Navigation Links
Passive transport


Passive transport is a means of moving biochemicals, and other atomic or molecular substances, across membranes. Unlike active transport, this process does not involve chemical energy. Passive transport is dependent on the permeability of the cell membrane, which, in turn, is dependent on the organization and characteristics of the membrane lipids and proteins. The four main kind of passive transport are diffusion, facilitated diffusion, filtration and osmosis.

Contents

Diffusion

Main article: Diffusion

Diffusion is the net movement of material from an area of high concentration of that material to an area with lower concentration. 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").

If and when the concentration gradient have been eliminated, no net exchange of material occurs. Although material may move forth from one area to the other, it will be balanced by movement of the same amount of material to the opposite direction.

Diffusion is biologically important because it enables the abolishment of concentration gradients in the body. For example, metabolic activity will consume oxygen, which will reduce its concentration in the bloodstream; diffusion of oxygen in the alveoli of the lungs allows it to be replenished.

Facilitated diffusion

Main article: Facilitated diffusion

Facilitated diffusion is movement of molecules across the cell membrane via special carrier proteins that are embedded within the cellular membrane. A lot of large molecules, such as glucose, are insoluble in lipids and too large to fit through the membrane pores. Therefore, it will bind with its specific carrier proteins, and the complex will then be bonded to a receptor site and moved through the cellular membrane. Bear in mind, however, that facilitated diffusion is a passive process, and the solutes still move down the concentration gradient.

Filtration

Main article: Filtration

Filtration is movement of water and solute molecules across the cell membrane due to hydrostatic pressure generated by the cardiovascular system. Depending on the size of the membrane pores, only solutes of a certain size may pass through it. For example, the membrane pores of the Bowman's capsule in the kidneys are very small, and only albumin, the smallest of the proteins, have any chance of being filtered through. On the other hand, the membrane pores of liver cells are extremely large, to allow a veriety of solutes to pass through and be metabolized.

Osmosis

Main article: Osmosis

Osmosis is basically diffusion of water molecules. Most cell membranes are permeable to water, and since the diffusion of water plays such an important role in the biological functioning of any living being, a special term has been coined for it -- osmosis.

Water molecules "stick" together via weak hydrogen bonds; therefore, unlike most solutes, water molecules move around in large clumps, a phenomenon known as bulk flow.


'"/>


(Date:12/10/2014)... DIEGO , Dec. 9, 2014 CIE ... collaboration catalyst that provides the connective tissue that enhances ... enabling them to easily share client-level information; earned a ... to expand to organizations serving seniors aging in community ... Diego" partner on December 11 th 4-6p. ...
(Date:12/5/2014)... Dec. 4, 2014 Increased emphasis on ... in new testing and inspection technologies. The convergence ... to a range of innovative test solutions. This ... Generation Y, which is generally more inclined towards ... product development strategies of test equipment vendors will ...
(Date:12/3/2014)... , Dec. 2, 2014   Marvin ... deployed, innovative test solutions for military, aerospace, and ... version of its successful TS-900 PXI semiconductor ... and features of high-end systems to customers at ... value compared to traditional ATE. ...
Breaking Biology News(10 mins):Community Information Exchange San Diego Launches Pilot, Secures $1 Million Expansion Grant, and Becomes a "Live Well San Diego" Partner 2Community Information Exchange San Diego Launches Pilot, Secures $1 Million Expansion Grant, and Becomes a "Live Well San Diego" Partner 3Community Information Exchange San Diego Launches Pilot, Secures $1 Million Expansion Grant, and Becomes a "Live Well San Diego" Partner 4Emerging Technologies Enable Smarter Monitoring of Assets, Push Industrial Testing, Inspection and Monitoring Market 2Emerging Technologies Enable Smarter Monitoring of Assets, Push Industrial Testing, Inspection and Monitoring Market 3Emerging Technologies Enable Smarter Monitoring of Assets, Push Industrial Testing, Inspection and Monitoring Market 4Marvin Test Solutions Brings New Capabilities to PXI-Based Semiconductor Test with TS-960 2Marvin Test Solutions Brings New Capabilities to PXI-Based Semiconductor Test with TS-960 3
... and students will come together at the Fine Conference ... Mellon University to explore how science research and education ... large digital images containing billions of pixels. , Alan ... Worden, director of NASA,s Ames Research Center, and Mark ...
... to be presented at the EORTC-NCI-AACR [1] Symposium on "Molecular targets ... meeting at 00.01 hrs CET on Friday 29 October. The Symposium ... to report on the online abstracts from the time that they ... mind that all the abstracts had to be submitted by 15 ...
... in French . Quebec City, October ... death of pancreatic cells and could increase the risk of ... Laval,s Faculty of Pharmacy. Details of this discovery were recently ... . In vitro tests conducted by Professor Frdric Picard ...
Cached Biology News:'Science never seen before' is focus of first scientific conference on gigapixel imaging 2Abstracts for the EORTC-NCI-AACR Symposium in Berlin go up online on Friday, Oct. 29 2Glucosamine causes the death of pancreatic cells 2
Other biology definitionOther Tags