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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.
In contrast, paracellular transport is the transfer of substances across an epithelium by passing through an intercellular space between the cells. 1. It differs from transcellular transport, where the substances travel through the cell passing through both the apical membrane and basolateral membrane. 2. Renal physiology.
Semipermeable membrane is a type of synthetic or biologic, polymeric membrane that allows certain molecules or ions to pass through it by osmosis. The rate of passage depends on the pressure, concentration, and temperature of the molecules or solutes on either side, as well as the permeability of the membrane to each solute.
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 ...
Membrane transport protein. A membrane transport protein is a membrane protein involved in the movement of ions, small molecules, and macromolecules, such as another protein, across a biological membrane. Transport proteins are integral transmembrane proteins; that is they exist permanently within and span the membrane across which they ...
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]
The proteins may assist in the movement of substances by facilitated diffusion (i.e., passive transport) or active transport. These mechanisms of movement are known as carrier-mediated transport. [2] Each carrier protein is designed to recognize only one substance or one group of very similar substances.
Transcellular transport often involves energy expenditure whereas paracellular transport is unmediated and passive down a concentration gradient, [4] or by osmosis (for water) and solvent drag for solutes. [5] Paracellular transport also has the benefit that absorption rate is matched to load because it has no transporters that can be saturated.