Mass Transport in Plants

• Describe the cohesion-tension theory of water transport in the xylem (5)

  1- water lost from leaf due to transpiration

  2- lower water potential of mesophyl / leaf cells

  3- water pulled up xylem (creating tension)

  4- water molecules cohere / stick together by hydrogen bonds

  5- forming a continuous water column

  6- adhesion of water molecules to walls of xylem
• Mass Flow Model

  1- sucrose activley transported int the phloem

  2- by companion cells

  3- this decreases water potential of the phloem and water enters by osmosis

  4- produces a hydrostatic pressure gradient

  5- so we get mass flow to the active transport

  6- sucrose unloaded via active transport

  7- water moves back into the xylem by osmosis
• Lignin structure to function

  strengthens and thickens wall to prevent collapse of xylem waterproofing to reduce loss of water imporve adhesion of water molecules - increase capiliarity spiral for flexibility - prevents stem breaking