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This article is about the flow of fluids in biological systems. For use in physics see Fluid Dynamics. For use in cell biology (i.e. protein transport within a cell) see Bulk Flow.
Mass flow, also known as “mass transfer” and “bulk flow”, is the movement of fluids down a pressure or temperature gradient [1], 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. Diffusion, in contrast, depends on concentration gradients, distinguishing it from mass flow.
Physical considerations
editConservation of mass, momentum, and energy
editBernoulli’s equation
editReynold’s number
editGravity
editCauses of pressure gradients in biological systems
editin Animal Biology
editLocomotion
editStokes flow – slime molds – colonies as fluids
Cell motility – Low Reynolds number
Large animal motility – High Reynolds number (squids, whales, fishes)
Secretion of glandular products
editCirculatory systems – Hemorheology
editLymphatic system
editExcretory system
editDigestive systems
editEsophagus
Intestines
Water flow in sea stars, sea cucumbers, sponges
editRespiration
editIn water In air
Plant Biology
editIn 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
editAccording 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).[2]
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 cannot be transmitted. Once these embolisms are nucleated [definition needed], 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 .[3] Plants[which?] do, however, have physiological mechanisms to reestablish the capillary action within their cells [clarification needed][citation needed].
Phloem
editSolute flow is driven by a difference in hydraulic pressure created from the unloading of solutes in the sink tissues.[4] 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
editReferences
edit- ^ Moyes & Schulte. Principles of Animal Physiology.
- ^ Taiz, Lincoln; Zeiger, Eduardo; Moller, Ian Max; Murphy, Angus (2015). Plant Physiology and Development. Sunderland, MA: Sinauer Associates, Inc. p. 66. ISBN 978-1605353531.
- ^ Pockman, W.T., Sperry, J.S., & O'Leary, J.W. 1995. Sustained and significant negative water pressure in xylem. 'Nature' 378: 715-716
- ^ 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.