gasexchanging

Gas exchange, sometimes informally referred to as gasexchanging in older texts, is the biological process by which oxygen is taken up by an organism and carbon dioxide is released to the environment, enabling cellular respiration and metabolism. It occurs across specialized surfaces or tissues that allow gases to diffuse down their partial pressure gradients. In animals, gas exchange typically takes place across respiratory surfaces such as lungs, gills, or, in some simpler organisms, the body surface. In plants, gas exchange occurs primarily through stomata on the leaf surface, where openings regulate the uptake of carbon dioxide for photosynthesis and the release of oxygen.

In vertebrates, lungs provide a large, thin interface between air and blood. In mammals, oxygen diffuses from air in the alveoli into the blood, while carbon dioxide diffuses from blood into the alveolar air for exhalation. The alveolar–capillary interface and the abundance of alveoli maximize diffusion. In fish, gills expose blood to flowing water; gill lamellae and a countercurrent arrangement optimize oxygen uptake. Insects rely on an internal tracheal system that delivers air directly to tissues, reducing dependence on circulatory transport for diffusion over long distances.

In plants, gas exchange is closely linked to photosynthesis and respiration. CO2 diffuses into leaves through stomata, while O2 and water vapor exit. Guard cells regulate stomatal aperture in response to light, humidity, CO2 concentration, and water status. Leaf anatomy, stomatal density, and cuticle properties influence diffusion rates.

Gas exchange efficiency depends on surface area, diffusion distance, and the gradient of partial pressures, as well as temperature and membrane permeability. Disruptions can affect health and performance in animals and can limit photosynthetic productivity in plants.