Lecture 14 BIO 311D 2nd Edition Outline of Last Lecture I How plant cells specialize II How do plants grow Outline of Current Lecture I Review II How do plants exchange substances with their environment III Uptake into the roots Current Lecture I 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 Examples K 1 protons are pumped out 2 moves through a channel 3 Force electrical charge gradient NO3 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 cells Route 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 root
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