Bio Lecture #6

Bio Lecture #6 - Bio Lecture #6 Xylem- tracheary elements...

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Bio Lecture #6 Xylem- tracheary elements Thick lignified secondary walls (still has cellulose) Pits and pit pairs Long Distance (LD) via transpiration-cohesion-tension mechanism H 2 O is pulled up Driven by transpiration Water is cohesive Creates strong tension Driven by ψ gradient Airψ= -100 MPa Leaf airψ= -7.0 MPa Leaf cell walls= -1.0 MPa Xylem ψ= -0.8 MPa Root ψ= -0.6 MPa Soil ψ=-0.3 MPa As goes down the tree the ψ goes down. 2 regions for generating tension 1. Stomata- air a. Open during the day b. Transpiration: loss of H 2 O from leaf 2. Air Spaces a. Evaporation: vaporization of H 2 O (liquid to gas) #1. Stomata – Air Transpiration= water out of leaf Loss of H 2 O vapor From higher ψ to lower ψ #2. Air Space Transpiration encourages evaporation from cells ( think of cells as wicks) More evaporation= more surface tension (decrease ψ p ) The driving force in moving water: Transpiration: loss of H 2 O Stomata Transpiration causes tension Transpiration ↑ evap ↑ surface tension ↓ψ
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Bio Lecture #6 - Bio Lecture #6 Xylem- tracheary elements...

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