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Bio Final

rename
Updated 2007-06-11 13:41
Question Answer
water potential-the potential energy that water has in an environment compared to pot energy of pure water at same temp and pressure
how is water potential important to plants?it determines the direction of water movement from roots to shoots because roots have a higher water potential
The water potential equation&w = &s + &p
&srefers to the concentration of solutes and the more you have the more negative the term becomes
&prefers to the hydrostatic pressure
what are the two types of &p?1.positive hydrostatic pressure which is turgor pressure and 2. negative hydrostatic pressure which is tension
why don't cells burst if too hypotonic in plants?the plasma membrane pushes on the rigid cell wall and cell wall pushes back
turgor pressure-as water moves into the cell the pressure inside the cell is called this and it counteracts movement of water due to osmosis
what causes wilting?when tissue loses turgor
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Question Answer
Tensionthe act of being stretched or strained
surface tensionthe pull that exists on water molecules at an air-water interface
meniscus-concave boundary layer that forms because of hydrogen bonding
why is a miniscus formed?there are hyrogen bonds everywhere in water, but on the surface the only hydrogen bonds that can be made are underneath them and it pulls them down
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Question Answer
what are the two major components of tension?cohesion and adhesion
cohesion-tendency of H2O molecules to stick together which needs a lot of energy to push them apart. It creates a downward tension which pushes water molecules up
adhesion-the molecular force of attraction in the area of contact between unlike bodies that acts to hold them together. It adheres off cell wall and coheres with each other
water adhesion example-when a water droplet interacts with a hydrophobic film like wax, the water pulls together and do not interact with air
cohesion bonds are strong because.each molecule can have 4 different bonds; 2 on the oxygen and one on each hydrogen
what kind of bonds do water molecules form?hydrogen bonds
syringe example-syringe filled with air and finger blocking the suction when pulled still gives and goes back because air molecules are expansive not cohesive...but when water is in the syringe and the suction is blocked it doesn't give because water is cohesive
can par cells withstand tension?no,if h2o comes out of the cell, then &p=0 and the plant wilts and dies (alive)
which cells can withstand tension?tracheids and vessel elements because it has a strong, lignified secondary cell wall. (dead cell: all other living cells would collapse)
transpiration-loss of water in vapor form which takes place through the stomata
why do plants lose h2o?it needs to lose h2o so that co2 can come in for photosynthesis
apoplastic-movement of water molecules outside of living cell or inside dead cells not through protoplasm or across membranes
symplastic-path of water cell to cell through plasmodesmata
where must symplastic transportation of water occur?endodermis because casperian strip is there blocking apoplastic pathway with suberin (waxy layer)
where is there only diffusion in water movement?from cortex to endoderm and from endoderm to xylem
how does water get into endodermis?via proteins (aquaporins)
three important facts about the endodermis1.reduces potential for getting through small bubbles in vessels 2. acts as a gate that regulates what minerals go into vessels 3.reduces calvitation
calvitation-in regions of low pressure, the break in the water column and as the air pocket expands it compromises with water flow
guttation-loss of water in liquid form when water moves up xylem and into leaves at a faster rate that transpiration is occuring. (forced out by root pressure)
2 factors for transpiration to occur.1.open stomata 2. air surrounding leaves is drier than air inside leaves (atomospheric humidity less than 100%)
what must happen if guttation occurs?stops transpiration
mass flow-movement of nutrients through phloem
how do sugars move?translocation...from sources to sinks (usually from leaves to sinks like roots or fruit cell)
sinka tissue where sugar exits the phloem with low concentration of sugar
sourcea tissue where sugar enters the phloem with a high concentration of sugar
What happens in translocation?mesophyll leaf cells make sucrose, which leave through companion cells into the sieve tube elements causing high &s which makes water from the xylem flow in which increases turgor pressure that causes movement down towards the sink. Sucrose is unloaded by active transport and water then flows back into xylem.
what effects translocation?more photosynthesis/higher temp = faster rate
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Question Answer
1st law of thermodynamicstotal energy remains constant
2nd law of thermodynamicsall things seek lower state of free energy
low entropy =more order and more energy input
absolute zeroall molecular motion stops but can't ever reach it...at a specific point molecules have a direction but over a long period they don't
diffusionnet directional movement of particles that seek lower free energy (G) state.
diffusion rate are influenced bydistance... change in free energy gradient, S.A, Resistance
when SA goes up... diffusion rate goes up
when resistance goes updiffusion rate goes down
change in free energy gradient is higherthe diffusion rate is higher
diffusion is slower over...long distances
free energy goes up if these factors go upconcentration, temperature, pressure, charge separation
increase in temp and hydrostatic pressure...increase water potential
increase in solutes...decreases water potential
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