The four main kinds of passive transport are simple diffusion, facilitated diffusion, filtration, and/or osmosis.
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There are different ways through which cells can transport substances across the cell membrane. The two main pathways are passive transport and active transport. Passive transport is more direct and does not require the use of the cell's energy. It relies on an area that maintains a high-to-low concentration gradient.
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Section 15.6, Cotransport by Symporters and Antiporters. This involves pore-forming proteins that form channels across the cell membrane. The difference between passive transport and active transport is that the active transport requires energy, and moves substances against their respective concentration gradient, whereas passive transport requires no cellular energy and moves substances in the direction of their respective concentration gradient.Lodish H, Berk A, Zipursky SL, et al.
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That is, as solutes are off- loaded into sink cells (by active or passive transport), the density of the phloem liquid decreases locally, creating a pressure gradient.
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Passive diffusion across a cell membrane. Passive transport is a movement of ions and other atomic or molecular substances across cell membranes without need of energy input. Unlike active transport, it does not require an input of cellular energy because it is instead driven by the tendency of the system to grow in entropy. The rate of passive transport depends on the permeability of the cell membrane, which, in turn, depends on the organization and characteristics of the membrane lipids and proteins.
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Natural dispersal of this snail is known to occur by passive transport in birds. Bithynia tentaculata is capable of detecting the presence of molluscivorous leeches through chemoreception and of closing its operculum to avoid predation.
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Passive osmosis and diffusion: Some substances (small molecules, ions) such as carbon dioxide (CO2) and oxygen (O2), can move across the plasma membrane by diffusion, which is a passive transport process. Because the membrane acts as a barrier for certain molecules and ions, they can occur in different concentrations on the two sides of the membrane. Diffusion occurs when small molecules and ions move freely from high concentration to low concentration in order to equilibrate the membrane. It is considered a passive transport process because it does not require energy and is propelled by the concentration gradient created by each side of the membrane.
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Carrier proteins are integral membrane proteins; that is, they exist within and span the membrane across which they transport substances. 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.
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The wax, which sticks to each egg, also facilitates passive transport by animals or man. Reproduction may occur by means of parthenogenesis in the absence of the male. Newly hatched nymphs are called crawlers and are very mobile. They may disperse over the host, especially toward tender growing parts, or be carried away by wind, man, or animals.
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Channels perform passive transport of materials also known as facilitated diffusion. Transporters can carry out either passive or active transfer of materials while pumps require energy to act.Lodish, H., Berk, A., Kaiser, C., Krieger, M., Scott, M., Bretscher, A., Ploegh, H., and Matsudaira, P. (2008) Molecular Cell Biology, 6th ed. (New York: W. H. Freeman) pp. 437 – 474.
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When only a few individuals attempt to disperse, they are frequently subjects of predation. While voluntary dispersion may not often occur, animal dispersion occasionally does, as dispersion over large distances is likely to be passive transport by bats or other vertebrates. Passive animal dispersion may occur often enough that selection has not favored active dispersion. Limited dispersion, however, can be consequential.
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The currently known aquaporins cluster loosely together as do the known glycerol facilitators. MIP family proteins are believed to form aqueous pores that selectively allow passive transport of their solute(s) across the membrane with minimal apparent recognition. Aquaporins selectively transport glycerol as well as water while glycerol facilitators selectively transport glycerol but not water. Some aquaporins can transport NH3 and CO2.
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Once the vesicles pinch off from the ER they are transported passively (by diffusion) or actively (by intracellular motors that run on cytoskeletal tracks). The mode of transport seems to be influenced by distance. Short distances may tend towards passive transport, whereas longer distances tend towards active transport. Once these vesicles reach their destination, they need to be first physically linked with their acceptor compartment (else they may float away).
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There is an upregulation of this SUR1/ TRPM4 nonselective cation channel followed by brain tumor, ischemic injury, and traumatic brain injury. This channel which is activated by ATP depletion is found on neurons, neuroglia and endothelium. This channel enables the passive transport of water and solute and represents the ATP independent stage of cerebral formation. Opening of these channels result in cellular depolarization and blebbing causing cytotoxic edema.
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Depiction of facilitated diffusion. Facilitated diffusion, also called carrier-mediated osmosis, is the movement of molecules across the cell membrane via special transport proteins that are embedded in the plasma membrane by actively taking up or excluding ions. Active transport of protons by H+ ATPases alters membrane potential allowing for facilitated passive transport of particular ions such as potassium down their charge gradient through high affinity transporters and channels.
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The main characteristic of underground environment is the lack of sunlight. Climatic values, like temperature and relative humidity, are generally almost stable – temperature corresponds to annual mean temperature in the place where the cavity opens, relative humidity rarely drops below 90%. Food sources are limited and localized. The lack of sunlight inhibits photosynthetic processes, so food comes only from epigean environment (through percolating water, gravity, or passive transport by animals).
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Maternal side of a placenta shortly after birth. The placenta intermediates the transfer of nutrients between mother and fetus. The perfusion of the intervillous spaces of the placenta with maternal blood allows the transfer of nutrients and oxygen from the mother to the fetus and the transfer of waste products and carbon dioxide back from the fetus to the maternal blood. Nutrient transfer to the fetus can occur via both active and passive transport.
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The chemical structure of the outer membrane lipopolysaccharides is often unique to specific bacterial strains (i.e. sub- species) and is responsible for many of the antigenic properties of these strains. As a phospholipid bilayer, the lipid portion of the outer membrane is largely impermeable to all charged molecules. However, channels called porins are present in the outer membrane that allow for passive transport of many ions, sugars and amino acids across the outer membrane.
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Journal of Cell Science 24, 2107 - 2112. Ion channels are a type of transmembrane channel responsible for the passive transport of positively charged ions (sodium, potassium, calcium, hydrogen and magnesium) and negatively charged ions (chloride) and, can be either gated or ligand-gated channels. One of the best studied ion channels is the potassium ion channel. The potassium ion channel can allow rapid movement of potassium ions while being selective against sodium.
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Palytoxin targets the sodium-potassium pump protein by locking it into a position where it allows passive transport of both sodium and potassium ions, thereby destroying the ion gradient that is essential for life. Because palytoxin can affect every type of cell in the body, the symptoms can be very different for the various routes of exposure. Palytoxin's planar chemical structure was solved in 1981 by two research groups independently from each other. Stereochemistry was solved in 1982.
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In these cases, the dispersal units are moved to new aquatic habitats by utilizing the wind instead of the water in their habitat. Flowing rivers can act as dispersal vectors for plant matter and invertebrates. Running water is the only form of long distance dispersal present in freshwater sources, so rivers act as the main aquatic terrestrial dispersal vector. Like in marine ecosystems, organisms take advantage of flowing water via passive transport of drifting along on a raft.
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Dually, one can view processes occurring in nature as information processing. Such processes include self-assembly, developmental processes, gene regulation networks, protein–protein interaction networks, biological transport (active transport, passive transport) networks, and gene assembly in unicellular organisms. Efforts to understand biological systems also include engineering of semi-synthetic organisms, and understanding the universe itself from the point of view of information processing. Indeed, the idea was even advanced that information is more fundamental than matter or energy.
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Ionophores facilitate the transport of ions across biological membranes most commonly via passive transport, which is affected by lipophilicity of the ionophore molecule. The increase in lipophilicity of the ionophore-metal complex enhances its permeability through lipophilic membranes. The hydrophobicity and hydrophilicity of the complex also determines whether it will slow down or ease the transport of metal ions into cell compartments. The reduction potential of a metal complex influences its thermodynamic stability and affects its reactivity.
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Unlike passive transport, which uses the kinetic energy and natural entropy of molecules moving down a gradient, active transport uses cellular energy to move them against a gradient, polar repulsion, or other resistance. Active transport is usually associated with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. Examples of active transport include the uptake of glucose in the intestines in humans and the uptake of mineral ions into root hair cells of plants.
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Most of the reabsorption (65%) occurs in the proximal tubule. In the latter part it is favoured by an electrochemical driving force, but initially it needs the cotransporter SGLT and the Na-H antiporter. Sodium passes along an electrochemical gradient (passive transport) from the lumen into the tubular cell, together with water and chloride which also diffuse passively. Water is reabsorbed to the same degree, resulting in the concentration in the end of the proximal tubule being the same as in the beginning.
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However, in many cases (e.g. passive drug transport) the driving force of passive transport can not be simplified to the concentration gradient. If there are different solutions at the two sides of the membrane with different equilibrium solubility of the drug, the difference in the degree of saturation is the driving force of passive membrane transport. It is also true for supersaturated solutions which are more and more important owing to the spreading of the application of amorphous solid dispersions for drug bioavailability enhancement.
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Given the low concentration of fertile eggs on infected dogs' coats (less than 0.00186% per gram), it is plausible that such eggs were transferred to the dog's coat by contact with fecal deposits in the environment, making dog coats the passive transport host vehicle. However, although the risk of being infected by petting a dog is extremely limited, a single infected puppy can produce more than 100,000 roundworm eggs per gram of feces."Round Worms from an infected puppy" "TheDoctorsTv". Published 3-19-2012.
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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. Being passive, facilitated transport does not directly require chemical energy from ATP hydrolysis in the transport step itself; rather, molecules and ions move down their concentration gradient reflecting its diffusive nature. Insoluble molecules diffusing through an integral protein. Facilitated diffusion is different from simple diffusion in several ways.
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In the liver cell, it is phosphorylated by glucokinase at position 6 to glucose-6-phosphate, which can not leave the cell. With the help of glucose-6-phosphatase, glucose-6-phosphate is converted back into glucose exclusively in the liver, if necessary, so that it is available for maintaining a sufficient blood glucose concentration. In other cells, uptake happens by passive transport through one of the 14 GLUT proteins. In the other cell types, phosphorylation occurs through a hexokinase, whereupon glucose can no longer diffuse out of the cell.
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Once chromium(III) picolinate is ingested and enters the stomach, acidic hydrolysis of the complex occurs when in contact with the stomach mucosa. The hydrolyzed Cr3+ is present in the hexaaqua form and polymerizes to form an insoluble Cr(III)-hydroxide-oxide (the process of olation) once it reaches the alkaline pH of the small intestine. Approximately 2% of Cr3+ is absorbed through the gut as chromium(III) picolinate via unsaturated passive transport. Although absorption is low, CrPic3 absorbs more efficiently than other organic and inorganic sources (i.e.
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The interior surface of the jejunum—which is exposed to ingested food—is covered in finger–like projections of mucosa, called villi, which increase the surface area of tissue available to absorb nutrients from ingested foodstuffs. The epithelial cells which line these villi have microvilli. The transport of nutrients across epithelial cells through the jejunum and ileum includes the passive transport of sugar fructose and the active transport of amino acids, small peptides, vitamins, and most glucose. The villi in the jejunum are much longer than in the duodenum or ileum.
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Mechanisms of transport: (L) channel, (M) ionophore/carrier, and (R) detergent Passive transport of ions across a membrane can take place by three main mechanisms: by ferrying, through defects in a disrupted membrane, or through a defined trajectory; these corresponds to ionophore, detergent, and ion channel transporters. While synthetic ion channel research attempts to prepare compounds that show conductance via a defined path, the elucidation of mechanism is difficult and seldom unambiguous. The two main methods of characterization both have their drawbacks, and as a consequence, often function is defined but mechanism presumed.
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Simple diffusion and osmosis are in some ways similar. Simple diffusion is the passive movement of solute from a high concentration to a lower concentration until the concentration of the solute is uniform throughout and reaches equilibrium. Osmosis is much like simple diffusion but it specifically describes the movement of water (not the solute) across a selectively permeable membrane until there is an equal concentration of water and solute on both sides of the membrane. Simple diffusion and osmosis are both forms of passive transport and require none of the cell's ATP energy.
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The movement by animals of items involved in plant reproduction is usually a mutualistic association. Pollinators may increase plant reproductive success by reducing pollen waste, increasing dispersal of pollen, and increasing the probability of sexual reproduction at low population density. In return, the pollinator receives nourishment in the form of nectar or pollen. Animals may also disperse the seed or fruit of plants, either by eating it (in which case they receive the benefit of nourishment) or by passive transport, such as seeds sticking to fur or feathers.
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Their transport must therefore be "facilitated" by proteins that span the membrane and provide an alternative route or bypass mechanism. Some examples of proteins that mediate this process are glucose transporters, organic cation transport proteins, urea transporter, monocarboxylate transporter 8 and monocarboxylate transporter 10. Various attempts have been made by engineers to mimic the process of facilitated transport in synthetic (i.e., non-biological) membranes for use in industrial- scale gas and liquid separations, but these have met with limited success to date, most often for reasons related to poor carrier stability and/or dissociation of the carrier from the passive transport.
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Certain vesicle- trafficking steps require the transportation of a vesicle over a moderately small distance. For example, vesicles that transport proteins from the Golgi apparatus to the cell surface area, will be likely to use motor proteins and a cytoskeletal track to get closer to their target. Before tethering would have been appropriate, many of the proteins used for the active transport would have been instead set for passive transport, because the Golgi apparatus does not require ATP to transport proteins. Both the actin- and the microtubule- base are implicated in these processes, along with several motor proteins.
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Primarily produced by Gram-negative bacteria, acylated homoserine lactones (AHLs) are a class of small neutral lipid molecules composed of a homoserine lactone ring with an acyl chain. AHLs produced by different species of Gram-negative bacteria vary in the length and composition of the acyl side chain, which often contains 4 to 18 carbon atoms. AHLs are synthesized by AHL synthases. They diffuse in and out of cells by both passive transport and active transport mechanisms. Receptors for AHLs include a number of transcriptional regulators called “R proteins,” which function as DNA binding transcription factors or sensor kinases.
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An electrochemical gradient or concentration gradient is a difference in concentration of a chemical molecule or ion in two separate areas. At equilibrium the concentrations of the ion in both areas will be equal, so if there is a difference in concentration the ions will seek to flow "down" the concentration gradient or from a high concentration to low concentration. Ion channels allows the specific ions that will fit into the channel to flow down their concentration gradient, equalizing the concentrations on either side of the cell membrane. Ion channels accomplish this via facilitated diffusion which is a type of passive transport.
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Schematic of semipermeable membrane during hemodialysis, where blood is red, dialysing fluid is blue, and the membrane is yellow. Semipermeable membrane is a type of biological or synthetic, polymeric membrane that will allow certain molecules or ions to pass through it by Osmosis—or occasionally by more specialized processes of facilitated diffusion, passive transport or active transport. 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. Depending on the membrane and the solute, permeability may depend on solute size, solubility, properties, or chemistry.
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These energetically free (resistors or conductors, passive transport) or expensive (current sources, active transport) translocators set and fine tune voltage gradients – resting potentials – that are ubiquitous and essential to life's physiology, ranging from bioenergetics, motion, sensing, nutrient transport, toxins clearance, and signaling in homeostatic and disease/injury conditions. Upon stimuli or barrier breaking (short-circuit) of the membrane, ions powered by the voltage gradient (electromotive force) diffuse or leak, respectively, through the cytoplasm and interstitial fluids (conductors), generating measurable electric currents – net ion fluxes – and fields. Some ions (such as calcium) and molecules (such as hydrogen peroxide) modulate targeted translocators to produce a current or to enhance, mitigate or even reverse an initial current, being switchers. Endogenous bioelectric signals are produced in cells by the cumulative action of ion channels, pumps, and transporters.
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Likewise, the loop of Henle requires a number of different cell types because each cell type has distinct transport properties and characteristics. These include the descending limb cells, thin ascending limb cells, thick ascending limb cells, cortical collecting duct cells and medullary collecting duct cells. One step towards validating the microfluidic device's simulation of the full filtration and reabsorption behavior of a physiological nephron would include demonstrating that the transport properties between blood and filtrate are identical with regards to where they occur and what is being let in by the membrane. For example, the large majority of passive transport of water occurs in the proximal tubule and the descending thin limb, or the active transport of NaCl largely occurs in the proximal tubule and the thick ascending limb.
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Micro-nutrient transfer is thought, for the most part, to occur by passive transport across cellular membranes, both during absorption, from soil by fungi, and transfer from fungi to host plants. This is not always the case though and although research on the topic is limited, there is evidence of active transport and allocation of micro-nutrients in certain conditions. The upregulation of cation transporters is observed in orchid D. officinale symbioses, suggesting fungi may assisted in the transfer of nutrients from fungi to plant. Cations, especially iron, are often bound tightly to organic and clay substrates keeping them out of reach of plants, fungi and bacteria, but compounds such as siderophores are often secreted into the soil by fungi and bacteria to aid in the acquisition of these cations.
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Chloride ion channels vary from many other ion channels due to being controlled by the anionic chloride ions. Chloride ion channels are pore- forming membrane proteins that allow the passive transport of chloride ions across biological membranes. Chloride ion channels involve both voltage-gated and ligand-gated mechanisms to transport the ions across cellular membranes. Chloride ion channels have been found to play crucial roles in the development of human diseases, for example, mutations in the genes encoding chloride ion channels lead to a variety of deleterious diseases in muscle, kidney, bone, and brain, including cystic fibrosis, osteoporosis, and epilepsy, and similarly their activation is supposed to be responsible for the progression of glioma in the brain and the growth of malaria-parasite in the red blood cells.
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