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54 Cards in this Set
- Front
- Back
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What are 3 features of cells that are distinctive and typical of plants? |
1. @ cell level: cellulose walls, vacuoles, chloroplasts 2. @ whole-plant level: roots, leaves 3. transport systems: xylem, phloem |
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What are 5 characteristics that might define a good model plant? |
1. Small genome -- simple 2. Short life cycle -- fast 3. Easily accessible -- available 4. Genomes determined --understood 5. Understand functions -- manipulative |
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What are three major kinds of plant tissue? |
1. Dermal - epidermis: single layer of cells - cuticle: waxy layer to prevent water loss - guard cells: regulate gas exchange at stomata - root hairs: increase surface area and water uptake
- fxns: photosynthesis, storage, support - parenchyma: thin-walled cells; site of metabolism and photosynthesis; can be found in xylem - collenchyma: narrow, elongated cells w/ thick primary walls; supports plant and stretches as it grows; found in stem periphery, petioles - sclerenchyma: made up of sclereids and fibers --> usually dead w/ thick 2ndary walls --> sclereids vary in shape; found throughout the plant; mechanical support --> fibers are narrow, elongated; associated w/ vascular tissue cells
- fxn: mechanism for water and nutrient transportation - xylem: conducts/transports water and nutrients; *parenchyma and sclerenchyma cells present; conducting tissues = tracheids and vessels --> tracheids (gymnosperms) --> vessels (angiosperms) made of vessel elements - phloem: conducts/transports sugars and signal molecules; *parenchyma and xylem sclerenchyma fibers present; conducting tissues = sieve cells and sieve tubes --> sieve cells (gymnosperms) --> sieve tubes (angiosperms) made of sieve elements |
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What is the function of dermal tissue? |
1. Protect plant |
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What are the three major kinds of (ground) tissue? |
Parenchyma, Collenchyma, Sclerenchyma |
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What are the characteristics and functions of parenchyma? |
Characteristics: (1) thin-walled, (2) metabolically active cells, (3) functional in metabolism |
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What are the characteristics and functions of collenchyma?
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Characteristics: (1) narrow, (2) elongated cells with thick primary walls
Function: (1) structural support to growing body (can stretch as organs grow) (found in stem periphery, petioles, growing shoots and roots) |
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What are the characteristics and functions of sclerenchyma?
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Characteristics: (1) short sclereids, (2) thick fibers (both with thick secondary walls), (3) frequently dead at maturity |
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What are the differences between sclereids and fibers in sclerenchyma?
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Sclereids: spherical, branched, widely distributed throughout plant
Fibers: narrow, elongated, associated with vascular tissue |
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Describe diversity of plants and plant physiology. |
Taxonomic diversity: seed plants -> gymnosperms, angiosperms |
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Please give three reasons that plants need water, and indicate which of the three reasons accounts for the bulk of the water used.
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1. Growth - plants must stay hydrated within narrow limits or... growth will cease, tissues become stressed, plant wilts/dies
2. Turgor pressure - force on cell wall by water (and vacuoles) gives the plant rigidity --> helps keep it erect (*too* much turgor can burst the cell)
3. Transpiration (cost) - opening up stomata for CO2 gas exchange for photosynthesis exposes moist interior to drying air --> water lost as side effect: transpirational cost - allows plants to cool (side effect); evaporation of water during transpiration dissipates heat energy, keeping plants under sunlight a few degrees cooler than air |
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Property: Water is a supersolvent.
Why? Give an example. |
- due to small size of H2O and its polar nature - especially good as solvent for ionic substances, sugars, and proteins with polar groups - H-bonds form between H2O molecules and organic ions stabilize the ions and increase solubility |
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Property: Water has high specific heat (and high latent heat of vaporization.
Why? Give an example. |
- H-bonds give H2O high specific heat (energy required to raise the temperature of water by 1 degree Celsius) - high latent heat of vaporization (energy required to move molecules from liquid to gas phase) due to H-bonding - lot of energy required to break many H-bonds |
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Property: Water has a high tensile strength.
Why? Give an example. |
- cohesion gives water a high tensile strength (the pull a continuous column of water can endure before breaking) - H-bonding makes water molecules strongly attracted to each other (cohesion), and an air-water interface minimizes surface area, allowing water to be pulled like a rope - pull = negative pressure = tension - Pressure = Force/Area - negative pressure can develop in water if no air bubbles - if air bubbles contaminate water, bubbles expand under tension, breaking the water column (cavitation) - tensions are very important--transpiration pulls water from roots to the leaves |
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Property: Water has high surface tension (and capillarity).
Why? Give an example. |
- H2O molecules strongly attracted to each other by cohesion because of H-bonding - an air-water interface minimizes surface area - expanding surface area requires breaking H-bonds - surface tension: energy required to increase surface area; influences shape of air-water interface and creates a net force at interface if curved - surface tension dissolves bubbles because air-water interface exerts an internal pressure=2T/r (T=surface tension of liquid; r=radius of bubble) --> air in a bubble resists shrinkage but as air dissolves into water, bubble collapses due to surface tension - water also attracted to solid phase, with charged groups especially (i.e. cell walls, glass surfaces) = adhesion - cohesion + adhesion + surface tension = capillarity - water is driven to climb walls of a container by adhesion; high surface tension leads to minimizing of air-water interface; cohesion pulls rest of water upward - water rises until force is balance by weight of water column --> water rises higher/faster in smaller tubes - in cell walls, capillaries have tiny radius (~100nm) so pulls water in very strongly and cell wall surface remain wetted throughout plant - capillarity may contribute to water movement from soil to leaves in seedlings, but not in all trees/higher plants |
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Give the equation (and driving force) for diffusion. State where in the plant you would expect it to apply. |
Equation: flow = -D (delta C/delta x) Driving force: concentration gradient (delta c/delta x) = Fick's Law Transport coefficient: diffusion coefficient (D)
Where in plant: - important for transpiration from leaves to air - movement of solutes within cells - movement of signal molecules across plasmodesmata |
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Give the equation (and driving force) for bulk flow. State where in the plant you would expect it to apply. |
Equation: flow = Kh (delta psiP/delta x) = Darcy's Law Driving force: pressure gradient (delta psiP/delta x) Transport coefficient: hydraulic conductance Kh
Where in plant: - xylem conduits and tubes
Bulk flow important for movement of sap in xylem and phloem through roots, stems, and leaves. Important for movement of water in soil and through plant cell walls. |
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Give the equation (and driving force) for osmosis. State where in the plant you would expect it to apply. |
Equation: flow = Lp/delta psi Driving force: water potential gradient -- delta psi Transport coefficient: membrane conductivity Lp
Where in plant: - cell membranes (selectively permeable) -- water crosses membranes by diffusion through lipid bilayer and aquaporins - concentration and pressure gradient determines water potential gradient in osmosis - solute potential: more solutes --> lower solute potential and overall water potential (psiS = -RTc) gravity potential causes water to move downward (0.01 MPam^-1 x height) negligible at scale of cell; gravity potential is 0 or - - water flows from high water potential to low water potential until cells come to equilibrium with surroundings (water potential of cell and surroundings are same, no net water movement) |
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What are two concepts/approaches to measure plant water status? What is an advantage of each? |
1. Relative water content = [(fresh mass - dry mass) / (saturated mass - dry mass)] x 100% Con: don't know how much water will be sucked into a leaf and its ability to take on water |
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Why is it difficult for plants to withdraw water from dry soil? What is the type of water transport, driving force, and transport coefficient? How does the driving force depend on the soil moisture? How does the transport coefficient depend on the soil moisture? |
SOIL HYDRAULIC CONDUCTIVITY is LOWER -Depends on soil type, structure (clay vs sand), and moisture
Type of water transport: Bulk flow Driving force: pressure gradient (delta psi P / delta x) Transport coefficient: Kh hydraulic conductance
Driving force (a pressure gradient) depends on soil moisture because... - Drier soil holds less water, thus more negative water potential. Solute potential is almost always 0 if soil is not saline. Water potential depends on pressure potential.
Transport coefficient (Kh) depends on soil moisture because... - is hydraulic conductane and depends on soil moisture. Greater the negative soil water potential (i.e. drier the soil), lower the soil hydraulic conductivity. - as soil dries, hydraulic conductivity drops and depends on how much soil is present. |
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What is the role of the Casparian Strip in water uptake and ion uptake in the root? What is the name of the tissue involved? How doe water cross this tissue? Why do plants invest in such a tissue? |
Function: Structure with suberized, hydrophobic cell walls that prevents water from entering apoplast (cell wall continuum). Water cannot flow via cell wall across the endodermis. |
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Explain the structure and function of the xylem by including the following terms: tracheid, vessel, pits, Poiseuille's Law, hydraulic conductance, conduit radius, cohesion-tension theory, cavitation. |
xylem: water pulled through conduits (tracheids and vessels for water movement)
- tracheids: universal in vascular plants (gymnosperms) - vessels: found only in angiosperms - pits: connect a series of tracheids/vessels --> xylem tubes allow hydraulic conductance (Kh) since xylem = tube system --> flows 10 bil x faster than if water had to move cell-to-cell to tree tops --> Kh related to 4th power of conduit radius (Kh = pi*r^4/8n)
- Poiseuille's Law: = pi*r^4/8n --> vessels much more conductive than tracheids; allow more rapid flows of water to leaf
- cohesion-tension theory: water drawn up to tree tops by tension in xylem --> challenge to plant: cavitation by air-seeding: air drawn into xylem conduits through pits --> air bubbles enter xylem and expand under tension --> fill xylem conduit, render xylem useless |
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Define cohesion-tension theory. |
How water is drawn up to the top of trees by tensions in the xylem through negative pressure. If tension gets too strong, the pits will fail. |
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Define air seeding. |
When air bubbles enter the xylem, they expand in the water under tension and fill the xylem conduit, rendering it useless.
- air drawn into xylem conduit through pits from surrounding airspaces - during cooling/freezing, air comes out of solution |
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Define root pressure. |
Found in some but not all plants. Roots transport solutes into xylem, which draws in water and builds up pressure in the xylem. The pressurized water in the xylem dissolves air bubbles. This is used mainly for flushing out air. |
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Define aquaporin. |
Water enters cells through aquaporins--protein channels for water; can be open or gated in response to environmental factors. |
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For a tree in the garden, there are 5 times as many xylem conduits in a branch than in a petiole, and the conduits in the branch are twice as wide as those in the petiole. About how many times higher is the hydraulic conductance in the branch? (Assume everything but these parameters is the same in the branch and the petiole). |
Pouiselle's Law, Kh=(pi)r^4/8*n(viscosity)
8n cancels out. |
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Explain structure and function of stomata, including the terms: guard cells, plasmodesmata, turgor, cellulose microfibrils, stomatal resistance. |
Stomata: allows gas exchange with environment; causes a negative water potential by evaporation of water from cell to air; refills xylem conduits with water uptake through roots
- guard cells: regulate opening of stomata via swelling; pressure --> guard cells open - plasmodesmata: tublar extensions of plasma membrane 40-50 nm in diameter tha traverse cell wall and connect two cells - turgor: turgor pressure in cells = pressure of water in vacuole and cytoplasm against plant cell wall; uptake of water causes turgor pressure in cells - cellulose microfibrils: differential wall thickening and arrangement of cellulose microfibrils dictate which parts of guard cells will stay fixed - stomatal resistance: depends on total area of stomatal pore (resistance increases as stomata close) |
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How and why is transpiration per leaf area affected by high stomatal aperture? |
Stomata more open = less stomatal resistance = increased transpiration
Stomal resistance depends on total area of stomatal pore (resistance increases as stomata close). |
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How and why is transpiration per leaf area affected by high wind velocity? |
Thinner boundary layer = increased transpiration
- lower transpiration if slow wind speed - boundary layer resistance depends on leaf size and wind speed |
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How and why is transpiration per leaf area affected by high temperature? |
Increased vapor pressure difference (VPD) = increased transpiration
- saturation water concentration increases exponentially with temperature - higher temp means higher leaf to air concentration gradient |
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How and why is transpiration per leaf area affected by low relative humidity? |
Increased vapor pressure difference (VPD) = increased transpiration
- higher transpiration since air inside leaf is considered to be far from saturation (i.e. moisture going out of the leaf) - high relative humidity means lower transpiration since more humidity = more moisture and air inside leaf almost saturated (100% relative humidity) |
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How and why is transpiration per leaf area affected by large leaf size? |
Larger boundary layer = decreased transpiration
- higher transpiration in larger leaves - boundary layer resistance depends on leaf size and wind speed (e.g. smaller leaf and higher wind speed leads to thinner boundary layer with lower resistance; larger leaf has more stomata) |
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UCLA has recently replaced the plants in the UCLA Court of Sciences with natives, on the basis that these will require less water. What traits would you measure at leaf or whole plant level to test whether this is indeed the case?
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Larger leaf size: larger boundary layer = decreased transpiration = needs less water.
Low stomatal aperture: stomata less open = more stomatal resistance = less transpiration. |
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Name the 7 macronutrients and 9 micronutrients. |
Macronutrients: Mg Si N K Ca P S (N most abundant, Si least)
Micronutrients: B Cl Cu Fe Mn Mo Na Ni Zn (Cl most abundant, Mo least) |
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Plant A has yellowing old leaves, while Plant B has yellow new leaves. What mineral deficiencies might they be suffering? Why do these different symptoms manifest?
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(Yellowing of leaves = chlorosis)
Chlorosis appears in young leaves as a result of deficiency in immobile nutrients (e.g. S, Ca) since nutrients end up here and are fixed. Deficiency may also induce production of anthocyanins and a purple color in the leaves (e.g. N, P) |
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Give two reasons why plant roots need to keep growing.
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1. To continually absorb nutrients. - adjacent to the root are depletion zones, as nutrients mobile in the soil (e.g. N) have been removed
2. To continually absorb soil-immobile nutrients (P) and provide anchoring of plant body to ground to store food/nutrients.
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Explain the role of mycorrhizae in plant mineral nutrition. |
Symbiotic mutualism between roots and fungi. |
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What is the overall reaction of photosynthesis?
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6CO2 + 6H2O + light energy (or irradiance) → 6O2 + C6H12O6 |
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What are the reactants and products of the light reactions? Where do the light reactions occur? |
Light reactions occur in the internal membrances of the thylakoid in leaf mesophyll.
Reactants: water, sunlight, NADP, ADP
Reactants: CO2, ATP, NADPH Product: Glucose |
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Why do plants harvest sunlight in the same range of wavelengths as the animal eye uses for vision? Include important properties of light and of the pigment molecules in your answer.
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At higher wavelengths: Less energy is produced. At high enough wavelengths, there is not as much energy to fuel the photosynthetic reaction. These reactions are endothermic; too little energy and not enough to run/produce the main pigment. Not enough energy to transmite chemical reaction into or electron transfer.
At lower wavelengths: More energy is produced. Higher than UV range results in breaking of bonds (OH, CC bonds). Plants don't want to use too much energy.
Light properties: - wavelength is inversely proportional to energy produced -enough energy is required to transfer energy from electrons |
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What is a pigment molecule, and how does it function? Use the following terms in your answer: light harvesting, absorption spectrum, conjugated double bond. |
Pigment molecules are used for light harvesting and function when a photon causes an electron to move to a higher energy state and the molecule becomes excited. - rich in conjugated double bonds to stabilize excited state of molecule - as a chlorophyll molecule returns to a less excited state, it releases energy by: emitting heat, emitting fluorescence, energy transfer or photochemistry - an absorption spectrum of a substance is a plot of its absorption of light against wavelength of light, to quantify its ability to take up light across the spectrum |
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What is meant by the Z-scheme of photosynthesis? Where is it located? |
Z-scheme of photosynthesis is the framework for understanding the light reaction. - movement of an electron during photosynthesis that consists of photosystems I and II, each with its own own antenna pigments and photochemical reaction centers, linked by an electron transport chain |
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What is the light harvesting antenna? Where is it located? |
Light harvesting antenna delivers energy efficiently to the reaction centers with which they are associated. - generally 200-300 chlorophylls per reaction centers in higher plants - embedded in the thylakoid membrane |
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Sketch out the electron transport reactions, and describe how ATP is produced.
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Short: H20 enters PSII and REDUCES into O2.
Light excites chlorophyll which causes electron rearrangement in reaction center. The excited chlorophyll passes the electron to plastoquinone. PSII passes its electrons to plastoquinone (Q), generating plastohydroquinone (AH2) which passes electrons to cytochrome B6F complex. One electron moves towards plastocyanin while other goes through cyclic process which pumps more protons into lumen. Plastoquinone and plastocyanin carry electrons between PSI and PSII. PSI passes electrons to ferredoxin which reduces NADP+ to NADPH. Under certain conditions, cyclic electron flow occurs in which PSI passes electrons to cytochrome B6F complex which results in more protons pumped into lumen. ATP is produced through photophosphorylation. The accumulation of H+ in the lumen creates a chemical and electric gradient, known as the proton motive force. This driving force causes H+ to diffuse through a specialized enzyme complex in the membrane, which harnesses that force to generate ATP from ADP. |
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Sketch out three main components of the Calvin Cycle.
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(1) Carboxylation (ribulose-1,5-bisphosphate acceptor is carboxylated, producing 3-phosphoglycerate)
(2) Reduction of 3-PGA, using ATP and NADPH, producing glyceraldehyde 3-phosphates (3) Regeneration of RuBP, using ATP |
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Name five ways that the Calvin Cycle is regulated. |
(1) Control of gene expression and protein biosynthesis, controlling the concentration of individual enzymes. - both high stroma pH and high Mg2+ activate Rubisco |
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Name two ways that the carbon reactions are chemically coordinated with the light reactions, so that they can run at the same rates. |
(1) Rubisco is activated by light-- which causes high stromal pH and high Mg2+ (released from the lumen to the stroma to balance the influx of protons; both activate rubisco). - reactions generate NADPH and ATP, so carbon reactions can convert CO2 into sugars. |
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What is photorespiration? What are reactants and products? Name the toxic byproduct and the cost of its disposal. Why this have evolved? |
Photorespiration: C2 oxidative photosynthetic cycle; occurs because rubisco is also an oxygenase - carboxylation rxn leas to fixation of O2 to RuBP when O2 levels are higher and CO2 levels are not significant
reactants: O2 --> RuBP and 5-C sugar RuBP breaks down to products 3-PGA and phosphoglycolate - phosphoglycolate is toxic byproduct because it is a peroxide - must dispose of phosphoglycolate using series of reactions spread out across 3 organelles (i.e. chloroplast, peroxisome, mitochondria) - cost of disposal: reaction needs ATP and NADPH from light reactions; 3-PGA regenerated for later uses
evolution: arose because plants evolved in distant past when CO2 levels were much higher --> O2 would not have competed effecively for rubisco - all plants share very similar rubisco enzymes, so presumably its basic function was fixed early |
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Sketch out the major steps of starch synthesis. How does this differ from sucrose synthesis, in metabolites and reaction location?
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Sucrose is a disaccharide composed of fructose and glucose. - synthesized in cytoplasm from triose phosphate products of Calvin Cycle used to make sucrose - exported to phloem tissue for transport for plant growth - regenerated during the day from photosynthetic products directly, and at night from the breakdown of starch - produced from UDP-glucose and fructose-6-phosphate (generation of UDP-glucose requires UTP)
Starch is a polymer of glucose - formed from ADP-glucose transported into the chloroplast --> stored in the chloroplast in leaf mesophyll cells and in amyloplasts in other cells throughout the plant - generation of ADP-glucose requires ATP - ATP used for starch synthesis and UTP for sucrose synthesis keeps these rxns compartmentalized
- both processes activated/deactivated separately
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Please write a brief paragraph decribing the diversity of plants and plant physiology. In your answer, please refer to numbers of species, and specific examples of diversity in growth form, in physiology and in adaptation to different habitats. |
1. Taxonomic diversity - seed plants: gymnosperms (~700 species) and angiosperms (~250k species)
2. Life form diversity - immense size variation, from duckweed (very tiny) to redwood and giant sequoia; 12 orders of magnitude in mass - growth form: trees (woody, single stem), shrubs (woody, multiple stems, shorter), herbs (non-woody), climbers - variation in habit: clonal populations, epiphytes, carnivorous plants
3. Biochemical and structural diversity - diversity in biochemistry and metabolism (C3, C4, and CAM photosynthesis) - diversity in nutrient and pigment concentrations, in hormone sensitivity, flowering cues - diversity in all aspects of structure (variation in cell sizes in tissues, leaf sizes, colors)
4. Diversity in whole-plant adaptation to habitat - irradiance habitats (plants thriving from <1% to 100% full daylight - moisture supplies (plants exist on chronically dry soil, ever-wet soil, or submerged in water) - temperature range (plants exist where temperatures reach <-40 and >-40) |
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What are 4 properties of water most important to plants? |
1. Water is a supersolvent 2. Water has a high specific heat 3. Water has a high tensile strength 4. Water has a high surface tension |
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What are the different roles in the plant of starch and sucrose? What makes these two molecules suitable for their different functions? What makes them unsuitable for the opposite function? |
Sugars are used for storage and transport of energy; better than ATP, which is a free radical, not easily controlled, and short half-life. Sugar is in an inert form, compressed energy bonds by reduction.
starch = storage; sucrose = transport
During the day... - an accumulation of sucrose in the cell will drive the synthesis and storage of starch. Surcrose breakdown and glucose byproduct enters the chloroplast and converts into starch in chloroplasts. (sucrose + glucose --> chloroplast --> starch)
At night... - starch is broken down to sugars in the chloroplast, which are exported out for sucrose production - formation of starch is inhibited at night - many cells grow at night, utilizing sugars derived from sucrose in phloem |
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What are the importances of compartmentalization and feedback in metabolic design? Give 2 examples of each in photosynthesis reactions. |
Compartmetalization: separates reactions from each other spatially and their reactants, so can be activated separately; allows fine-tuned and robust control of metabolic pathways and processes
Examples: - sucrose and starch compartmentalization; sucrose in cytosol, starch in chloroplast - photosystem I and photosystem II activated by light separately
Feedback: Same area; connections between two systems to regulate flow |
