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Cross-sectional view of the structures that can be formed by phospholipids in an aqueous solution. A biological membrane, biomembrane or cell membrane is a selectively permeable membrane that separates the interior of a cell from the external environment or creates intracellular compartments by serving as a boundary between one part of the cell and another.
As mentioned above, passive diffusion is a spontaneous phenomenon that increases the entropy of a system and decreases the free energy. [5] The transport process is influenced by the characteristics of the transport substance and the nature of the bilayer. The diffusion velocity of a pure phospholipid membrane will depend on: concentration ...
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]
"Bulk flow" is the movement/flow of an entire body due to a pressure gradient (for example, water coming out of a tap). "Diffusion" is the gradual movement/dispersion of concentration within a body with no net movement of matter. An example of a process where both bulk motion and diffusion occur is human breathing. [2]
Diffusion is also faster in smaller, lighter molecules of which helium is the extreme example. Diffusivity of helium is 2.65 times faster than nitrogen. [14] The partial pressure gradient, also known as the concentration gradient, can be used as a model for the driving mechanism of diffusion. The partial pressure gradient is the rate of ...
The microscopic structure of a gill presents a large surface area to the external environment. Branchia ( pl. : branchiae) is the zoologists' name for gills (from Ancient Greek βράγχια ). With the exception of some aquatic insects , the filaments and lamellae (folds) contain blood or coelomic fluid , from which gases are exchanged ...
Facilitated diffusion in cell membrane, showing ion channels and carrier proteins. Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins. [1]
An example of an antiporter mediated transport protein is the sodium-calcium antiporter, a transport protein involved in keeping the cytoplasmic concentration of calcium ions in the cells, low. This transport protein is an antiporter system because it transports three sodium ions across the plasma membrane in exchange for a calcium ion, which ...