Survey
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• The loss of water vapor form the leaves and stems of a plant • Water generally moves into plants through their roots and upwards through the vascular system and out of the stomata in the leaves • Transpiration is regulated by the stomata • Tiny pores for gas exchange • Occur mostly in the leaves but sometimes found in the stem • Made of 2 elongated guard cells • attached to normal epidermis cells on one side • Not attached to each other • Open and close based on turgor pressure • Open when water is absorbed by the guard cell from its neighboring epidermis cell • Water is then lost through the pore • Close when enough water is lost that the cell becomes flaccid • Tend to be open during the day and closed at night • Will close during the day if plant becomes short of water • Regulates transpiration and prevents excess water loss • Water transport occurs in the xylem • Begins as elongated cells connected end to end • During development the end walls are dissolved away so long hollow tubes develop • Living tissues of xylem lay down cellulose which is thickened by lignin • Water lost by transpiration raises the osmotic pressure in the cells causing water uptake from surrounding cells and the xylem • As water leaves the xylem more is pulled up through transpiration pull and the cohesive/adhesive properties • As water leaves the xylem more is pulled into the xylem at the root • Much of the water pulled into the plants is lost to evaporation • Light • Stomata tend to be open in light • Light can warm the leaf and raise its temperature • Temperature • Causes evaporation of water molecules from the surface cells of the plant • Evaporation rate doubles for every 10 degree increase in temperature • Wind • Sweeps away water vapor • Humid Air • High water vapor surrounding the leaf • Soil water • Amount of intake by the roots must match transpiration • Carbon Dioxide • High levels cause the stomata to close • Huge, ever growing root systems increase the surface area for absorption of water and essential nutrients • Surface area is also increased by the addition of root hairs • Water enters due to higher solute concentration than soil • Cortex cells have a structure that also facilitates the uptake of water • Minerals needed by the plants and found in soil • are: • • • • N as NO3- or NH4+ K as K+ P as PO43Ca as Ca2+ • Diffusion • Minerals are more concentrated in the soil than in the root • When dissolved in water the minerals will diffuse into the roots • Mass flow of water • Uptake of water which includes dissolved minerals • Fungal Hyphae • Plants work together with fungus to absorb minerals • Threads of the fungus grow through the soil and absorb the minerals • The threads also grow into the roots and transport the minerals into the roots • These minerals would not be absorbed without the fungus • Plants give the fungus sugars • Use of metabolic energy to obtain minerals • Can occur against the concentration gradient • Cytosol of the cell holds some reserves of ions • Allows the cells to pull in more of these ions when available • Cells tend to horde ions • Highly selective – plant will choose from different forms of the same ion • Ions cross into the cell through pump molecules • If roots are deprived of oxygen then active transport stops • The formation of the necessary metabolic energy is from respiration • Thick cuticle • Prevents water loss through the external wall of the epidermis • Hairs on the epidermis • Traps moist air over the leaf • Reduction in number of stomata • Reduces areas where loss can occur • Rolled or folded leaves • Reduces area for transpiration to occur • Lower epidermis is rolled inside the leaf protecting it • Superficial roots • Takes advantage of condensation on the soil overnight • Deep and extensive roots • Allows access to the deep water • Reduced leaf numbers • Less surface area for transpiration • Low growth • Limits plant exposure to wind • Store water to dilute salt concentrations • Salt glands • Expel excess salt • Example is the mangrove • Specialized Vacuoles • Store Na+ and Cl• Prevents NaCl toxicity • Protected stomata • Stomata are recessed into the cuticle increasing the humidity and therefore decreasing transpiration • Reduced surface area • Sieve tubes • narrow elongated cells connected end to end; no real organelles • Sieve plates • end walls which have pores for material to move through • Companion cells • services and maintains the sieve tubes; attached to the sieve tube by cytoplasm strands • The movement of manufactured food (sugars and amino acids) • Occurs in the phloem • Can move in any direction • Goes from the source to the sink • The source is where the organic material is produced • The sink is where the organic material is used • Takes sugars to new growth in young plants and to storage in older plants • Amino acids are produced in the roots and transported to where they are needed for protein synthesis (usually growing parts of the plant) • Chemicals sprayed on the plant can also be moved in this manner • Aphid Stylets • • • • A way of getting uncontaminated sap from the phloem Aphids insert their stylets into the sieve tubes as a feeding mechanism The pressure in the sieve tube pushes the sap into the stylet Scientists can then remove the stylets and analyze its contents • Radioactively labeled carbon dioxide • Allows scientists to see where the carbon dioxide is fixed into sugar • This sugar can then be used to track the flow from the source to the sink • Involves active transport of the sugars and passive transport of water • Sugar is loaded at the source through active transport which causes water to also enter through osmosis • Increased water in the sieve tube causes and increase in hydrostatic pressure which causes movement of the sap • Sugar is removed at the sink and transformed to starch (or used) through active transport • Xylem then recycles the excess • Which osmoter is the source? • Which osmoter is the sink? • Which part of the plant is typically represented by osmoter A? • Which part of the plant is typically represented by osmoter B?