BIO-0014 Lecture 14: Movement of Sugars through the Phloem

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1. Hydraulic redistribution
a.
i. Higher water potential near the base of the tree
1. Heavy isotope percentage was high at 57% signaling it was
pulling water deep from underground
ii. Dryer as you move further away from the tree
1. Heavy isotope percentage was low at 25% signaling the meadow
was mostly getting its water from precipitation
iii. More humid under then tree than out in the open
b. Hydraulic redistribution: Water movement from moist to dry soil layers using roots
as conduits
i.
1. Not only lifting water deep underground and bringing it into the
atmosphere
2. But also redistributing to the soil around it due to leaking
3. Some plants can only grow next to the tree because of the heavy
isotope water
a. Tree provides hydraulically redistributed water
b. Special types of plants can be found under strategically
placed trees
ii. Continually advanced theory
1. Originally thought trees only brought up water from underground
into the atmosphere
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2. Scientists realized that trees can also redistribute water to the soil
around it
3. By watering the soil around it, allows species to grow around it
a. Called hydraulic parasites by some scientists since they
take water away from the tree and the area around it
2. Phloem
a. Location and architecture
i.
ii. Xylem cells are dead
1. Thick, rigid, cell walls
2. Water flows through them
3. Under tension
iii. Phloem cells are living
1. Moves sugar through them
2. Located right next to them near the outside
3. The bark of trees is where phloem is located
4.
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