Mass flow - wikipedia Mass flow This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( December 2009 ) This article is about the flow of fluids in biological systems. For use of mass flow in physics see Fluid Dynamics. For bulk flow in physics see Advection. For protein transport in cell biology see Bulk movement. Mass flow, also known as `` mass transfer '' and `` bulk flow '', is the movement of fluids down a pressure or temperature gradient, particularly in the life sciences. As such, mass flow is a subject of study in both fluid dynamics and biology. Examples of mass flow include blood circulation and transport of water in vascular plant tissues. Mass flow is not to be confused with diffusion which depends on concentration gradients within a medium rather than pressure gradients of the medium itself. Contents 1 Plant Biology 1.1 Xylem 1.2 Phloem 2 See also 3 References Plant biology In general, bulk flow in plant biology typically refers to the movement of water from the soil up through the plant to the leaf tissue, but can also be applied to the transport of larger solutes ( e.g. sucrose ) through the phloem. Xylem According to cohesion - tension theory, water transport in xylem relies upon the cohesion of water molecules to each other and adhesion to the vessel 's wall via hydrogen bonding combined with the high water pressure of the plant 's substrate and low pressure of the extreme tissues ( usually leaves ). As in blood circulation in animals, ( gas ) embolisms may form within one or more xylem vessels of a plant. If an air bubble forms, the upward flow of xylem water will stop because the pressure difference in the vessel can not be transmitted. Once these embolisms are nucleated, the remaining water in the capillaries begins to turn to water vapor. When these bubbles form rapidly by cavitation, the `` snapping '' sound can be used to measure the rate of cavitation within the plant. Plants do, however, have physiological mechanisms to reestablish the capillary action within their cells. Phloem Solute flow is driven by a difference in hydraulic pressure created from the unloading of solutes in the sink tissues. 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. See also Countercurrent exchange Pounds Per Hour Fluid Dynamics Mass flow rate Hemorheology Flying and gliding animals References Jump up ^ Moyes & Schulte ( 2008 ). Principles of Animal Physiology. Pearson Benjamin Cummings. San Francisc, CA. Jump up ^ Taiz, Lincoln ; Zeiger, Eduardo ; Moller, Ian Max ; Murphy, Angus ( 2015 ). Plant Physiology and Development. Sunderland, MA : Sinauer Associates, Inc. p. 66. ISBN 978 - 1605353531. Jump up ^ Pockman, W.T., Sperry, J.S., & O'Leary, J.W. 1995. Sustained and significant negative water pressure in xylem. ' Nature ' 378 : 715 - 716 Jump up ^ Lambers, Hans ( 2008 ). Plant Physiological Ecology. 233 Spring Street, New York, NY : Springer Science + Business Media, LLC. p. 153. ISBN 978 - 0 - 387 - 78341 - 3. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Mass_flow&oldid=787255002 '' Categories : Fluid dynamics Hidden categories : Articles needing additional references from December 2009 All articles needing additional references Wikipedia articles needing clarification from August 2016 All articles with specifically marked weasel - worded phrases Articles with specifically marked weasel - worded phrases from August 2016 All articles with unsourced statements Articles with unsourced statements from August 2016 Talk Contents About Wikipedia Català Gaelg Português Türkçe Tiếng Việt Edit links This page was last edited on 24 June 2017, at 10 : 19. About Wikipedia

Question: the movement of water in the xylem relies upon the
Answer: cohesion of water molecules to each other and adhesion to the vessel's wall via hydrogen bonding combined with the high water pressure of the plant's substrate and low pressure of the extreme tissues (usually leaves)