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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]
In smaller cells, the diffusion of molecules is more rapid, but diffusion slows as the size of the cell increases, so larger cells may need cytoplasmic streaming for efficient function. [1] The green alga genus Chara possesses some very large cells, up to 10 cm in length, [2] and cytoplasmic streaming has been studied in these large cells. [3]
Cellular atrophy is a decrease in cell size. If enough cells in an organ undergo atrophy the entire organ will decrease in size. Thymus atrophy during early human development (childhood) is an example of physiologic atrophy. Skeletal muscle atrophy is a common pathologic adaptation to skeletal muscle disuse (commonly called "disuse atrophy").
In biology, the solutions on either side of a cell membrane are isotonic if the concentration of solutes outside the cell is equal to the concentration of solutes inside the cell. In this case the cell neither swells nor shrinks because there is no concentration gradient to induce the diffusion of large amounts of water across the cell membrane.
Passive diffusion across a cell membrane.. Passive transport is a type of membrane transport that does not require energy to move substances across cell membranes. [1] [2] Instead of using cellular energy, like active transport, [3] passive transport relies on the second law of thermodynamics to drive the movement of substances across cell membranes.
Diffusion through the capillary walls depends on the permeability of the endothelial cells forming the capillary walls, which may be continuous, discontinuous, and fenestrated. [4] The Starling equation describes the roles of hydrostatic and osmotic pressures (the so-called Starling forces ) in the movement of fluid across capillary endothelium .
D is the diffusion constant of the solute unit m 2 ⋅s −1, t is time unit s, c 2, c 1 concentration should use unit mol m −3, so flux unit becomes mol s −1. The flux is decay over the square root of time because a concentration gradient builds up near the membrane over time under ideal conditions.
Light micrograph of a moss's leaf cells at 400X magnification. The following outline is provided as an overview of and topical guide to cell biology: . Cell biology – A branch of biology that includes study of cells regarding their physiological properties, structure, and function; the organelles they contain; interactions with their environment; and their life cycle, division, and death.