Lecture 14 BIO 311D 2nd EditionOutline of Last Lecture I. How plant cells specializeII. How do plants grow?Outline of Current Lecture I. ReviewII. How do plants exchange substances with their environment?III. Uptake into the rootsCurrent LectureI. Review- Growth of a root: cell division, cell elongation, cell maturation- Vascular tissue: cells specialized for transport: Xylem vessels (various shapes): mature dead cells Phloem: sieve tube element (nucleus disintegrates + big vacuole), companion cell (DD)II. How do plants exchange substances with their environment?- Leaf: absorb CO2, take in sunlight (solar energy)- Roots: take in water- Exchange between plant and soil:- How can plant take up water? – water follows solutes - Uptake of solutes against their concentration gradients? – First, build a proton gradient - How do potassium enter cell, against their concentration gradient?- How do negative ions like NO3- enter cell?- Always ask: (1) what transport protein is involved? (2) What is source of energy/force?- Membrane potential and cation uptake, co transport of anions - ExamplesK+: (1) protons are pumped out, (2) moves through a channel, (3) Force: electrical charge gradientNO3-: (1) protons pumped outside, (2) symport or cotransport protein, (3) being transported the same time Hydrogen goes in - Water moves across membranes passively, by osmosis (either through phospholipid bilayer or aquaporin proteins)- Direction of movement depends on: (a) the concentration of solutes (osmotic pressure) and (b) physical pressure (fluid pressure, hydrostatic pressure) - Water potential is a measure of the ability of water to do work; water moves from high towards low water potential III. Uptake into the roots- When the solute concentration is higher inside the root hair cell than outside it, the flow of water through the membrane tends to be move into root hair cell [water follows solutes]- When the fluid pressure is higher inside the root hair cell than outside it, the flow of water will tend to move out of the root hair cell or could possibly have no net movement. - Transport of water from soil to root to xylem, passive depends on pressure flow going up to a point - Casparian strip is a way belt around the wall of endodermis cellsRoute: (1) symplastic (inside the cell membrane), (2) apoplastic (in the cell walls)Function of the strip: causes selective entry of water and solutes into center of
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