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BIO Exam 2 - Stack 4

Resource Acquisition and Transport in Vascular Plants

Adaptations for ___ were key steps in the evolution of vascular plants. acquiring resources
___ drives the transport of water and minerals from roots to shoots via the xylem. Transpiration
Sugars are transported from ___ to ___ via the phloem. - sources - sinks
How do water and minerals get into the root cells in the first place? - the epidermal cells of root tips are permeable to water, and many are differentiated into root hairs - root hairs absorb soil solution - soil solution is drawn into the hydrophilic walls of the epidermal cells
Once in, how do water and minerals get into the xylem (which is in the center of the root)? via the apoplastic or symplastic route
Explain the apoplastic route. - soil solution makes its way thru the apoplast of a root hair cell and epidermal and cortical cells - passes thru casparian strip of endodermis (filtered at this point) - enters vessels in vascular cylinder and is transported up the plant
Explain the symplastic route. - soil solution passes thru plasma membrane of root hair (filtered at this point) - travels thru symplast of epidermal and cortical cells - passes thru casparian strip of endodermis - enters vessels in vascular cylinder and is transported up the plant
What is the function of the endodermis? - it is the last checkpoint for the selective passage of minerals from the cortex into the vascular cylinder - just like plasma membrane, it functions as a filter, however, both routes MUST pass through it
Casparian strip a water impermeable ring of wax in the endodermal cells of plants that blocks the passive flow of water and solutes into the stele by way of cell walls
stele the central core of the stem and root of a vascular plant, consisting of the vascular tissue (xylem and phloem) and associated supporting tissue
xylem sap the water and dissolved minerals in the xylem
transpiration the evaporative loss of water from a plant through stomata
The xylem sap is mainly ___ upward. pulled
What is root pressure and how does root pressure develop? - pressure exerted in the roots of plants as the result of osmosis - root cells actively pump minerals into xylem - casparian strip prevents them from leaving - this makes the rel. conc. of water inside the plant lower than the outside, so it comes in
guttation - root pressure sometimes causes more water to enter the leaves than is transpired -> guttation - the exudation of water on the tips or edges of some plant leaves
Why is root pressure alone not sufficient for getting xylem sap to the top of most plants? - the positive pressures produced are too weak to overcome the gravitational force of the water column in the xylem (particularly in tall plants) - some plants don't even generate root pressure
cohesion-tension hypothesis - the leading explanation of the ascent of xylem sap - states that transpiration exerts a pull on xylem sap, putting it under negative pressure - the cohesion of H2O molecules transmit this pull along the entire length of the xylem (shoots to roots)
cohesion - the linking together of like molecules, often by hydrogen bonds - or, the attractive force between molecules of the same substance (ex. water)
Explain why H2O molecules stick together. - polar covalent bond between O and H2 creates a partially neg. charge around the O and a partially pos. charge at the H (b/c O is more electroneg.) - partially neg. O's are attracted to partially pos. H's of other molecules of water -> hydrogen bonds
transpiration - evaporation of water from stomata in plant leaves - a pulling process
adhesion - the attractive force between water molecules and other polar substances (ex. cellulose molecules in the xylem cell walls) - offsets the downward force of gravity
Why does water evaporate from leaves? - the concentration of water is highest in the air spaces of leaves and lowest in the dry air outside - so, when stomata are open, water automatically diffuses = transpiration - high concentration -> low concentration
How does loss of water vapor from the leaf translate into a pulling force for upward movement of water through a plant? - cohesion of water makes it possible to pull up a column of xylem sap w/o the molecules separating - H2O exiting the xylem in the leaf tug on adjacent H2O, and this pull is relayed, molecule by molecule, down the entire column of water in the xylem
translocation the transport of organic nutrients (mostly sucrose) in the phloem of vascular plants
phloem sap - the sugar-rich solution carried through a plant's sieve tubes (can also contain amino acids, hormones, and minerals) - like maple syrup
What is the direction of translocation compared to the direction of water/mineral transport? - moves from sites of sugar production to sites of sugar use or storage - SOURCE TO SINK
How does sucrose get from photosynthetic cells in the leaves to the phloem? (A mesophyll cell is a type of parenchyma cell.) - sucrose must be transported into sieve tube elements before being exported to sugar sinks - apoplastic and symplastic routes - active transport can be used
How does sucrose get from a sugar source to a sugar sink? What is bulk flow by the creation of positive pressure? - the phloem sap moves through sieve tubes by bulk flow driven by positive pressure - the building of pressure at the source and reduction of that pressure at the sink cause sap to flow from source to sink
What are the four basic steps of the bulk flow of phloem? - loading of sugar (active transport) - uptake of water (osmosis, xylem -> phloem) - unloading of sugar (pressure relief) - recycling of water (osmosis, phloem -> xylem)
Created by: jessica.gvc



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