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The fluid dynamics of vascular transport in plants
Tomas Bohr
Department of Physics
Technical University of Denmark
Plants are among the most successful organisms on earth both in terms of total
biomass and individual size range. Contrary to animals, they lack the central organs
which we associate with life, such as heart or brain. This requires an efficient and
robust vascular system, which sustains growth and communication throughout the
entire organism, from root to leaf of even the tallest tree, and which can function
without a central heart to drive the sap. In the lecture I shall discuss the main
parts of the vascular system: the xylem transporting almost pure water, the phloem
transporting sugar solutions, with particular focus on the osmotically driven sugar
transport. The leaves are particularly interesting since they contain the outlets for
the xylem and the inlets for the phloem and thus control the entire flow. In the
seminar I shall show that it is possible to understand important structural features,
such as leaf sizes, on the basis of simple fluid dynamical considerations, but that
several important questions remain unanswered.
osmosis
evaporation
photosynthesis
mesophyll
phloem
loading
sugar
unloading
phloem
xylem