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Topic: Concentration gradient

	Encyclopedia: Concentration gradient
		A concentration gradient is the difference in density of a substance over a distance.
		One of these species is allowed to flow from high to low concentration, which yields the entropic energy to drive the transport of the other solute from a low concentration region to a high one.
		Active transport typically moves molecules from low concentration to high, or against their concentration gradient, an process that would be entropically unfavorable were it not stoichiometrically coupled with the hydrolysis of ATP.
	www.nationmaster.com /encyclopedia/Concentration-gradient (240 words)

	Passive transport - Wikipedia, the free encyclopedia
		The difference of concentration between the two areas is often termed as the concentration gradient, and diffusion will continue until this gradient has been eliminated.
		Since diffusion moves material from area of higher concentration to the lower, it is described as moving solutes "down the concentration gradient" (compared with active transport, which often moves material from area of low concentration to area of higher concentration, and therefore referred to as moving the material "against the concentration gradient").
		Diffusion is biologically important because it enables the abolishment of concentration gradients in the body.
	en.wikipedia.org /wiki/Passive_transport (540 words)

	RTFTechnologies Ion Gradient Formation in Lithium Cells
		Concentration gradients form when the rate of ion generation is not matched in rate by ion transfer across the cell.
		During current generation, an ion gradient forms in a lithium cell since the rate of ion transport away from the anode and cathode of the cell is less than the rate at which the ions accumulate at the originating electrode.
		Concentration polarization reduces the output current by introducing a counter EMF in the electrolyte of a cell, therefore increasing the cell’s internal resistance to the flow of current.
	www.rtftechnologies.org /chemtech/licell.htm (3311 words)

	A new chemotaxis assay shows the extreme sensitivity of axons to molecular gradients - Nature Neuroscience (Site not responding. Last check: 2007-10-09)
		The sensitivity of DRG axons was measured by culturing explants in a three-dimensional collagen gel in the presence of an exponential NGF concentration gradient.
		Based on the less-quantitative experimental measurements of gradient sensitivity and the absolute concentration range that was previously available, we estimated the maximum distance an axon could be guided by a single gradient of exponential shape to be about 1 cm (ref. 31).
		For Figure 3c, procedures were the same, except that the concentration of NGF in the pump was varied to achieve the desired concentration at the explant position.
	www.nature.com /cgi-taf/DynaPage.taf?file=/neuro/journal/v7/n6/full/nn1259.html (4309 words)

	Small Molecule Transport (Site not responding. Last check: 2007-10-09)
		A substance diffuses down its own concentration gradient and is not affected by the gradients of other substances.
		Spontaneous process which is a function of a concentration gradient when a substance is more concentrated on one side of the membrane.
		For example, if two solutions of different concentrations are separated by a selectively permeable membrane that is permeable to water but not the solute, water will diffuse from the hypoosmotic solution to the hypertonic solution.
	home.earthlink.net /~dayvdanls/CampOLs/MemTransport.html (1663 words)

	VI. Mechanisms of Salt & Water Reabsorption
		concentration drops to a moderate extent in the initial 20% of the tubule and then remains constant for the remainder of the length of the tubule.
		The concentration gradient and the presence of a significant K conductance renders the cell electrically negative with respect to its surroundings.
		concentration in the tubular fluid and the disappearance of glucose and amino acids.
	www2.kumc.edu /ki/physiology/course/six/6_1.htm (1911 words)

	The Diffusion of Salt Solutions into Pure Water
		The method you will use to determine the concentration gradient of the solution as a function of time is based on the refraction of light.
		In this experiment the index of refraction gradient is measured by passing a laser light beam perpendicular to a glass stirring rod that acts as a cylindrical lens.
		If the line of light is passed through a solution of uniform concentration, the image on the other side of the diffusion cell, that we project on to a screen, is parallel and longer than the incoming image.
	www.chm.uri.edu /urichm/chm335/syllabus_2001/node13.html (718 words)

	EEOB 232 - Online Recitation (Site not responding. Last check: 2007-10-09)
		A concentration gradient is a difference in concentration of a particular substance between two adjacent areas.
		Since substances move from areas of high concentration to areas of low concentration, and there is more K+ inside the cell than outside the cell, K+ will want to exit the cell due to its concentration gradient.
		The movement of positively charged ions, based on their electrical gradient is similar to their movement in chemical gradients, in the sense that they move from a more positive area to a less positive area (don't let this statement confuse you).
	www.biosci.ohio-state.edu /~bmark/eeob232/ecgrad.html (479 words)

	[No title] (Site not responding. Last check: 2007-10-09)
		In some cases, the gradients exist across the diameter of a cell such that the leading most edge of a cell is exposed to a different concentration of agent than is the lagging edge of the cell.
		In other embodiments, the neither cell has migrated through the agent concentration gradient, but at least the second cell is present in a gradient such that the agent concentration at one end of the cell is different from the agent concentration at the opposite end of the cell.
		In some embodiments, the first concentration of agent is a zero concentration of agent, and the second concentration of agent is a non-zero concentration of agent, while in other embodiments the first concentration of agent is greater than the second concentration of agent.
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=04/53165.040805&ELEMENT_SET=DECL (10248 words)

	Lecture 8
		If the concentration of molecules is different in 2 regions (this produces a concentration gradient), diffusion will cause molecules to move from a region of high concentration to one of low concentration
		A flow or flux of a material is proportional to the gradient of force acting on the molecule.
		It is useful to think of a dilute solution as having a high water concentration and a concentrated solution as having a lower water concentration.
	members.aol.com /BearFlag45/Biology1A/LectureNotes/lec08.html (1719 words)

	Concentration gradient
		A 'concentration gradient layer' must use an effective dielectric function for which the first fit parameter is the volume fraction.
		Note the number three in the 7th column of the concentration gradient layer: This is the number of sublayers to be used for dividing the total thickness which is 10 nm in this case.
		A concentration gradient layer on the glass substrate is used with a mixture of SiO particles embedded in an SiO2 matrix.
	www.mtheiss.com /docs/scout2/concentration_gr.htm (713 words)

	Membrane Transport
		In this case, facilitated diffusion would be required because glucose needs transport channels to allow it to pass through the lipid bilayer of the plasma membrane.
		As the process continues and more and more glucose is removed from the fluid, the concentration gradient up which the glucose must be pumped - by active transport - increases.
		The problem is to pump glucose into the cell (where it is about 0.5 mM) and then across the plasma membrane at the basolateral surface of the cell into the interstitial fluid, where the glucose concentration is 5 mM (the same as in the blood).
	users.rcn.com /jkimball.ma.ultranet/BiologyPages/M/MembraneTransport.html (817 words)

	TRANSPORT MECHANISMS
		Osmosis is the movement of water from an area of low concentration of particles to an area of high concentration of particles (The particles are usually solute molecules dissolved in the water).
		Such high concentrations may be beneficial to the chemical reactions that are occurring on that side of the membrane.
		The concentration gradient and the charge gradient favors the diffusion of the Na+ back into the cell, but it can not pass through the phospholipid bilayer because of the charge on the Na+.
	www.mrs.umn.edu /~goochv/CellBio/lectures/transport/transport.html (2232 words)

	DIFFUSION THROUGH A CELL MEMBRANE (Site not responding. Last check: 2007-10-09)
		Since the net movement of diffusing molecules depends on the concentration gradient, the rate of diffusion is directly proportional to the concentration gradient (dC/dx) across the membrane.
		The concentration gradient, dC/dx, is the difference in molecule concentration inside and outside of the cell across a cell membrane of width dx.
		If the concentration of molecules outside the cell is very high relative to the internal cell concentration, the rate of diffusion will also be high.
	www.tiem.utk.edu /~gross/bioed/webmodules/diffusion.htm (930 words)

	Transport Across Membranes (Site not responding. Last check: 2007-10-09)
		That is, the movement of an ion from a high concentration to a low concentration is analogous to the movement of water (or some other liquid) from a high point to a lower point.
		The facilitated diffusion part is due to a dependence on movement only with the concentration gradient and a mechanism of passage through the membrane which employs membrane proteins.
		Consequently, the concentration of the original lipid bilayer-excluded substance inside the cell remains very low and the favorable gradient is maintained.
	www.mansfield.ohio-state.edu /~sabedon/biol1055.htm (2774 words)

	INTRODUCTION
		The concentration of a substance in a fluid is the number of molecules per unit volume.
		A gradient is a physical difference between 2 locations such that molecules tend to move from one region to the other.
		Osmosis depends on the concentration of water in both the cytoplasm and in the liquid that bathes the cell.
	www.sou.edu /BIOLOGY/Courses/PrinBi/Bi211/Roden/week5-review-02.htm (1410 words)

	LECTURE 16
		So if we start with a molecule that is at a high concentration on one side of the cell, and this molecule can pass through the membrane, at equili brium, the concentration of this molecule on both sides of the membrane will be the same.
		The side of the membrane with the higher concentration of sol ute is said to be hypertonic, while the other side is said to be hypotonic.
		The Na-K pump therefore generates not only a concentration gradient, but an electrical gradien t as well (it is therefore referd to as an electrogenic pump).
	www.ucc.uconn.edu /~giardina/LECTUR16.html (1909 words)

	Ionic Equilibria
		At equilibrium, the tendency of potassium ions to leave, driven by the concentration gradient, will be precisely balanced by the tendency of potassium ions to enter, driven by the electrical gradient.
		denote the potassium concentrations outside and inside, ln is the natural logarithm of the ratio inside the curly brackets, z is the valence of potassium (1), T is the temperature, and R and F are physical constants.
		If we increase the external concentration of sodium, that will increase the concentration gradient driving sodium ions in, and the voltage needed to counterbalance this will be a greater positive voltage.
	physioweb.med.uvm.edu /cardiacep/EP/equilibria.htm (1592 words)

	Electric circuits \|\| Concentration gradient
		Since the concentration gradient is linear, there will be the same strength of force on the electrons all along the wire.
		The concentration gradient stays the same but individual electrons will be moving ‘down’ the gradient all of the time.
		The gradient is maintained, so long as the chemical changes inside the battery feed in new electrons at the negative end and capture electrons as they enter the positive end.
	www.dur.ac.uk /p.m.johnson/electric_circuits/04_gradient.htm (238 words)

	Bioc 462a Lecture Notes
		Diffusion "down" the concentration gradient (from region of greater concentration to region of lower concentration, toward equilibrium of equal concentrations) is a manifestation of the 2nd law of thermodynamics -- molecules tend spontaneously to assume the distribution of greatest randomness, i.e., entropy increases until system is maximally randomized.
		Gradient of 2nd solute is another way to "store" potential energy that can be tapped to drive an unfavorable process.
		During passage of electrons along this chain, protons are pumped across the inner mitochondrial membrane, generating a proton gradient that is the driving force for the synthesis of ATP.
	www.biochem.arizona.edu /classes/bioc462/462a/NOTES/LIPIDS/transport.html (3655 words)

	Prokaryotic Cell Structure: The Cytoplasmic Membrane (Site not responding. Last check: 2007-10-09)
		5B), the water concentration is greater inside the cell while the solute concentration is higher outside (the interior of the cell is hypotonic to the surrounding hypertonic environment).
		5C), the water concentration is greater outside the cell and the solute concentration is higher inside (the interior of the cell is hypertonic to the hypotonic surroundings).
		Proton motive force is an energy gradient resulting from hydrogen ions (protons) moving across the membrane from greater to lesser hydrogen ion concentration.
	www.cat.cc.md.us /courses/bio141/lecguide/unit1/prostruct/cm.html (1981 words)

	Diffusion and Osmosis (Site not responding. Last check: 2007-10-09)
		A gradient is a general term for a difference in amount of something from one area to another.
		There is a concentration gradient when a solute is in higher concentration in one place than in another.
		But, if glucose is in a higher concentration outside of the cell than inside of the cell, the glucose concentration gradient is from outside to inside the cell, and glucose would be expected to move into the cell.
	distance.stcc.edu /BIOL102/Lectures/lesson7/diffos.htm (1113 words)

	Summary: Energy Calculations
		This would be the free energy available from a gradient of a nonionic solute, or from an ionic gradient if the movement of other ions maintained equal voltage on both sides of the membranes, as is true in chloroplasts.
		So in chloroplasts, the proton gradient is simply a concentration gradient, and there is no accompanying voltage gradient.
		There is no compensating movement of other charged ions, so pumping creates both a concentration gradient and a voltage gradient, the latter resulting from the excess of proton charges outside the inner mitochondrial membrane.
	www.usm.maine.edu /~rhodes/Goodies/Energetics.html (885 words)

	Membrane transport (Site not responding. Last check: 2007-10-09)
		Energy of ATP hydrolysis or energy derived from coupling transport of one solute against its concentration gradient with transport of another molecule in a direction favored by the electrochemical gradient.
		gradients are too high to be overcome by the energy generated in ATP hydrolysis.
		gradients and the relative concentrations of ATP, ADP and Pi.
	www.unc.edu /courses/pre2000fall/biol052/lectures/lecture7.html (935 words)

	nine (Site not responding. Last check: 2007-10-09)
		In other works, it would move from the area of high concentration (the spot where the salt was poured), to the areas of low concentration (the rest of the water).
		While solute can move against the concentration gradient (to the left), much more of it is diffusing into the side with a lower concentration.
		Because of the concentration gradient of water, there will be a net movement of water to the right chamber.
	www.access.wvu.edu /class/bio4/nine.htm (433 words)

	Gradient. (Site not responding. Last check: 2007-10-09)
		Unless you unwisely chose a spot where the nutrient concentration doesn't increase noticably in any direction, the ball should start to move, only stopping when it either reaches a local concentration maximum, or it reaches a point where it can no longer detect much of a difference in concentration gradient in any given direction.
		Because the gradient is always perpendicular to the curves along which f(x,y) is constant, you should see it cross each of the constant value curves on the graph at pretty close to a right angle.
		As was mentioned previously, the paths the LOB follows may not be the most direct paths to local concentration maxima (they'll seldom be straight), but they're the best that evolution is likely to come up with.
	www.bio.brandeis.edu /biomath/populate/Contour.html (365 words)

	Re: Does active transport ONLY occur against a concentration gradient?
		Active transport is generally independent of the concentration gradient.
		Second, the concentration gradient will affect transport directly in the sense of simple mass action kinetics.
		I've greatly simplified this of course and a biophysics guru would raise their eyebrows I'm sure at my explanations, but for initial practical purposes, the concentration gradient does not have a major effect on the instantaneous activity of active transport systems.
	www.madsci.org /posts/archives/2004-08/1091816400.Cb.r.html (327 words)

	Chemotactic responses of Dictyostelium discoideum amoebae to a cyclic AMP concentration gradient: evidence to support a ...
		Chemotactic responses of Dictyostelium discoideum amoebae to a cyclic AMP concentration gradient: evidence to support a spatial mechanism for sensing cyclic AMP -- Tani and Naitoh 202 (1): 1 -- Journal of Experimental Biology
		Chemotactic responses of Dictyostelium discoideum amoebae to a cyclic AMP concentration gradient: evidence to support a spatial mechanism for sensing cyclic AMP
		gradient irrespective of whether there was an increase or a decrease in the
	jeb.biologists.org /cgi/content/abstract/202/1/1 (323 words)

	Feasibility of using photophoresis to create a concentration gradient of solvated molecules (Site not responding. Last check: 2007-10-09)
		The objective of this work is to estimate the feasibility of creating a measurable concentration gradient of molecules in a solvent by a laser driven photophoresis process.
		The molecules are dissolved in a suitable solvent that is not significantly absorbing at the applied radiation frequency.
		The relevant physical parameters are estimated with the aid of molecular dynamics simulation methods on a prototype system, and the results indicate that a detectable concentration gradient may be established.
	www.cmm.upenn.edu /~moore/abs/abs_1.html (250 words)

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