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43 Cards in this Set
- Front
- Back
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Water potential
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Is the measure of the free energy of water.
Water always moves from high --> low potential |
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Water potential of pure water vs. water that is not pure
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pure = 0
impure < 0 |
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Equation for water potential
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Ψ = π + p
water potential = osmotic potential + pressure |
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Describe gradient of water movement
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Water moves along a gradient of decreasing potential
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How does adding solutes to water affect the osmotic potential?
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Adding solutes to water decreases (more negative) osmotic potential
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How does reverse osmosis work?
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Apply a pressure greater than the osmotic potential to make pure water on the other side of the membrane
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How are plant cells able to handle higher pressures?
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Because their cell walls are stiff enough to not break when pressure is applied
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In trees, what component is required for water transport? What component is not required?
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Living leaves are required for water transport, but living cells are not required (water can be transported through xylem or phloem.)
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What are the 3 components of the Cohesion-Tension Theory?
What do (-)ive and (+)ive number mean? |
1) Driving Force (gradient from soil to roots to stem to leaves to air.)
2) Hydration in the pathway 3) Cohesion of Water (-)ive numbers mean "tension" (+)ive numbers mean "pressure" |
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What is transpiration?
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Where water readily evaporates from leaves
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What is embolism or cavitation?
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If the water pathway doesn't stay hydrated and air gets in, the pathways will break.
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Describe pressure in the xylem
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The xylem is dead, so it has great negative pressures. It is under "tension."
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Why/How does a Christmas tree take up water after being transplanted if the bottom is cut in air?
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Cell walls retain water (paper towel roll) and will take up water through walls under great negative pressures. Water will then reinfiltrate the central xylem. There are also mechanisms to repair embolisms/cavitations.
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How does a mesophyll cell (that is alive) that needs positive pressure, get water from a source that has negative pressure?
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Because of osmosis, osmotic potential in mesophyll is VERY negative, which allows the pressure to stay positive. And water will move from higher to lower potential.
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In Drought Resistance, what is the difference between Adaptation and Acclimation?
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Adaptation is a genetic thing that is normally passed on.. Acclimation is a change in response to the environment at that time.
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What are the 3 categories of Drought Resistance?
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Avoidance- plant completes life cyle
Tolerance- have mechanisms to cope and will come back when environment is less harsh (resurrection fern) Postponement- This is Woody Plants! |
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What are the 6 major components of Drought Postponement?
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Root systems, leaf changes, stomatal changes, metabolic changes, water storage, osmotic adjustment.
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Describe changes in root systems for desiccation postponement
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Adaptation-- super deep root system
Acclimation-- trees of the same race grown in different regions may change the length of their root systems. |
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Describe changes in leaves for desiccation postponement.
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Size and Shape may change-- needles are better at dry climates
Waxy substances, or cuticles, may develop to keep water in, or more wax may be produced. |
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Describe osmotic adjustment for desiccation postponement
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active accumulation of solutes in response to a drought.
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How does water stress affect growth?
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Decresed Ps, cell division, cell elongation, and cell differentiation.
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What are growth regulators?
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Control growth and development in trees. Need a proper combination.
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What is the function of Auxin, the first identified growth hormone?
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Stimulates elongation of cells, encourages apical dominance, epicormic branching, phototropism (bending towards light-- auxin moves to shaded side), rooting of cuttings.
Auxin is produced in tree tops and flows downward! |
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How does Auxin work as a herbicide?
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Cause super-overgrowth until death.
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What is the function of Gibberellins?
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Used in the plant for stem elongation, due to elongated cells and lots of division of cells.
It also causes buds to differentiate into reproductive organs. |
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How do anti-Gibberllins work?
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They cause stunted growth-- useful in Right-of-Way forestry.
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What is the function of cytokinins?
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Cytokinins stimulate cell division, delay senescence, and inhibits apical dominance.
Originate in plant roots. Cytokinins won't be produced in springtime until soil temperatures warm up. |
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How does ProShear work?
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If you spray cytokinins on a christmas tree, the side buds will elongate without you having to clip.
Disadv: too many buds develop and then the next year, the buds will only grow an inch. |
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What causes Witches Broom?
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A bacterial infection that produces crazy cytokinins that induce cell division at tree branch tips.
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What is the function of Ethylene gas?
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Induces abscision and senescence, induces/hastens fruit ripening.
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What is the function of Abscisic Acid and how does it work?
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It is a dormancy-inducing hormone.. there are very small amounts of this hormone in a tree.. normally found in buds and seeds.
AA is broken up over the winter due to cold/wet breaking. It forms again during the growing season, especially in Fall. It is also known to have an affect of stomatal closure. |
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Where will you find plants that have dormancy cycles?
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In areas where you have favorable and unfavorable growth environments.
Not generally at equator. |
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What are the 2 types of dormancy?
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1. Imposed/Enforced Dormancy- caused by unfavorable growth conditions. When unfavorable conditions are gone, plant will start growing again. (Not Trees)
2. Innate Dormancy- Dormant buds form when conditions are still favorable. If certain other things occur, that's when they will sprout. (This is Trees) |
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What are the 3 stages of Innate Dormancy?
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1. Predormancy- Dormancy is still reversible at this point because lateral buds are being held in check by auxin. As the growing season progresses, the chances for reversal get worse.
2. True Dormancy- No growth occurs, even under favorable conditions. They are waiting for a period of coldness (1.5-2 months) before they will come out of it. Growth regulators are breaking down and it takes 6 weeks of 2degreesC to go into postdormancy. 3. Postdormancy- They are ready to go, just waiting for favorable conditions (warmer weather). The buds are no longer innately dormant, they are imposed dormant because they are just waiting on the weather. |
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Attributes of Developing Dormancy
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1. Daylength: long days promote vegetative growth, short days induce dormancy
2. Temperature: cold can hasten dormancy 3. Mineral Nutrition/Fertilizer: flush nutrition out of soil, esp. Nitrogen, to induce dormancy 4. Water supply: a little bit of drought stress will induce dormancy |
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How to get plants to release from dormancy (after chilling)
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1. Warm soil temp
2. Lengthen Daylight 3. Fertilize 4. No water stress |
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Ecotype Effects
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Northern Races require a longer photoperiod to stay growing-- if moved south, they grow for a shorter time.
Southern Races require a shorter photoperiod-- if moved north, they grow for a longer period of time. |
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What is the Liquid-Mosaic Model?
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Water needs to stay in a liquid state inside the living tree cells and the cell membrane has to stay in a liquid state.
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Chilling Injury
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Occurs before freezing temperatures when the membrane becomes solid.
The membrane is made up of lipids.. Unsaturated lipids are liquid at room temp, Saturated lipids are solid at warmer temps. |
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What do membranes have to do to prepare for winter?
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Tree membranes have to switch from being unsaturated to being saturated.
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What are the 2 mechanisms of Cold-Hardiness?
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Supercooling, and Intracellular dehydration.
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Describe Supercooling.
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Tree will remove all nucleating centers so no ice crystals form. Ice crystals can form in intermembranes, but since the pores in cells are smaller than an ice crystal, the crystal won't come in and disrupt the cell.
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Describe Intracellular Dehydration.
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Cells will get rid of all their water. They are in a dormant state that allows tree to survive desiccation. Water just moves into the intercellular area. These types of trees can survive even colder temperatures (down to liquid nitrogen.)
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