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Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane , or a biological membrane that forms the boundary between an organism and its extracellular environment.
Cutaneous respiration, or cutaneous gas exchange (sometimes called skin breathing), [1] is a form of respiration in which gas exchange occurs across the skin or outer integument of an organism rather than gills or lungs. Cutaneous respiration may be the sole method of gas exchange, or may accompany other forms, such as ventilation.
Breathing, or external respiration, brings air into the lungs where gas exchange takes place in the alveoli through diffusion. The body's circulatory system transports these gases to and from the cells, where cellular respiration takes place. [2] [3]
Exchange of gases in the lung occurs by ventilation and perfusion. [1] Ventilation refers to the in-and-out movement of air of the lungs and perfusion is the circulation of blood in the pulmonary capillaries. [1] In mammals, physiological respiration involves respiratory cycles of inhaled and exhaled breaths.
In fish, for example, they have: A large surface area to allow as much oxygen to enter the gills as possible because more of the gas comes into contact with the membrane; Good blood supply to maintain the concentration gradient needed; Thin membrane to allow for a short diffusion pathway; Each gill arch has two rows (hemibranchs) of gill filaments
A biological example of diffusion is the gas exchange that occurs during respiration within the human body. [7] Upon inhalation, oxygen is brought into the lungs and quickly diffuses across the membrane of alveoli and enters the circulatory system by diffusing across the membrane of the pulmonary capillaries. [8]
Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles.
Aerenchyma in stem cross section of a typical wetland plant. Aerenchyma or aeriferous parenchyma [1] or lacunae, is a modification of the parenchyma to form a spongy tissue that creates spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the root. [2]