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What is water potential? How do solute potential and pressure potential affect it?
- -water potential = all the forces that determine the direction of water flow
- -affected by pressure & solute concentration
- -water potential = (solute potential (psi_s) and pressure potential (psi_p)
- -water enters plant by osmosis until (psi_p =psi_s)
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Describe the steps involved in water transport?
- -osmosis
- -flow of water:
- - high water potential -> low water potential
- - soil water potential > root water potential, then water flow from soil -> root
- -flow of water usually powered by loss of water from leaves (transpiration)
- -transpiration pulls water up plant
- -diffusion of water vapor from humid air inside leaf to drier air outside lead
- -loss of water generates force that pulls water into leaf from vascular system, from roots, from soil
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How do stomata open and close?
- -stomata open during the day and close at night to minimize water loss
- -stomatal opening at dawn is triggered by
- -light
- -CO2 depletion
- -an internal "clock" in guard cells
- -hormone abscisic acid is produced in response to water deficiency and causes the closure of stomata
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Compare symplastic and apoplastic flow of water in roots. What is the function of the casparian strip?
- -apoplastic consists of the cell walls which lie outside the plasma membrane.
- -continuous meshwork through which water and solutes can flow without ever having to cross a membrane
- -symplastic passes through continuous cytoplasm of the living cells connected by plasmodesmata
- -movement of water and solutes into the symplasts is tightly regulated
- -role of caspian strip acts as a seal that prevents water and ions from moving through spaces between the endodermal cells; instead, water and ions enter the cytoplasm of the endodermal cells
- -think tight junctions in animal cells
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Describe the steps involved in sugar translocation in plants.
- -transport of organic nutrients in the plant through phloem
- -powered by osmotic pump (solute=sucrose)
- -pressure flow hypothesis
- -sucrose pumped from photosynthetically active cells into sieve tubes (phloem loading)
- -as sucrose accumulates in sieve tube, water pulled into sieve tube by osmosis
- --> increases turgor pressure inside sieve tube
- -->flow of solution to attached sieve tube in which pressure is less
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What are the 9 essential macronutrients required by plants?
- macronutrients-N, P, K, S, Ca, Mg
- micronutrients-Fe, Cl, Mn, Zn, Cu, Ni
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What is a major determinant of plant distribution & growth?
- Soil Quality-major determinant of plant distribution & growth
- -texture
- -soil's general structure
- -various sizes of particles derived from breakdown of rocks
- -composition: soil's organic (humus) & inorganic chemical components
- -topsoil: mixture of particles of rock & organic material
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What are three major soil horizons?
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Describe the role of cationic exchange in plant uptake of soil nutrients.
- cation exchange-cations displaced from soil particles by other cations
- -displaced cations enter soil solution and can be taken by plant roots
- -cations adhere to negatively charged soil particles
- -prevents leaching by percolating groundwater
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How does soil affect water availability?
- Organic Components
- -humus builds crumbly soil
- -helps retains water, but also maintains porous soil
- -increases soil's capacity to exchange cations & is a reservoir of mineral nutrients
- -topsoil contains many organism
- -bacteria, fungi, algae, protists, insects, earthworms, nematodes, & plant roots
- -help to decompose organic material & mix the soil
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Which mineral has the greatest effect on plant growth? How can plants increase the availability of this mineral?
- -Nitrogen is the mineral with the greatest effect on growth
- -required for proteins, nucleic acids, chlorophyll
- -nitrogen fixing bacteria convert atmospheric N2 to forms available
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Why are legumes efficient at obtaining nitrogen? How does Rhizobium benefit from its relationship with plants?
- Bacteria and Nitrogen Fixation-have a built in source of fixed nitrogen
- -often used as "green" fertilizer
- -legumes = symbiosis between plants and nitrogen fixing bacteria
- -bacteria = suger & anaerobic environment
- -plant = nitrogen
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How does a mycorrhizal symbiosis benefit fungus & plants?
- Mycorrhizal Symbiosis-Mycorrhizae = modified roots with mutualistic fungi
- -benefit to fungus = sugar
- -benefit to plant = water uptake and mineral absorption
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What is the goal of sustainable agriculture?
- Goal of Sustainable Agriculture-conservation-minded and environmentally safe
- -profitable
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What wave lengths of light do plants absorb? Why do leaves look green? What cells in leaves contain the most chloroplasts?*
- -plants absorb blue and red wave lengths of light
- -leaves look green because it reflecting the color green on the light spectrum
- -
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What is the major contributor to the dry biomass of a plant?
-elements from inorganic pools
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What is the main photosynthetic pigment? What are the accessory pigments?*
- -light reactions takes place in the thylakoids
- -photo
- -Calvin cycle takes place in the stroma
- -synthesis
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What is an absorption spectrum? Action spectrum?
- absorption spectrum
- -plot light absorbed by a purified pigment against wavelength,the result is an absorption spectrum for that pigment.
- action spectrum
- -an action spectrum is a plot of the biological activity of an organism against the wavelengths of light to which it is exposed.
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Photosynthesis consists of light and light-independent reactions—describe the major steps in each reaction and where they occur. Why do we consider photosynthesis a redox process?
- Photosynthesis-12H2O + 6CO2 + light -> C6H12O6 + 6O2 + 6H2O
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- Redox Reactions-oxidation = loss of electrons
- -removal of H+ (NADH -> NAD+)
- -C6H12O6 ->6CO2
- -reduction= addition of electrons (reduces positive charge)
- -addition of H+ (O2->H2O)
- -photosynthesis is a redox process
- -H2O is oxidized
- -CO2 is reduced
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How do C4 and CAM plants minimize photorespiration? How are CAM plants especially adapted to hot, dry environments?
-C4 and CAM minimize photorespiration by alternative photosynthesis pathways
- C4-special enzyme very efficient at binding CO2
- -bound CO2 exported to bundle-sheath cells, where used in the Calvin cycle
- -ie corn, sugar cane
- CAM-bind CO2 at night
- -convert CO2 to glucose at day
- -ie succulents, cacti
- CAM Plants-some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon
- -CAM plants open their stomata at night, incorporating CO2 into organic acids
- -stomata close during the day, and CO2 is released from organic acids and used in the Calvin Cycle
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