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2013BIOAO2 Lecture 09.docx

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Biological Sciences
Ivana Stehlik

2013BIOAO2 S Module 1 January 7 ~Feb1 2013 Midterm date: Monday Febuary 4 2013. 5-7pm Module 2: Begins on Tuesday Feb 5 . th Total: 12 lectures Lecture outline: 1-2: Tree of life-plants 3-4 Plant cells and plant tissues 5-6. From seed to tree 7-8. From tree to seed 9. Transport in plants 10. Plant nutrition and soils 11. Plant defense 12. Plant life on the edge. Lecture 9 notes Transport in plants Basic plant needs: sugar=carbon dioxide + light +water, water, oxygen, minerals A) Water transport through xylem i) Hypotheses on mechanisms of water transport. How does water move through xylem? Answer: 3 hypotheses: capillary action, root osmotic push, transpiration. 1] capillary action- travels 1 m up xylem water move upward xylem through adhesion (water & tube walls) and cohesion (water & water molecutes). Adhesion is stronger than cohesion. Capillary action is not strong enough for trees because it travels for 1 meter! 2) Root osmotic push- travels 3 m up xylem Osmosis (osmotic pressure) is where water diffusion through semipermeable membrane such as the cell wall from a low concentration to a high concentration until both concentration are equal. Plant actively pump ions into root cells with ATP . water moves into cells by osmosis when oot hair have greater osmotic pressure (high ion_ than surrounding soil. But his only pushes the xylem by 3meters! 3) Transpiration-travels 100 +m up xylem. Use of cohesion. Sun turns liquid water into gas > gas moves from parenchyma into intercellular leaf space> cohesion pulls water from veins into parenchyma>gas diffuse out of stomata. ii) Synthesis, total plant water transport soil to root hair; osmosis into xylem: osmosis & transpiration pull (from leaves) up xylem between root and stem: transpiration root to leaves: cohesion angiosperms have more efficient trachieds and vessel elements-have perforation holes entering of water into roots:  Apoplastic transport:water flows through cell walls, more rapid, faster, less resistant to water flow  Symplastic transport: water flows through cell and pits of parenchymas.  Casparian strip: waxy layer that makes apoplastic transport impassable.  So it’s: root hair> epidermis>cortex> endodermis> Casparian strip> stele.(middle/vascular cambium)>xylem parenchyma>xylem vessels o Endodermis: control layer to what substances can enter xylem. o So when apoplastic cannot pass, they active transport into symplastic
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