HIST10014 Lecture Notes - Lecture 10: Xylem, Root, Phloem
6 Aug 2018
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Document Summary
Uptake and loss of water were not an issue. Plant evolution is about adaptation to a terrestrial environment. Primitive land plants have no conducting tissues or roots. Plants need a conducting system as small molecule di use about 50 micrometers in 1. Molecules that di uses across cell in 1 second requires 8 years to di use 1 metre. Cytoplasmic streaming increases this to 5cm per hour (okay for large laval cells) Most abundant compound in plant cells (85-95% fresh weight) 70% of a human body is made up of a water. 95% of water fathered is lost to the atmosphere often within a few hours. Internal leaf surface up to 200x external surface. Replaced by water taken up by roots (xylem) Water moves through plant up to 75cm per minute. When the transpiration rate is very low, root xylem sap may be under positive pressure. Wind increases the transpiration rate by decreasing the thickness of this boundary layer.
