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Transportation (Concepts (Plants have only a few bascvic types of…
Transportation
Concepts
one fundamental aspect of life itself is the ability to transport specific substances to particular sits
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after death occurs atoms, ions and molecules diffuse moving from regions of higher concentration to regions of lower concentration #
Diffusion also occurs during life but proceeds more slowly that the controlled and oriented transport processes that tend to increase the order within the plant or animal body
transportation processes consume energy and many are driven by the exergonic breaking of ATP's high energy phosphate bonding orbitals
Specific transportation occurs at virtually every level of the biological organization: Enzymes transport electrons, protons and acetyl groups
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vascular tissues make it advantageous for shoots to grow upright, elevating leaves into the sunlight above competing plants
this elevation is feasible because photosynthetically produced sugars can be transported downward to other plants parts.
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Isolation mechanisms
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water Potential
Like any other chemical, water has a free energy, a capacity to do work
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because water is so important in botany, its chemical potential is usually referred as water potential
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water potential
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if water is under pressure, the pressure potential increases an does water potential
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most liquids can not be stretched very much, because water is cohesive
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Matric potential
water adhesion to dissolved structures such as the cells walls, membranes and soil particles
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Diffusion, osmosis and active transport
the first thing to consider is the mechanism by which materiel moves through a solution and crosses a membrane.
diffusion
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which random movement of particles in solutions causes them to move from areas where they are in relatively high concentration to areas where they are low concentrations
Osmosis
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Hydrophobic molecules diffuse easily through any cell membrane,
where as polar, hydrophilic molecules can cross differentially permeable membrane only if the membrane have special protein channels through which the molecules can diffuse
Aquaporins
water molecules, even through highly polar, pass through all memebrane
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molecular pumps
use energy of ATP to force molecules across the across the membrane, even if that type of molecules is extremely concentrated on the receiving side this is active transport
the molucule pump which in a protein, binds to both the molecule and ATP, then ATP splits into ADP and Phospate
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Intracellular transport
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during fusion, the membranes merge and the vesicle content are transferred into the organelle
cell and water movement
lysis
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even the thinnest most delicate walls of mature parenchyma cells can exert enough pressure on the protoplast to raise the pressure potential high enough to counterbalance osmotic potential #
immature growing cells have weak, deform able walls and cannot generate enough pressure to stop water absorption.
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under these conditions, the cell may increase greatly in size
with such a large influx of water, solutes in the cell may become significantly diluted
growing regions, such as the stem and roots
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guard cells
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the opening and closing of stomata pores are based on the S.D.I.T #
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when they must open, potassium are actively transported from surrounding cells into the guard cells
once inside the G. Cells, the potassium cannot leave because the plasma membrane is impermeable to it
the loss of potassium causes the water potential in adjacent cells to become less negative whereas absorption of potassium causes water potential in guard cells to become more negative. adjacent cells and guards cells are thrown out the hydraulic equilibrium #
the extra water and potassium causes the guard cell to swell bend and push apart opening opening the stomatal pore
Transfer cells
he rate which material can be actively transported depends on the number of molecules pumps present.
which in turn depends on the surface area of the plasma membrane: the larger the membrane, the more molecular pumps it can hold.
the walls are smooth on the outer surface but have numerous finger-like and ridge-like outgrowths on the inner surface
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the plasma membrane is pressed firmly against all of the convolutions and thus has consequently, the room is available for many molecular pumps and high-volume transport can occur across these transfer walls
cells are found in areas where rapid S.D.T is expected to occur. in glands that secrete salt , in areas that pass nutrients to embryos and in regions where sugar is loaded into or out of phloem #
Short distance Intracellular Transport #
Most plants communicate with their neighboring cells, transferring water, sugar, minerals and hormones
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motor cells
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the leaves of sensitive plants move slowly and reorient themselves by flexing and folding in response t a variety of stimuli
the location of flexure is either the entire midrib or the point at which the petiole attaches to the lamina or stem
motor cells
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are similar to guard cells: they can either accumulate or expel potassium and thus adjust their water potential and turgidity
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