Passive transport - wikipedia Passive transport This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. ( September 2016 ) 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. The four main kinds of passive transport are simple diffusion, facilitated diffusion, filtration, and / or osmosis. Contents 1 Diffusion 2 Facilitated diffusion 3 Filtration 4 Osmosis 5 See also 6 References Diffusion Main article : Diffusion Passive diffusion on a cell membrane. Diffusion is the net movement of material from an area of high concentration 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 materials from an area of higher concentration to an area of lower concentration, 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 '' ). 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 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. 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. Facilitated diffusion Main article : Facilitated diffusion 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. Filtration Main articles : Filtration and Ultrafiltration ( renal ) 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 albumins, 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, but not forgetting cells are extremely small to allow a variety of solutes to pass through and be metabolized. Osmosis Main articles : Osmosis and Tonicity Effect of osmosis on blood cells under different solutions. Osmosis is the movement of water molecules across a selectively permeable membrane. The net movement of water molecules through a partially permeable membrane from a solution of high water potential to an area of low water potential. A cell with a less negative water potential will draw in water but this depends on other factors as well such as solute potential ( pressure in the cell e.g. solute molecules ) and pressure potential ( external pressure e.g. cell wall ). There are three types of Osmosis solutions : the isotonic solution, hypotonic solution, and hypertonic solution. Isotonic solution is when the extracellular solute concentration is balanced with the concentration inside the cell. In the Isotonic solution, the water molecules still moves between the solutions, but the rates are the same from both directions, thus the water movement is balanced between the inside of the cell as well as the outside of the cell. A hypotonic solution is when the solute concentration outside the cell is lower than the concentration inside the cell. In hypotonic solutions, the water moves into the cell, down its concentration gradient ( from higher to lower water concentrations ). That can cause the cell to swell. Cells that do n't have a cell wall, such as animal cells, could burst in this solution. A hypertonic solution is when the solute concentration is higher ( think of hyper - as high ) than the concentration inside the cell. In hypertonic solution, the water will move out, causing the cell to shrink. See also Active transport Transport phenomena References Jump up ^ Borbas, E. ; et al. ( 2016 ). `` Investigation and Mathematical Description of the Real Driving Force of Passive Transport of Drug Molecules from Supersaturated Solutions ''. Molecular Pharmaceutics. 13 : 3816 -- 3826. doi : 10.1021 / acs. molpharmaceut. 6b00613. CS1 maint : Explicit use of et al. ( link ) Jump up ^ Palmgren, Michael G. ( 2001 - 01 - 01 ). `` PLANT PLASMA MEMBRANE H+ - ATPases : Powerhouses for Nutrient Uptake ''. Annual Review of Plant Physiology and Plant Molecular Biology. 52 ( 1 ) : 817 -- 845. doi : 10.1146 / annurev. arplant. 52.1. 817. PMID 11337417. Jump up ^ Dreyer, Ingo ; Uozumi, Nobuyuki ( 2011 - 11 - 01 ). `` Potassium channels in plant cells ''. FEBS Journal. 278 ( 22 ) : 4293 -- 4303. doi : 10.1111 / j. 1742 - 4658.2011. 08371. x. ISSN 1742 - 4658. Alcamo, I. Edward ( 1997 ). `` Chapter 2 -- 5 : Passive transport ''. Biology coloring workbook. Illustrations by John Bergdahl. New York : Random House. pp. 24 -- 25. ISBN 9780679778844. Sadava, David ; H. Craig Heller ; Gordon H. Orians ; William K. Purves ; David M. Hillis ( 2007 ). `` What are the passive processes of membrane transport ? ''. Life : the science of biology ( 8th ed. ). Sunderland, MA : Sinauer Associates. pp. 105 -- 110. ISBN 9780716776710. Srivastava, P.K. ( 2005 ). Elementary biophysics : an introduction. Harrow : Alpha Science Internat. pp. 140 -- 148. ISBN 9781842651933. Membrane transport Mechanisms for chemical transport through biological membranes Passive transport Simple diffusion ( or non-mediated transport ) Facilitated diffusion Osmosis Channels Carriers Active transport Uniporter Symporter Antiporter Primary active transport Secondary active transport Cytosis Endocytosis Efferocytosis Non-specific, adsorptive pinocytosis Phagocytosis Pinocytosis Potocytosis Receptor - mediated endocytosis Transcytosis Exocytosis Degranulation Retrieved from `` https://en.wikipedia.org/w/index.php?title=Passive_transport&oldid=862160435 '' Categories : Transport phenomena Cellular processes Membrane biology Physiology Hidden categories : CS1 maint : Explicit use of et al. 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Question: passive movement of a solute by carrier protein is called
Answer: Diffusion