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33 Cards in this Set
- Front
- Back
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Transpiration occurs as a two step process. what are the two steps and explain.
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1.) Evaporation of water from moist cell walls inside the leaf into substomatal space.
2.) Diffusion of water from substomatal space through stomata into the atmosphere. |
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What are two types of transpiration and how do each compare in total transpiration?
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Stomatal transpiration=90-95%
Cuticular transpiration=all remaining |
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What is the driving force for transpiration?
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The difference in water vapor pressure bewteen the saturated or nearly saturated internal air spaces of the leaf and the surrounding air.
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What are some factors that affect transpiration?
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Humidity, temperatuee, wind speed, and the water vapor concentration gradient (because transpiration is a diffusuion process)
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What is relative humidity and how does it affect transpiration
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Amount of water vapor in the air compared to what the air can hold at that temperature. The lower the Relative humidity, the steeper the water vapor pressure gradient, wich means greater transpiration.
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In a transpiring leaf, RH equals what?
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Almost 100%
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How does temperature affect transpiration?
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Affects the same way as humidity does. They actually work together. The higher the temp, the high the saturation vapor pressure, which means if water vapor content does not change, humidity goes for example.
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What affects the thickness of the boundry layer?
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Leaf size, Leaf shape, Leaf hairs, and wind speed. The higher the wind speeds, the the thinner the boundry layer.
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What is the function of the xylem?
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Transportation of water, dissolved minerals, and some small organic molecules from roots through the stem to the aerial part of the plant.
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What does the xylem consist of and what is the function of each?
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1.) Schlerenchyma cells - structural support
2.) Parenchyma cells - for storage and lateral translocation of solutes 3.) Tracheary elements - conducting water |
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What are the conducting cells of the xylem?
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Tracheids and vessel elements
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What facilitates the rapid and efficient transport of water throughout a plant and why?
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Vessel elements because they have open end walls and are arranged end to end to form larger units called vessels
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Of the two cells of the xylem, what type of plants can each eb found in?
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Tracheids can be found in all vascular plants while vessel elements may only be found in most angiosperms and a few gymnosperms.
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What leads to positive and negative hydrostatic pressures, respectively?
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Water compression and water tension
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What is cavitation?
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The collapse in the liquid phase tension due to gas bubbles
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Why can the xylem be considered a single continuous system of water conducting conduits?
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Because it has sufficient branching and interconnections
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What is the driving force required to move water through the xylem at a typical velocity
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10 orders of magnitude less than that required for transmembrance transport
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Why are vessels more important than tracheids for carrying water in angiosperms?
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Because the vessels are more numerous and have a larger diameter
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What is the most widely recognized theory in explaing long-range water transport through the xylen? Expain.
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The cohesion-tension theoru. Large negative hyrdostatic pressure leads to water tension, which elads to water being pulled through the xylem to the transpiring leaves. This is why xylem is lignified, to be able to withstand the tension water applies to it.
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What is the pressure difference required to move water from the roots to branches of the tallest trees? Is this possible if only capillarity or root pressure were the mechanism being used for transport?
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3 MPA, no because 3 MPa exceeds the value that could be acheieved by these.
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What cause positive pressure in the xylem and what causes it?
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Root pressure. Absorbtion of ions from the soil and their transport into the xylem making the root act as an osmotic cell. (HOW IS THE CAPARIAN STRIP INVOLVED?!)
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What favors root pressure?
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High soil water potentials and low transpiration rates.
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What drives xylem transport of water?
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Negative pressure tension in the leaves whihc is brought on by evaporation of water inside large air spaces in the spongy mesophyll. The air contacting with film of water on the cells causes a curved air interface during evaporation which induces the negative pressure tension. The greater the radius of the curvature, the greater the hydrostaitc pressure.
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What can cause bubble formation in the xylem, what can happen if this happens, and how is it prevented?
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Air seeding, which is when air is pulled in through microscopic pores, and freezing of xylem conduits lead to bubbles. When these bubbles expand under tension, it can lead to cavitation. The size of the tracheids and vessel elements restricts cavitation.
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What is field capacity and what is it a function of?
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The maximum moisture retaining ability of different soils, which is a function of soil particle size.
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What happens when soil water is at or below field capacity and why?
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Soil water is tough to get because the water will be under tension, because as it evaporates it tends to stick to soil particles creating large curved air water surface interfaces. This tension leads to a negative water potential.
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What amplifies the surface area for roots used for water absorbtion?
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Root hairs
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What is the permanent wilting percentage How does it vary between sand and clay?
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Percent of soil water content at which plants cannot balance water loss due to transpiration and hence lose turgor. 1-2% for sand and 20-30% for clay.
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What is available water?
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The difference in soil water content between field capacity and permanent wilting percentage.
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What are the four main functions of roots?
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1.)To anchor plants in their surroundings.
2.) To provide storage for carbohydrates and organic molecules. 3.)To synthesize molecules such as alkaloids and certain hormones. 4.)To absorb and transport water from the soil to the aerial plant parts |
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Due to their importance, how much will some plants invest in body weight to the roots?
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50% or more
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Where does the most rapid water absorbtion occur in roots?
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The region called the maturation zone, because this is this is athe are of the roots in which vascular tissues have begin to differentiate, which means it does not contain extensive amounts of suberin and lignin which hinder water flow, but it does contain root hairs, which increases the root surface area which increases water absorbtion.
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Diffrent regions of the root absorb water at different rates depending on transpiration rates. Explain.
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When transpiration is low, most water uptake occurs at the tip of the root, but when transpiration is high, the resulting increase in tension results in more uptake in the basal region of the root.
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