth to the larynx. (OxfordMed)

Throat: the hollow tube inside the neck that starts behind the nose and ends at the top of the trachea and esophagus. (NCIt)

Trachea: the airway that leads from the larynx to the bronchi. (NCIt) The upper part of the trachea lies just below the skin except where the thyroid gland is wrapped around it. (OxfordMed) Also referred to as ‘wind pipe.’