Photoshynthesis chapter 9


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  • Are in process of discussing phsyn. Makes glucose from CO 2 and H 2 O Extremely important to life on Earth.
  • Photons = light “package” Not all plants photosynthetic - beechdrops bacteria - cyanobacteria (blue- green algae) protists - Euglena, seaweeds (algae)
  • Primary producers, consumers = ecological terms 3rd category? (decomposers - gain nutrients from non-living organic matter - squirrel heaps
  • Talked a little about chloroplasts when talked about plant cells = organelles Chloro = green not in all plant cells- usually mesophyll chlorophyll - why plants green chloro = green phyll = leaf meso = middle mersophyll = ?
  • Look at electromagnetic spectrum = all the types of solar radiation ignore chloroplast picture for now go over visible light (light you can see) = very small part
  • Recap electromagnetic spectrum
  • Visible light most important for phsyn. Human eye not same as other organisms (insects) intermediate wavelength violet higher E than red red = longer wave, slower E - becomes important way to remember = rainbow
  • Wavelengths used for energ Different pigments absorb light of different wavelengths
  • Light can do 3 things when it hits a pigment different pigments absorb different wavelenths
  • Look at electromagnetic spectrum = all the types of solar radiation ignore chloroplast picture for now go over visible light (light you can see) = very small part
  • Usually just talk about chlorophyll, but important to realize other pigments there too carotenoids - why carrots orange
  • Now that understand pigments, nee to know chloroplast structure double membrane - like nucleus each compartment has specific function
  • 1. Very narrow 2. Look like green (Irish) pita bread membrane of thylakoid
  • Stroma throughout chloroplast space
  • Shows location of most chloroplasts hard to see
  • Let’s look at the actual process of phsyn. Not just one rxn as looking at molecular formula may indicate actually occurs in 2 stages 1st = leght rxns. Breaking bonds releases E - talked about Where O 2 that produced given off
  • Called light rxns. Cuz require sunlight photosystems imbedded in thylakoid membrane have clusters of photosynthetic pigments
  • Photosysterms prevent loss of energy as heat Antenna molecules (pigments) Chloro. A, b, carotenoida each photosystem has hundreds of pigment molecules
  • Chlorophyll a acts as if it had absorbed photon boosted, just like in previous example
  • Redox rxns. Important throughtout photosynthesis and cellular respiration redox stands for ….. Reduction because charge reduced - molecule becomes more neg. Oxidation because charge increased - molecule becomes more positive
  • In reality, 2 different photosystems occur characteristic chlorophyll a and primary acceptor molecules
  • Each photosystem absorbs light of slightly different wavelengths chlorophyll a molecules identical association w/different proteins in thylakoid membrane affects e - distribution in chlorophyll molecule = slight difference in light absorption
  • Already discussed have to keep e - flowing to keep energy flowing cyclic = circular/components recycled - electrons return to ground state non-cyclic = electrons don’t return to ground state
  • Golf course
  • Photoshynthesis chapter 9

    1. 1. Photosynthesis6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2O
    2. 2. Synthesizes energy-rich organic molecules (glucose) from energy-poormolecules (CO2, H2O).Uses CO2 as carbon source & light energy as energy source.Directly or indirectly supplies energy to most living organisms.
    3. 3. The major “Play-as” Fig. 10.4
    4. 4. Photosynthesis occurs in chloroplasts in eukaryoticorganisms:• Light dependent reactions occur in the thylakoidmembranes of the grana and yield ATP and NADPH(obtained by reducing NADP with H2O). O2 is a wasteproduct2. The Calvin cycle occurs in the space between granacalled stroma
    5. 5. Fig. 10.6
    6. 6. l Photo = lightl synthesis = putting togetherl = production of sugar (glucose = C6H12O6) using E from solar radiation (photons), CO2 and H2Ol Photons = fixed quantity of light El Utilized by most plants, some bacteria, some protists
    7. 7. Nutritional categories1. Autotrophs – require no organic nutrients. All can“fix” or reduce CO2 into glucose via the Calvin Cycle: 6CO2 + 12 NADPH + 18 ATP C6H12O6 + 12 NADP + 18 ADP + 18 PThey can then synthesize all other organic constituentsfrom this glucose
    8. 8. Autotrophs• Photoautotrophs – use light energy to generate boththe ATP and NADPH for the Calvin cycle.(photosynthetic organisms)B) Chemoautotrophs – cannot use light. Use respirationsof inorganic substrates like reduced sulfur compounds,nitrogen compounds, and iron to generate the ATP andNADPH for the Calvin cycle (all chemosynthetic organismsare bacteria)
    9. 9. 2. Heterotrophs – require at least 1 organic nutrient.Heterotrophs are dependent upon autotrophs, usually thephotosynthetic organisms, for a source of fixed carbon(ie carbohydrates) and other nutrientsPhotoautotrophs are considered “producers” in anecosystem. Heterotrophs are considered as “consumers”All life is therefore either directly or indirectly dependentupon the energy of the sun
    10. 10. l In eukaryotes, takes place in chloroplastsl Plants - chloroplasts in leaves, other green partsl Contain chlorophylll = green pigmentl captures/absorbs light E
    11. 11. Electromagnetic Spectrum Nm = nanometer = 10-9 m 0.0000000001 m Fig. 10.7 Based on WavelengthShort wavelength = high E Long wavelength = low E
    12. 12. Electromagnetic Spectruml Range = wavelengths of less than 1 nm (gamma rays) to wavelengths of more than 1 km (radio waves)l gamma = high El radio = low E
    13. 13. Visible Lightl Drives photosynthesisl = light detectable by human eyel 380-750 nml Ranges from violet redl ROY G BIV backwardsl red, orange, yellow, green, blue, indigo, violet
    14. 14. l Blue and red most important in photosynthesisl Why?l Colors (wavelengths) absorbed by chlorophylll Why is chlorophyll green?
    15. 15. l Light can be:l reflected, transmitted, absorbedl reflected - “bounces” off of pigmentl = color that you seel transmitted - goes through pigmentl absorbed - captured by pigmentl don’t see
    16. 16. Fig. 10.7+8
    17. 17. l Different pigments absorb different wavelengths of lightl pigment = substance that absorb visible lightl Wavelengths absorbed, disappearl black = all wavelengths absorbedl white = all wavelengths reflected/transmitted
    18. 18. Photosynthetic Pigments in Plantsl Chlorophyll al Chlorophyll bl = yellow-greenl absorbs slightly different wavelengthl Carotenoidsl = yellow & orangel Phycocyaninsl = blue and purple
    19. 19. l Chlorophyll a = primary pigmentl Chlorophyll b, carotenoids and phycocyanins = accessory pigmentsl Expand range of wavelengths available for photosynthesis
    20. 20. Absorption and actionspectra for photosynthesis Fig. 10.10
    21. 21. Chloroplast Structurel Lens-shapedl surrounded by double membranel divided into 3 compartments by system of membranes
    22. 22. Chloroplast Structurel 1. Intermembrane spacel = space between the 2 outer membranesl 2. Thylakoid spacel thylakoids = flattened membranous sacs inside chloroplastl Stacks of thylakoids = granal chlorophyll embedded within thylakoid membrane
    23. 23. l membrane separates thylakoid spacel = area inside of thylakoidsl from stromal 3. Stromal = thick fluid outside/surrounding thylakoids
    24. 24. Fig. 10.11
    25. 25. l Photosynthesisl - light (kinetic) E → chemical (potential) El E stored in bonds of glucose moleculesl Breaking bonds releases E
    26. 26. Photosynthetic Processl 2 stagesl 1. Light Dependent Reactionsl - require sunlightl 2. Light-Independent Reactions (Calvin Cycle)l - don’t require sunlight
    27. 27. l 1. Light Reactionsl convert light energy to chemical energyl energy stored in bonds of ATP & NADPHl - adenosine triphosphatel - Nicotinamide adenine dinucleotide phosphate
    28. 28. Light energy harvesting occurs via photosytems inthylakoid membranes: ADP + P + NADP + H2O + light energy ATP + NADPH + O2 Involves 2 photosytems interconnected by an electron transport chain
    29. 29. Light Rxns.l Require sunlight = light dependent rxns.l Occur in thylakoid membranes of chloroplastsl Thylakoid membranes contain photosystemsl = light harvesting unitsl consist of reaction center, antenna molecules, and e- acceptors
    30. 30. Example of a photosystem Fig. 10.13a
    31. 31. Excitation of an isolated chlorophyl molecule Fig. 10.12
    32. 32. l Reaction Center = single, specialized chlorophyll a molecule + primary e- acceptorl Antenna molecules = all other photosynthetic pigment moleculesl (chlorophyll b, carotenoids, phycocyanins)l e- acceptor molecules = molecules that accept electrons from “excited” chlorophyll molecules
    33. 33. How photosystems workl 1. Antenna molecules absorb photonsl 2. Pass energy from molecule to molecule until rxn. center reachedl 3. Chlorophyll a molecule in rxn center donates excited e- to primary e- acceptor
    34. 34. Photosystemsl Chlorophyll a molecule at rxn. center loses e- to primary e- acceptorl = electron transferl e- excitedl boosted to higher energy state
    35. 35. l Transfer of e- from chlorophyll a to primary acceptor = redox rxn.l = reduction/oxidation rxn.l Reduction = gain of e- = more negative chgl Oxidation = loss of e- = more positive chgl primary acceptor gains e- (reduced)l chlorophyll a loses e- (oxidized)l = first step of light rxns.
    36. 36. l Thylakoid membrane contains 2 types of photosystemsl - photosystem Il - photosystem IIl each has characteristic rxn. centerl systems cooperate
    37. 37. l Photosystem Il rxn. center absorbs light having wavelength of 700 nml = P700l Photosystem IIl absorbs light having wavelength of 680 nml = P680
    38. 38. l 2 systems cooperate to generate ATP & NADPHl ** = PRIMARY FUNCTION OF LIGHT REACTIONS **
    39. 39. Non-cyclic electron flow generates ATP and NADPH Fig. 10.14
    40. 40. Non-cyclic e- flow“mechanicalanalogy” Fig. 10.15
    41. 41. Chemiosmosis of ATPFig. 10.18
    42. 42. Chemiosmosis in mitochondria and chloroplasts:10.17
    43. 43. Light Independent ReactionsCO2 fixation via the Calvin Cycle (recall from previousNotes) 6CO2 + 12 NADPH + 18 ATP C6H12O6 + 12 NADP + 18 ADP + 18 P See Fig. 10.17 for normal C3 pathway:
    44. 44. CalvinCycle Fig. 10.19
    45. 45. CalvinCycle6 CO2’s yield1 glucoseOccurs inStromaCatalyzed byRubisco(RuBP)
    46. 46. Photorespiration:- CO2 enter the plant leaf openings called stomata-these openings are surrounded by guard cells whichwhen flaccid close the opening-During dry conditions, stoma are thus closed and CO2becomes limiting-The Rubisco enzyme then reacts with O2 rather thanCO2 and photorespiration occurs instead of CO2fixation
    47. 47. Photorespiration: - Photorespiration wastes fixed carbon by converting ribulose biphosphate into only 1 glyceraldehyde phosphate plus 1 glycolic acid (CH2OHCOOH) -this glycolic acid is removed from the cycle and is Wasted -plants evolved photosynthetic pathways to prevent this wasteful process
    48. 48. C4 Plants and the C4 Photosynthetic Pathway: -Occur/originated in tropics, Mediterranean -Adapted to hot/arid environment -Adaptations save water, prevent photorespiration
    49. 49. l Initial enzyme = PEP (phosphoenolpryuvate), fixes C into 4 C molecule (oxaloacetate)l Rubisco not involved initiallyl - eliminates photorespirationl C stored in 4 C molecule in mesophyll cellsl Calvin cycle occurs in nearby cellsl = bundle sheath cells
    50. 50. l Mesophyll cells shuttle C to bundle sheath cellsl Allows photosynthesis to occur even if stomates closedl Examples: corn, sugarcane, Bermuda grass
    51. 51. C4 anatomy and pathway: Fig. 10.20
    52. 52. l C4 can handle heat, drought, high lightl C3 more efficient if water is available and under lowlight conditions
    53. 53. CAM Plantsl = Crassulacean Acid Metabolisml - Cacti, pineapples, succulentsl Open stomates at nightl - lets in CO2, minimizes water lossl CO2 incorporated into organic acids (stored)l Used in light rxns during day while stomates closed
    54. 54. Comparison ofC4 and CAM Fig. 10.21