EEB 162 MT
What is an absorption spectrum and what is an action spectrum?
Absorption spectrum- plot of a substance's absorption of light against wavelength of light, to quantify its ability to take up light across the spectrum Action spectra- Plots of the response of a system (like products generated in a reaction) against light wavelength. Action spectra show what wavelengths of light can cause the reaction to proceed.
For a tree in the garden, there are five 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).
(5x2n)^4 = 10000n
Give two reasons why plant roots need to keep growing.
1) Roots are needed to reach mobile and immobile nutrient, and absorb water 2) Roots serve a structural support role by keeping the plant anchor in the ground
A cell has a solute potential of -0.5 MPa and a pressure potential of 0.2 MPa, and it is placed in a sugar solution of water potential - 0.8 MPa. Which direction does water flow, and for the cell at equilibrium what are the solute and pressure potentials and overall water potential?
Cell's water potential: 0.2 MPa + -0.5 MPa = -0.3MPa Since the water potential of the sugar solution is more negative, the water flows out Cell at equilibrium solute potential: -0.5 MPa pressure potential: -0.8 MPa -(-0.5 MPa) = -0.3 MPa overall water potential: -0.8 MPa
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 does water cross this tissue? Why do plants invest in such a tissue?
Casparian strip: a waxy strip consisting of waterproof material with suberized radial cell walls along the cell wall of the endodermal cells (dermal tissue) in the roots. It allows regulation of water movement into the root. Water enters cells mainly through aquaporins (protein channels), which can be open or gated in response to environmental factors. When the water reach the endodermis, the Casparian Strip blocks off the apoplast pathway, forcing water to enter the xylem through symplast pathway. This gives plant control over what goes into and out of the xylem.
What are the reactants and products of the light reactions?
REACTANTS: H20 (water), NADP+, ADP + Pi, and light pigments such as chlorophyll, carotenoids, and bilin pigments are given off inside PSII and PSI are components of the light reactions, and they are in the grans lamellae (PSII) and stroma lamella (PSI), respectively PRODUCTS: O2, NADPH, and ATP are given off the light reactions lead to a splitting of water, and the production of NADPH and ATP, to be provided to the carbon reactions. LOCATION: thylakoid membrane
What is light harvesting?
The process of using light as an energy source to power cell functions. Energy from antenna pigments is transferred to reaction center.
Why do plants harvest sunlight in the same range of wavelengths as the animal eye uses for vision? Please include the important properties of light and of the pigment molecules in your answer.
UV rays and higher are very damaging and can break bonds in protein, membrane and etc. Radio waves and IR are related to heat Electrons in the cells are vibrated and excited.
Under what conditions would C4 plants have an advantage over C3 plants?
Under hot, dry condition, high salinity with high O2 concentration, C4 plant would have advantage over C3 plant. At high temperature, Rubisco react quicker to O2 than to CO2, and also O2 become more soluble at higher temperature, thus there is an advantage of being C4 plant. C4 plant can open less stomata for the same amount of CO2 fixation under high irradiant. There for C4 plant have improved water use efficiency (CO2 fix per water loss).
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?
Water evaporation rate of leaves, stomatal pore size, and boundary layer resistance. Whole plant level = water loss in any pathway between two tissues or from soil up to leaves.
Please explain the role of mycorrhizae in plant mineral nutrition
a symbiotic relationship between roots and fungi; increase absorption area and particularly help with the acquisition of Phosphate
Plant A has yellowing old leaves, while Plant B has yellowing new leaves. What mineral deficiencies might they be suffering? Why do these different symptoms manifest?
Chlorosis: appear as yellowing of leaves -For mobile nutrients, such as N, P, K and Mg, chlorosis appears especially in old leaves, as nutrients are mobilized from the old leaves to transport to young leaves. -For immobile nutrients, such as S and Ca chlorosis appears in young leaves These plants are suffering from chlorosis. Plant A's old leave turn yellow because it is suffering from lack of mobile nutrient, such as N, P, K, and Mg. Plant B's new leaves turn yellow because it is suffering from lack of immobile nutrient such as S, Ca.
Cell A which has a solute potential of -0.6 MPa and a pressure potential of 0.1 MPa is placed next to Cell B, which has solute potential of -0.65 MPa and a pressure potential of 0.1 MPa. In which direction does water flow?
Flows from A → B
Sketch out the electron transport reactions, and describe how ATP is produced.
photon excite the chlorophyll of the reaction center, ejecting an electron. the electron is then pass through series of carrier, and eventually reduce NADP+. the process generate ATP 1) PSII oxidize water in the thylakoid lumen and release H+ into the lumen, pass electron to plasoquinone, forming plastohydroquinone. 2) cytochrome b6f oxidize plastohydroqinone, and deliver electron to plastocyanin 3) PSI oxidize plastocyanin, and pass electron to ferrdoxin, which reduce NADP+, generating NADPH 4) ATP is generated as proton diffuse from lumen to stroma through the ATP synthase. - ATP generated during light reaction is known as photophosphorylation. This occur by chemiosmosis mechanism. the accumulation of H+ in the lumen creates a chemical and electrical gradient, known as proton motive force. this driving force cause H+ to diffuse through a specialized enzyme complex in the membrane, which harness that force to generate ATP from ADP.
What is a pigment molecule, and how does it function? Please use the following terms in your answer: light harvesting, absorption spectrum, conjugated double bond
pigment molecules in plant absorb light within its absorption spectrum. Light harvesting occur when the light photon is used to excited the electron in the pigment to a higher energy state. When the electron return to a lower energy state, energy is release in one of 4 ways: emitting heat, emitting fluorescence, energy transfer, and photochemistry. Photosynthetic pigment such as chlorophyll are rich in conjugated double bonds, which stabilize the excited state
Under what conditions would C3 plants have an advantage over C4 plants? Please explain why.
under cool, moist condition with low O2 concentration C3 would have advantage over C4 plant. If O2 were low and photorespiration did not occur, C4 plant would require more quanta of light per CO2 than C3 plant for the same CO2 fixation.
What is the overall reaction of photosynthesis?
6CO2 (carbon dioxide) + 6H2O (water) + irradiance → C6H12O6 (glucose) + 6O2 (oxygen)
Define the following: a) Cohesion-tension theory, b) air-seeding, c) root pressure, d) Aquaporin
(a) Cohesion-tension theory: water drawn up to the top of trees by tensions in the xylem (b) Air seeding: cavitation by air seeding is a challenge to a plant. Air is drawn into xylem conduit through pits from surrounding air spaces or during cooling/freezing air comes out of solution. Air bubbles enter xylem and expand in water under tension, fill up xylem conduit, making it useless (c) Root pressure: found in some, but not all, plants (sometimes only seasonally); roots transport solutes into the xylem, which draws in water, which causes pressure build-up in the xylem. Pressurized water dissolves air bubbles, and when air is moist and transpiration low, water may eventually guttate from hydathodes in the leaves (d) Aquaporin: integral membrane protein channel that allow water to flow through the bilipid membrane, can be open or gated in response to enviornmental factors
For the following types of water transport, please give the equation, indicating the driving force. Also, please state where in the plant you would expect each type to apply:
(a) Diffusion Flow = -D x (∆c/∆x) Driving force: concentration gradient (∆c/∆x) Concentration gradient drops off rapidly with distance, diffusion is rapid over short distances Transport coefficient in diffusion: diffusion coefficient (D) → property of the diffusing substance and the medium Location: transpiration from leaves to air, movement of solutes w/in cells, movement of single molecules across plasmodesmata (b) Bulk flow Darcy's Law: Flow = Kh × (∆Ψp/∆x) Poiseuille's Law: Kh = πr4/8η → larger the radius, larger bulk flow thicker the liquid, smaller the bulk flow Driving force in Bulk Flow: pressure gradient (∆Ψp/∆x) Location: sap in xylem & phloem, through roots, stems and leaves, movement of water in soil and through plant cell walls (c) Osmosis Flow = Lp × ∆Ψ Ψ = Ψs + Ψp + Ψg Driving force: water potential gradient (∆Ψ) cell membranes selectively permeable, water crosses by diffusion through lipid bilayer and aquaporins
Please explain and give the basis for two of the following four properties of water, and give an example of why the properties are important for plant life:
(a) Water is a supersolvent. Water molecules are small and polar. As a result, water is a very good solvent for ionic substances/sugars and proteins with polar groups.Hydrogen bonds that form between water molecules and organic ions stabilize the ions and increase their solubility. Ions and nutrients are able to stay soluble. (b) Water has a high specific heat. Due to hydrogen bonding, water has a high specific heat and does not change temperature easily. The specific heat is the energy required to raise the temperature. With high specific heat, it requires a lot of energy to change the temperature within the plant, particularly useful for plants in the sunlight all day. (c) Water has a high tensile strength. Due to water's cohesion (which is another result of hydrogen bonding), water molecules have high tensile strength, which is the pull a continuous column of water can withstand before breaking. Water works like a rope that is being pulled on. Without air bubbles, this tensile strength allows transpiration to pull water from roots to the leaves. (d) Water has high surface tension. Surface tension is the energy required to increase the surface area. Surface tension influences the shape of the air-water interface, and creates a net force at the interface if it is curved. Due to water's cohesion, expanding surface area requires breaking hydrogen bonds. Surface tension breaks the air bubble and limits the cavitation in xylem from happening
How and why is transpiration per leaf area affected by (a) high stomatal aperture? (b) high wind velocity (c) high temperature? (d) low relative humidity? (e) large leaf size? For each, please state whether transpiration increases, and whether this is due to a change in vapor pressure difference (driving force) between leaf and air, or due to changes in boundary layer conductance or stomatal conductance.
(a) higher stomatal aperture increases - stomatal conductance (b) higher wind velocity increases - boundary layer conductance (c) higher temperature increases - vapor pressure difference (d) lower relative humidity increases - vapor pressure difference (e) larger leaf size decreases - boundary layer conductance A) When you have high stomatal aperture you are increasing transpiration because you are decreasing stomatal resistance, and increasing stomatal conductance. B) When you have high wind velocity you are increasing transpiration and this is because the boundary layer is thinner and therefore boundary layer resistance decreases and diffusion conductance increases. C) High leaf temperature increases transpiration and this therefore impacts the VPD. As air heats up it can hold more water so by increasing temperature in the leaf you have a higher vapor pressure in the leaf than outside, leading to an increase in transpiration. This therefore leads to a higher VPD. D) Low Relative Humidity would increase the transpiration rate and this is due to there being a low vapor pressure outside the leaf than inside the leaf therefore causing a higher VPD and a higher transpiration rate. E) A larger leaf size increases the leaf's boundary resistance therefore decreasing the boundary layer conductance and leading to a decrease in transpiration rate.
What three possible environmental conditions might promote the evolution of the C4 photosynthetic pathway? Why?
-C4 tends to originates in arid regions -Heat, drought, and/or salinity as important conditions promoting C4 evolution Heat: C4 plant have reduce photorespiration, thus it does spend less excess energy to break down photorespiration product compare to C3. Drought: in area with little water, C4 plant would survive better because it would lose less water to transpiration compare to C3 plant for the same amount of CO2 fixed Salinity: soil that higher in salt make it hard for plant to suck in water, thus C4 plant would have advantage compare to C3 because C4 is more efficient at using water. -Where temperatures are higher, C3 plants increase their photorespiration strongly, because Rubisco reacts quicker with O2, and also, O2 becomes more soluble at higher temperatures. So, there is greater advantage to being C4.
Name two ways that the carbon reactions are chemically coordinated with the light reactions, so that they can run at the same rates.
1) Light cause high stromal pH and high Mg+ concentration (Mg+ is release from lumen to balance the influx of proton), both of these condition activate Rubisco 2) four other calvin cycle enzyme are activated by light, via the ferredoxin-thioredoxin system. The ferredoxin electron acceptor from the light reaction modulate the activity of enzyme in the Calvin cycle.
Why does C4 photosynthesis have a cost? Please describe direct and indirect costs.
1) direct: Regeneration of PEP consume 2 ATP 2) indirect: If O2 were low and photorespiration did not occur, C4 plant would require more quanta of light per CO2 than C3 plant for the same CO2 fixation.
Sketch out three main components of the Calvin Cycle.
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
What are 3 features of cells that are distinctive and typical of plants?
1. Cell Wall Rigid, primarily cellulose, with proteins. Primary cell walls <1 micrometer (young, growing cells). Secondary cell walls have lignin deposits, can be several micrometers thicker, and are stronger. 2. Chloroplasts Typically 20-40 per cell; 5-8 micrometers long. Site of photosynthesis. 3. Vacuole Up to 80-90% of cell volume. Contains water, organic, inorganic ions, sugars, enzymes, metabolites. Important for osmotic regulation, generating turgor pressur (for growth and mechanical suppor), for storing compounds, and for degrading cells during senescence.
What are the three major kinds of plant tissues and their functions?
1. Dermal tissue: Regulation with interaction with surroundings; protection Epidermis, cuticle, guard cells, root hairs 2. Ground tissue: Metabolic processes; structural and mechanical support i. parenchyma (thin-walled, metabolic cells, metabolisms, photosynthesis) ii. collenchyma (narrow, elongated cells with thick primary walls → structural support) iii. sclerenchyma (cell types: sclereids and fibers → mechanical support) 3. Vascular tissue: Conduction of water and nutrients i. Xylem (functions in conductions of water and nutrients, conducting tissue composed of trachieds and vessels ii. Phloem (functions in conduction of sugars and signal molecules, tissue composed of sieve cells and sieve tubes)
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?
1. It is difficult for plant to withdraw water from dry soil because as soil gets drier, the water potential of soil is lower and soil hydraulic conductivity decrease. Water moves from high potential to low potential. Potential in drier soil is relatively low, making it hard for plants to withdraw water from soil. As soil dries, it loses conductivity soil water potential = Ψs + Ψp 2. Water transport: bulk flow Driving force: pressure gradient Transport coefficient: soil hydraulic conductivity 3. As soil gets drier air water interfaces become stretched between soil particles, generating a negative pressure because of surface tension, so Ψp becomes negative Ψp = -2T/r 4. Soil hydraulic conductivity depends on soil type and structure, and on how wet the soil is. As soil dries, soil hydraulic conductivity declines, as channels in the soil empty of water.
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% Advantage: simplest way to measure water plant water status Weakness: not very sensitive for measuring drought responses and tells us nothing about the forces for water movement 2. Water potential Advantage: can tell if a plant is sensitive to drought measurement and can tells us about the forces of water movement
Please give three reasons that plants need water, and indicate which of the three reasons accounts for the bulk of the water used.
1. Transpirational cost of photosynthesis → most of the water is used in this process a. Opening up stomata to access CO2 from the atmosphere loses water → water allows for the plant to remain within its narrow limits and continue performing photosynthesis 2. Transpiration as a means of cooling the plant: evaporation of water during transpiration dissipates heat energy, keeping plants under bright sunlight up to a few degrees cooler than air, passive cooling 3. Water in the plant body: hydration has to be maintained within narrow limit or growth will cease and tissue becomes stressed → plant wilts Lack of water will close the stomata, thus stopping the photosynthesis and potentially overheating the plant (proteins can degrade outside of their temperature range)
Name five ways that the Calvin Cycle is regulated.
1. control of gene expression and protein biosynthesis, controlling the concentration of individual enzymes 2. rubisco is activated by a specific enzyme, rubisco activase, which itself requires ATP for activation 3. rubisco is activated by light - which causes high stromal pH and high Mg2+ (Mg2+ is released from the lumen to the stroma to balance the influx of protonx); both activate Rubisco 4. Rubisco is deactivated by high sugar concentration 5. 4 other Calvin cycle enzymes are activated by light, via the ferredoxin-thioredoxin system. The ferredoxin electron acceptors from the light reactions modulates the activity of enzymes in the Calvin cycle
What are 5 characters that might define a good model plant?
1. short lifespan/life cycle (corn) 2. small, known genome --> easy to sequence and modify or manipulate (arabidopsis) 3. easily grown, quick reproduction 4. readily accessible, common 5. observable, measurable traits (brassica)
Please explain C4 photosynthesis, using the following terms: HCO3-, PEP carboxylase, mesophyll, Kranz Anatomy, plasmodesmata, malate, separation of pathways in space, water use efficiency
C4 photosynthesis is found in many monocots (grasses and sedges), as well as in many eudicot shrub (spinach and daisy family). C4 reduce photorespiration by concentrating CO2 near rubisco. A first reaction occur in the mesophyll cells, CO2 is transformed to HCO3- , which is fixed to 3-carbon Phosphoenol-pyruvate (PEP), by the enzyme PEP carboxylase ; this reaction produce a 4-carbon compound (often malate). Malate diffuse passively via many plasmodesmata to the bundle sheet cell. Bundle sheet cell contain many chloroplast which run Calvin cycle. Malate is decarboxylate down to 3-carbon pyruvate (which diffuse back to mesophyll cell), and CO2 (which enter C3 calvin cycle in the bundle sheet). C4 plant often have Krantz anatomy: enlarge bundle sheet, lots of chloroplast. No mesophyll is 2-3 cell away from the bundle sheath, many plasmodesmata connecting mesophylls cell and bundle sheet. At high temperature, Rubisco react quicker to O2 than to CO2, and also O2 become more soluble at higher temperature, thus there is an advantage of being C4 plant. C4 plant can open less stomata for the same amount of CO2 fixation under high irradiant. There for C4 plant have improved water use efficiency (CO2 fix per water loss).
Please explain CAM photosynthesis, using the following terms: stomata, Rubisco, malate, PEP carboxylase, water-use efficiency
CAM stand for Crassulacean acid metabolism. CAM is like C4 in that PEP carboxylase fixed HCO3-. But CAM allow for increase CO2 concentration by fixing HCO3- with PEP carboxylase at night (when the stomata open in CAM plant). Malate is stored in the vacuole. PEP is generated by breakdown of starch from the chloroplast. During the day, when the stomata are close, malate is release from vacuole, and break down to pyruvate and CO2. The release CO2 interact with Rubisco in the C3 calvin cycle. CAM lead to a huge water use efficiency (up to ten time higher than C3 plant), because the stomata only open at night. CAM plant also often have very water resistance cuticle. Some plants are "facultative" CAM, in which they carry on C3 photosynthesis under unstress condition, and switch to CAM in respond to water, heat or salt stress.
Please name the 7 macronutrients, and 9 micronutrients.
Macronutrients: N, K, Ca, Mg, P, S, Si Micronutrients: Cl, Fe, B, Mn, Na, Zn, Cu, Ni, Mo
What is photorespiration? What are the reactants and products? Please name the toxic byproduct and the cost of its disposal. Why might this have evolved?
Photorespiration, or the C2 oxidative photosynthetic cycle, occurs because rubisco is also an oxygenase; this reaction competes with carboxylation. This reaction read to fixation of O2 to RuBP, and the 50carbon sugar break down to 3-PGA and phosphoglycolate, which must be disposed of using a series of reaction spread across three organelle (chloroplast, peroxisome, mitochondrion). toxic byproduct: peroxide; reaction needs to use ATP and NADPH (cost of disposal) Photorespiration is a purely negative phenomenon that arose because plant evolved in the distant past, when CO2 level were much higher, so O2 would not have compete effectively for rubisco. Photorespiration may carry a benefit, possibly helping to use up excess energy, when the light reactions are over-stimulated by excess light. This reaction uses up ATP and NADPH, so could protect the light reactions.
What is a pigment molecule?
Pigment molecules help plants absorb light. They are rich in conjugated double bonds, which stabilize the excited state.
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?
Starch and sucrose are used in two distinctive process: storage and transport of energy. Starch is a polymer of glucose thus it is efficient in energy storage. Sucrose is a disaccharide composed of glucose and fructose. Sucrose small size allow it to be an efficient energy transport in plant.
Please explain the structure and function of the stomata, including the following terms: guard cells, plasmodesmata, turgor, cellulose microfibrils, stomatal resistance.
Stomata are required for control of water lost relative to CO2 gain. Plants can open pores to fix carbon when water is abundant, but close pores to save water when the water supply is low or leaf demand for CO2 is low. Stomata are controlled via guard cell swelling. Guard cells are dumbbell shaped cells in grasses and kidney shape in non-grasses. Differential wall thickening and arrangement of cellulose microfibrils dictates which parts of the guard cells stay fixed. The rest of the cell swells, causing pore opening. When guard cells swell due to turgor pressure, the stoma open. Differential wall thickening and arrangement of cellulose microfibrils dictate which part of the guard cell will stay fixed when guard cells are pressurized. Guard cells are pressurized by increasing Ψs in the cell via ion uptake or creating new organic ions in the cell. Guard cell are kept isolated from surrounding cell (no plasmodesmata) so their aperture is not directly dictated by water status of surrounding cells. However guard cell turgor is sensitive to light temperature, leaf water status, and CO2 concentration. Stomata resistance depends on total area of stomatal pore (resistance increases as stomata close). Stomata are pores that open when water supply is high to fix carbon and close when water supply is low to save water. Guard cells are dumbbell shaped cells in grasses, kidney-shaped in non-grasses. Due to differential wall thickening and the arrangement of cellulose microfibrils, part of the guard cells will stay fixed while the other parts will swell when the guard cells are pressurized, which leads to pore opening. Increasing water potential causes the cells to swell. Guard cells are kept isolated from surrounding cells which means they don't have plasmodesmata, so their aperture is not directly determined by the water status of surrounding cells. Guard cell turgor is sensitive to light, temperature, leaf water status, and CO2 concentration. Stomatal resistance increases as stomata close. Stomata are controlled by guard cell swelling (change in turgidity). Differential wall thickening and arrangement of cellulose microfibrils dictates which parts of the guard cells will stay fixed. The rest of the cell swells (change in turgidity), causing pore to save water when the water supply is low, or when the leaf demand for CO2 is low. When stomata are closed, stomatal resistance is greater. Guard cells are kept isolated from surrounding cells (no plasmodesmata), so their aperture is not directly dictated by water status of surrounding cells
Please sketch out the major steps of starch synthesis. How does this differ from sucrose synthesis, in metabolites and reaction location?
Sucrose is generated during the day through photosynthesis and at night through the breakdown of starch. UTP is needed for the synthesis of sucrose to drive the production of UDP-glucose, whereas ATP is needed for the synthesis of starch, allowing separate activation/deactivation. Both reactions occur during the day, but starch synthesis stops at night. Sucrose is synthesized in the cytoplasm and exported to the phloem for transport, whereas starch is synthesized in the chloroplast, then stored in the chloroplast. In starch synthesis, monomers of glucose are added onto the end of a chain by starch synthase, and the energy that drives this comes from the breaking of a (high energy) pyrophosphate bond. Sucrose synthesis on the other hand involves lots more metabolites and steps.
What is the light-harvesting antenna? Where is it located?
The antenna system delivers energy efficiently to the reaction centers with which they are associated. Diverse antenna pigments are involved, and energy is transferred from the antenna to the reaction center by florescent resonance energy transfers (nonradiative process, very efficient energy transfer process). Light harvesting antenna are made up of photosynthetic pigments associated in a noncovalent but highly specific way with proteins, forming pigment-protein complexes. Antenna function to funnel light energy toward the reaction center. Antenna of photosystem II is located primary in the grana lamellae, whereas antenna of photosystem I is located in the stroma lamellae. Sequence of pigments within the antenna shifts toward longer, lower energy red wavelengths (heat dissipated in the process). The most abundant proteins are light-harvesting complex II proteins - these bind 14 chlorophyll molecules.
Please write a brief paragraph describing 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.
There are about 700 species of gymnosperm, and 250,000 species of angiosperm. Plant can be as small as a duck weed which is less than 1mm in diameter, or as big as a giant sequoia which is about 110m tall. Plant varies in growth form such as tree, shrubs, herb and climbers. Plant also varies in living habit such as clonal population, epiphytes, or carnivorous. Plant exhibit huge range of biochemistry and metabolism such as: C3, C4, and CAM photosynthesis. Finally plants vary in habitat adaptation; plants can be found thriving from less than 1% sunlight to 100% sunlight. Some plants live on chronically dry soil whereas other live on wet soil or even submerges in water. Plant can live in temperature below 40C and above 40C
Please explain the structure and function of the xylem, including the following terms: tracheid, vessel, pits, Poiseuille's Law, hydraulic conductance, conduit radius, cohesion-tension theory, cavitation
Xylem conduit: tracheids (universal in vascular plants) and vessels (found only in angiosperms) dead, hollowed out cell: tubes with lignified cell walls; pits connect series of xylem conduits Xylem (vascular tissue): functions in conduction of water and nutrients; conducting tissue composed of tracheids and vessels Tracheids: universal in vascular plants Vessels: only in angiosperms, gymnosperm Gnetum, ferns; dead, hollowed out cells-tubes with lignified cell walls that make up a series connected by pits Pits: connect series of xylem conduits; may be simple or, in conifers, with a margos/torus Poiseulle's law: hydraulic conductance is depended on the conduit radius, thus the vessel's bigger radius allow for faster water movement compared to tracheid's smaller radius → vessels much more conductive than tracheids, allow more rapid flow of water to leaf Xylem "tubes" allow for a high hydaulic conductance (Kh) Since xylem acts a tube system, flows are 10 billion times faster than if water had to move cell-to-cell at the top of trees Cohesion-tension theory: water drawn up to the top of trees by tensions in the xylem Xylem function to transport water in plant. Xylem is a pipe system in plant made up of xylem conduit. These are dead hollowed-out cells, and they are connecting in series by pits. There are two type of xylem conduits: tracheids and vessels. Tracheids are universal in vascular plants, but vessels are only found in angiosperms. Water moves in xylem conduits by bulk flow. Cohesion-tension theory proposes that water is drawn to the top of the plant by tension in the xylem. According to Poiseuille's law, hydraulic conductance is dependent on the conduit radius, thus the vessel's bigger radius allow for faster water movement compare to tracheid's smaller radius. Cavitation occur when air bubble appear in the water column, beak the column, and expand to fill up the whole xylem conduit. This is due to water being drawn into xylem conduit through pits from the surrounding air space or during cooling/freezing. When air bubbles enter the xylem, they expand in the water under tension and fill the xylem conduit, renderig it useless.
What is meant by the Z-scheme of photosynthesis?
Z-scheme is the framework for understanding the light-reaction. z-scheme of photosynthesis mean that photosynthesis in plant constituted of 2 system that run in series: photosystem II and photosystem I.PSI preferentially absorb far-red light, PSII preferentially absorb red light. It is constituted of the 2 photosystems, each with its own antenna pigments and photochemical reaction center, linked by an electron transport chain.
What are the importances of compartmentalization and feedback in metabolic design? Please give two examples of each in photosynthesis reactions.
compartmentalization separate reaction from each other, spatially and in term of their reactant, so they can be activated separately. This allow for fine-tune and robust control. For example 1. Starch and sucrose are two distinct processes: using ATP as activator for starch synthesis, and UTP as activator of sucrose synthesis. 2. PSII and PSI is also an example of compartmentalization. Feedback inhibition: allows plant to modulate key steps of photosynthesis based on it's needs (respond to buildups or lack of a metabolite), so that all parts of the process can run in sync. Examples: 1. high sugar concentration inhibits rubisco, the key regulatory step of the Calvin Cycle (whose goal is to make sugar)
