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Lecture 17

Lecture 17 - Water and Nutrient Absorption I

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Western University
Biology 2601A/B
Graeme Taylor

LECTURE 17 – WATER AND NUTRIENT ABSORPTION I: ROOT STRUCTURE AND FUNCTION Cohesion-Tension Theory  Water is pulled from soil into roots and up to leaves  Negative water potential generated at the mesophyll cell wall  As water evaporates through pores, creation of negative water potential which in turn, propagates down the xylem  Cohesion of water molecules (hydrogen bonding) transfers tension down the water column  Water is pulled up towards the site of evaporation  Water is transported by the xylem How Does Water get into the Plant?  Root network is much more extensive than the above ground component of the plant  At the apex, root is covered in mucigel sheath which acts to protect the tip of the root o “Root lubricant”  Quiescent center – cells do not develop until needed  Region of rapid cell division – where root is actively growing, pushes root downwards  Epidermis – skin layer  Endodermis – inner skin o Has a Casparian strip  Vascular tissue is located in the center of the root, together they are known as the stele  Meristem – part of the pant that continues to divide and grow  Root hair zone – vast majority of nutrients and water are being taken up by the root in this area  Suberin – waxy substance that is waterproof o Roots are suberized in certain parts of the root tissue o Not a lot of suberization at the tip of the root because this is where water needs to be absorbed so it cannot be sealed from the environment Root Cap  Directs growth and senses the environment  Growth is towards: o Gravity – amyloplasts sediment in columella cells  Columella cells – highly specialized, statolith can be found inside which are basically big granules of starch that fall with gravity  This is how plants recognize which side is “down”
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