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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)
Describe the steps involved in water transport?
- -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
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
- -CO2 depletion
- -an internal "clock" in guard cells
- -hormone abscisic acid is produced in response to water deficiency and causes the closure of stomata
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
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
What are the 9 essential macronutrients required by plants?
- macronutrients-N, P, K, S, Ca, Mg
- micronutrients-Fe, Cl, Mn, Zn, Cu, Ni
What is a major determinant of plant distribution & growth?
- Soil Quality-major determinant of plant distribution & growth
- -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
What are three major soil horizons?
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
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
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
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
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
What is the goal of sustainable agriculture?
- Goal of Sustainable Agriculture-conservation-minded and environmentally safe
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
What is the major contributor to the dry biomass of a plant?
-elements from inorganic pools
What is the main photosynthetic pigment? What are the accessory pigments?*
- -light reactions takes place in the thylakoids
- -Calvin cycle takes place in the stroma
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.
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
- 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
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