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While animals and physical factors (i.e. wind, water, etc.) have played a role in dispersal for centuries, motor vehicles have recently been considered as major dispersal vectors. Tunnels that connect rural and urban environments have been shown to expedite a large amount of and diverse set of seeds from urban to rural environments.
It is usually observed in large plant and animal cells, greater than approximately 0.1 mm [vague]. 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]
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.
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.
The self-diffusion coefficient of neat water is: 2.299·10 −9 m 2 ·s −1 at 25 °C and 1.261·10 −9 m 2 ·s −1 at 4 °C. [2] Chemical diffusion occurs in a presence of concentration (or chemical potential) gradient and it results in net transport of mass. This is the process described by the diffusion equation.
English: Schematic diffusion profile of an element across growth zones of an igneous mineral; graph depicts position (x) and concentration (C). The blue zones are representative of igneous growth zones of a mineral, with an initially sharp concentration gradient between zones (represented by dashed blue line on graph).
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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]