Where does respiration collide?

The set of metabolic reactions inside a cell that break down nutrients such as glucose and capture the released energy as ATP, the molecule cells spend to do work: in aerobic organisms this runs through glycolysis, the citric acid cycle, and a final electron transport chain that consumes oxygen. Mitchell's 1961 Coupling of Phosphorylation to Electron and Hydrogen Transfer by a Chemi-Osmotic type of Mechanism proposed that this last step stores energy as a proton gradient across a membrane and uses it to build ATP, the chemiosmotic account now central to how respiration is understood in biochemistry. The referent is an energy-conversion process running in every living cell, measured by oxygen used and ATP made, not the breathing of a whole animal or the carbon dioxide given off by a whole landscape.[1]

Unit

One chain of energy-releasing reactions in a cell, scaled by ATP yield per molecule of fuel

Recovery means

Not applicable

Measured by

Tracked by oxygen consumption, carbon dioxide production, and ATP or NADH turnover in cells or isolated mitochondria

The bodily act of moving air into and out of the lungs so that oxygen can pass into the blood and carbon dioxide can leave it, together with the rate at which this happens: in clinical use respiration usually means breathing, and the breathing rate is a basic vital sign. Cretikos and colleagues' 2008 Respiratory rate: the neglected vital sign reviewed how the number of breaths per minute signals deterioration in patients and argued it is too often overlooked at the bedside. The referent is the ventilatory exchange of gases by a whole body, counted in breaths per minute, not the chemical reactions of energy capture inside a single cell nor the carbon dioxide released by an entire ecosystem.[2]

Unit

One person's breathing, scaled as breaths per minute

Recovery means

Between breaths the lungs recoil and refill, and rate and depth adjust to demand

Measured by

Counted at the bedside as breaths per minute, or recorded by spirometry and capnography for volumes and gas exchange

The total release of carbon dioxide by all the living things in an ecosystem, the plants, animals, and microbes, as they break down organic matter for energy: ecosystem respiration is one of the two large flows in a landscape's carbon balance, set against the carbon that plants fix by photosynthesis. Lloyd and Taylor's 1994 On the Temperature Dependence of Soil Respiration gave a widely used equation for how the carbon dioxide given off by soil rises with temperature, a relation built into models of the whole-ecosystem flux. The referent is an aggregate carbon flow summed over a patch of land, measured in grams of carbon per area per time, not the breathing of one organism nor the ATP-making reactions inside one cell.[3]

Unit

The summed carbon dioxide loss of a whole ecosystem, per unit area per unit time

Recovery means

Not applicable

Measured by

Estimated from soil and chamber flux readings and from eddy-covariance towers that split net carbon exchange into respiration and photosynthesis