Akond, Harun .
Molecular theory of water transport in plants and the transpiration-pull.
Plants need water and they collect it from soil via roots. The mystery of plants world is the mechanism of water uptake against strong gravitational force. There are several hypotheses; however, transpiration-pull is the most popular one. But this great hypothesis fails to explain the mechanism. It is believed that strong cohesive force between water molecules makes water column, even more than 350 ft high in xylem capillary tube, a string stronger than a steel rod. This wrong concept directed the hypothesis towards a black hole. This molecular theory explains the hypothesis in micro level using laws of physics and gets rid of black hole. A tiny volume surrounded by epidermis and parenchyma behaves as a heartlet and the surrounded air space behaves as chamber. The transpiration starts when a heartlet systoles by parenchyma. This systole pumped out a tiny drop of water through stoma and then closed by the guard cells. Then heartlet slowly starts diastole by parenchyma and produces huge negative (inward) pressure in the chamber. Heartlets have narrow passage towards vein which connects xylems. Local pressure gradient between a heartlet and a xylem helps to opens near end of the capillary tube and closes far end. As a result, a very small amount of water flows from xylem to heartlet to keep isobaric equilibrium. But it produces pressure gradient with the adjacent xylem and kisses to maintain isobaric equilibrium. Isobaric equilibrium between two xylems (or xylem and heartlet) and pressure gradient to the far ends force to stop kissing other ends. These process forms a digital kissing system of two ends of a capillary tube of xylem which starts from leaf and ends at root causes upward flow of water and its solutes. The frequency of kissing of xylems depends on the plantís needs of water.
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1 - University of Chittagong, Physics, Campus, Chittagong, 4331, Bangladesh
xylem structure and function
local pressure gradient
digital kissing system
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 11:30 AM