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Transport in Vascular Plants (Xylem (Root Pressure (Water has a positive…
Transport in Vascular Plants
Xylem
Water enters through diffusion into leaves: water evaporates from inside of a leaf to outside through transpiration.
Root Pressure
Water has a positive pressure moving upwards, minerals are moved from soil into the xylem.
High concentration of materials lets water move in through osmosis letting positive pressure increase.
In high humidity, water can't evaporate.
Gutiation: high humidity, low rate of transpiration- fluid doesn't evaporate but forms tiny drops along side of the leaf.
Transpirational Pull
Cohesion-tension model explains how water is moved from roots to leaves.
Transpiration: caused from dry air, heat and wind-results in negative pressure exerting tension on the xylem tubes.
Cohesion: Attraction of water molecules to each other providing a force keeping its column unbroken.
Adhesion: Attraction of water molecules to xylem cell walls, keeping water column from breaking.
Phloem
Translocation: transportation of sucrose and organic molecules.
Pressure-Flow Model
Spongy mesophyll tissues and palisade are common sources.
Sinks= any region where sugars are used and stored.
Pressure-flow model: combination of osmosis and pressure dynamics through translocation.
Two bulbs = connected, end are each covered by a selectively permeable membrane letting only water pass.
First tube= higher concentration, lets water flow into it creating a pressure difference.
When pressure builds in second, water diffuses out, flow stops when sucrose levels are equal.
Pressure Flow
When nutrients = pumped/removed, change in concentration lets water move in the same direction.
Builds up internal pressure at the source end pushing sucrose rich solution to any sink where sucrose is removed.
Direction of flow = always source to sink.