BIOL 1106 – Lesson 3 – 1/27

1. In the spring the sap in maple trees flows up the tree through the xylem by the water potential difference from root > stems. 2. How does water move into xylem? a. Epidermis > across Root Cortex > Regulated by asparian Strip > finally in the Stele (vascular bundle) b. Examples of dissolved solutes: i. Nitrate ii. Phosphate iii. Sulfate c. Related terms: iv. Transpiration v. Adhesion and cohesion vi. Water potential – predicts and calculates which way water flows 1. Water Potential is a measure of potential energy that predicts which way water will move 3. Calculating water potential d. Water potential = pressure potential + solute potential vii. Pressure potential – pressure exerted by the plant cell wall that limits water from moving in viii. Solute potential – the effect of solute concentration. Pure water at atmospheric pressure has a solute potential of zero. As solute is added, the value for solute potential becomes more negative. e. Potential energy to move by diffusion osmosis across membranes f. Water moves from an area of lower to high solute concentration g. Water moves from an area of high water potential to low water potential h. Pure water has a psi of zero; that value decreases with additional solutes, and how much the cell walls/membranes “push” back i. As water evaporates, the cells in the leaves loose water and have higher solutes concentration. j. Water potential decreases as you go from roots to leaves; so water wants to keep moving up the xylem toward that lower water potential k. Cohesion-tension – stomata are tiny allowing surface tension to maintain the water/air boundary; so water is continually on the move by osmosis into the root hair and up the stems 4. Water and mineral transport l. Root hair epidermis greatly increases absorptive surface area, so do their symbiotic mycorrhizae 5. Guard cells m. Hormones: Malate (open stoma) and ABA (close stoma) n. Guard cell turgor pressure is regulated by K, Cl, malate, and ABA o. When guard cells are turgid, stomata are open p. Generally, stomata are open during the day and closed at night q. In some plants, stomata open only when it is not too dry (or at night) 6. Translocation through phloem r. Pressure-flow ix. Dissolved organix solutes like sucrose and hormones are translocated throughout the plant in phloem x. Translocation is accomplished aong concentration gradients xi. The plant sets up gradients through source and sink 2. Source – where it’s made 3. Sink – where it’s used/stored 4. Or source, sink; where it’s stored, where it’s needed 7. Plant adaptations to water stress s. C4 t. Waxy cuticle u. Hairy leaves v. Tiny or no leaves w. Wilting x. Dormancy/deciduous