BIO 41,Ch7

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BIO 41,Ch7
2013-04-26 19:37:11
Photosynthesis Chapter Bio

Photoynthesis: Using Light to Make Food
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  1. Photosynthesis
    Process whereby plants, algae (which are protists), & certain bacteria transform light energy into chem energy, using carbon dioxide & water as starting materials
  2. In addition to CO2, Photosynthesis requires ______, which is absorbed by plant's roots & transported to leaves, where veins carry it to photosynthetic cells
  3. Chem energy produced via photosynthesis is stored in bonds of what?
    Sugar molecules
  4. Photosynthesis takes place w/in organeles called _____ using gases that are exchanged via pores called ______.
    chloroplasts; stomata
  5. Chloroplasts
    • Light-absorbing organelles that are concentrated in interior cells of leaves
    • All green parts of plant/algae contain these & convert sunlight into chem energy in Photosynthesis
    • In most plants, however, the leaves have most chloroplasts & are therefore major locations of photosynthesis (about 500,000 per square millimeter of leaf surface)
  6. Chlorophyll (Green color on leaves)
    • Selective absorption of other colors while reflecting/transmitting green light
    • Light-absorbing pigment in chloroplasts that plays central role in converting solar energy to chem energy
  7. Stomata
    • Tiny pores (singular, stoma, meaning "mouth")
    • Carbon dioxide (CO2) enters, & oxygen (O2) exits these
  8. Chloroplasts have a double-membrane envelope, just like a what?
  9. Membranes w/in chloroplast form framework where many of the reactions of......
    ....photosynthesis occur
  10. Stroma
    • A Thick fluid
    • Chloroplast's inner membrane encloses compartment filled w/ this fluid
  11. Thylakoids
    • Interconnected mambranous sacs suspended in stroma
    • --- Chlorophyll molecules that capture light energy are built into this
  12. Grana
    • Stacks where thylakoids are concentrated
    • (singular, granum)
  13. Structure of Chloroplast
    • Aids its function by providing large surface area for reactions of photosynthesis, w/ its stacks of disks
    • Chemical factories powered by the sun
  14. Chem equation: Relationship between Photosynthesis & Cellular respiration
    • ---Photosynthesis Reactants: CO2, H2O (are also waste products of cellular respiration)
    • ---Photosynthesis produces what Respiration uses: C6H12O6(Glucose) & O2(Oxygen)
    • Photosynthesis takes "exhaust" of cellular respiration & rearranges its atoms to produce food & oxygen
  15. In Photosynthesis, electrons are boosted _______ & added to CO2 to produce sugar, as a pose to cellular respiration causing their electrons to "fall"

    • -NEXT: Hydrogen moves along w/ electrons, so.....Redox process: Hydrogen transfer from H2O to CO2; this transfer requires chloroplast to split water molecules into hydrogen & oxygen.
    • -THEN: Hydrogen is transfered w/ electrons to CO2 to form sugar
    • -FINALLY: Xxygen escaped thru stomata into atmosphere as O2= Wast Product of Photosynthesis
  16. 2 Stages of Photosynthesis:
    • Calvin CYCLE
  17. Stage 1 Photosynthesis: LIGHT REACTIONS
    • Chlorophyll in thylakoid membranes absorbs solar energy, then is converted to chem energy ATP & NADPH
    • Water is split providing a source of electrons & giving off O2 gas as by-product
  18. NADPH
    • Electron carrier in Photosynthesis
    • Light drives electrons from chlorophyll to NADP+(oxidized form of carrier), forming NADPH (reduced form of carrier)
    • Provides high-energy electrons for reduction of CO2 to sugar in Calvin cycle
  19. Stage 2 Photosynthesis: Calvin CYCLE
    • Uses products of light reactions to power production of sugar from CO2
    • Enzymes from cycle are dissolved in stroma(thick fluid in chloroplast)
    • Indirectly DEPENDS on Light to produce sugar because it Requires: ATP (Sugar Synthesis Energy) & NADPH (High-Energy Electrons for Reduction of CO2 & Glucose) BOTH produced by LIGHT REACTIONS
  20. Sunlight
    • Type of energy called Radiation, or Electromagnetic Energy
    • Travels thru space as rhythmic waves; Analogous to ripples that are made by pebble dropped into pond
  21. Wavelength
    Distance between crests of 2 adjacent waves
  22. Electromagnetic Spectrum
    • Full range of radiation (From very short wavelengths of gamma rays to very long wavelengths of radio signals)
    • Visible light is small fraction of spectrum (Consists of wavelengths our eyes see as diff colors)

  23. When sunlight shines on pigmented material, certain wavelengths (colors) of the visible light are...
    • ...absorbed & disappear from light that's reflected by material
    • **Ex: Pair of Blue jeans, Pigments in fabric absorb other colors, leaving only light in blue part of spectrum to be reflected from fabric to our eyes
  24. Theodor Engelmann
    • German biologist OBSERVED that "Certain bacteria living in water tend to cluster in areas w/ higher oxygen concentration" in 1883
    • He knew light passed thru PRISM & separated into diff wavelengths (colors)
  25. What did Theodor Engelmann QUESTION?
    His info to determine which wavelengths of light work best for photosynthesis
  26. Theodor Engelmann's HYPOTHESIS
    Oxygen-seeking bacteria would congragate near regions of algae performing most photosynthesis (Producing most Oxygen)
  27. Theodor Engelmann's EXPERIMENT
    • Laid a string of freshwater algal cells w/in a drop of water on microscope slide.
    • Then added oxygen-sensitive bacteria to drop
    • Next, using prism, created spectrum of light & shined it on slide
    • RESULTS: Most bacteria congregated around algae exposed to red-orange & blue-violet light, w/ very few bacteria moving to green light
  28. Other than Theodor Engelmann's Main EXPERIMENT, what did his other experiments verify?
    That Chloroplasts absorb light mainly in blue-violet & red-orange part of spectrum & those wavelengths of light are ones mainly responsible for Photosynthesis
  29. Chloroplasts contain how many kinds of pigments?
  30. Chloroplast Pigment: Chlorophyll a
    • Absorbs mainly blue-violet & red light
    • Participate directly in light reactions
  31. Chloroplast Pigment: Chlorophyll b
    • Absorbs mainly blue & orange light
    • Doesn't participate directly in light reactions, but it broadens range of light that plant can use by conveying absore energy to chlorophyll a
    • It then puts energy to work in light reactions
  32. Chloroplast Pigment: Carotenoids
    • Family of yellow-orange which absorb mainly blue-green light
    • Some pass energy to chlorophyll a
    • **Protective Function of Other Carotenoids: They absorb & dissipate excessive light energy that would otherwise damage chlorophyll (Similar Carotenoids, which we get from carrots & certain other plants,┬ámay help protect our eyes from bright light)
  33. The falling autumn temp's cause an increase or decrease in levels of chlorophyll?
    • Decrease
    • **This allows color of longer-lasting carotenoids to show thru
  34. Chloroplast pigments are all built into thylakoid membranes, which are organized into light-harvesting complexes called?
  35. Photon
    • Fixed quantity of light energy; Discrete packets of energy
    • --The SHORTER the wavelength of light, GREATER the energy of Photon
    • **Ex: Photon of Violet light packs nearly 2x as much energy as Red light Photon
  36. When a pigment molecule absorbs a photon, one of pigment's electrons gains energy, & electron has become what?
    • "excited"
    • -- The electron has been raised from Ground State to an Excited State, which is HIGHLY UNSTABLE; so an Excited Elec. usually loses its excess energy & FALLS BACK to its Ground State almost Immediately
    • -- Most pigments merely Release HEAT ENERGY as their light-excited electrons FALL BACK (Black Auto Hood gets HOT on Sunny Day)
  37. The fluorescent light emitted by a glow stick is caused by a chemical reaction that excites electrons of a fluorescent dye. So....
    electrons quickly FALL BACK Down to Ground State, releasing energy in form of fluorescent light
  38. Photosystem
    • Light-gathering antenna that focuses light energy onto a reaction center
    • Has cluster of a few hundred pigment molecules, including chlorophylls a & b & some carotenoids == This cluster of pigment molecules functions as Light-gathering antenna
  39. Photosystem: Reaction Center & Primary Electron Acceptor
    When photon strikes 1 of the pigment molecules, energy jumps from molecule to molecule until it arrives at REACTION CENTER: Consists of a chlorophyll a molecule that sits next to another molecule called PRIMARY ELECTRON ACCEPTOR: Traps light-excited electron from chlorophyll a in reaction center.
  40. How Light Reactions Generate ATP & NADPH
    • 1.) Photons excite electrons in chlorophyll of water-splitting Photosystem, THEN Photons are trapped by PRIMARY ELECTRON ACCEPTOR. Water-splitting Photosystem replaces its light-excited electrons by extracting electrons from water, which RELEASES O2 during Photosynthesis
    • 2.) Energized electrons from water-splitting Photosystem pass down an ETC to NADPH-producing Photosystem, Chloroplast uses energy released by electron "fall" to make ATP
    • 3.) NADPH-producing Photosystem transfers its light-excited electrons to NADP+, reducing it to NADPH
    • ***2 Types of PHOTOSYSTEMS cooperate in Light Reactions
  41. C4 Plants
    • --They incorporate carbon from CO2 into 4-Carbon compound before proceeding to Calvin cycle
    • When it's hot/dry weather, it keeps its Stomata mostly closed, conserving water
    • BUT has enzyme that continues to incorporate carbon even when leaf's CO2 concentration is low (donates CO2 to Calvin cycle to nearby cell)
    • **Ex: sugarcane, corn
  42. CAM plants
    • CO2 is incorporated into 4-Carbon compound that banks it at Night & releases to Calvin cycle in Same Cell during day, Keeps Photosynthesis Going when Stomata's closed during daytime
    • Adapted to VERY DRY weather
    • Conserves water by opening stomata & admitting CO2 ONLY at night
    • **Ex: Pineapples, cacti, succulent (water-retaining) plants ALOE & JADE
  43. C3 Plants
    • The first organic compound produced in Calvin Cycle is 3-Carbon molecule
    • Widely distributed
    • Farmers face issue of growing it cause plants close their stomata on hot, dry days, REDUCING water loss but also prevents CO2 from entering leaves; Sugar Production CEASES
    • **Ex(Common Crops): Soybeans, Oats, Wheat, Rice
  44. Location of Light Reactions in Thylakoid Membrane
    • 2 Photosystems & ETC that connects them transfer electrons from H2O-->NADP+, reducing it to NADPH
    • NOTE: Mechanism of ATP Production during light reacitons VERY SIMILAR to Mechanism in Cell Respir.
    • In both cases, An ETC pumps Hydrogen Ions (H+) across a membrane-----Inner Mitochondrial Membrane in the case of Respiration & Thylakoid membrane in Photosynthesis
    • ALSO, ATP synthases use energy stored by H+ gradient to make ATP
    • MAIN DIFFERENCE: Food provides high-energy electrons in Cell Respir, whereas light-excited electrons flow down Transport Chain during Photosynthesis
  45. Hard-hat Analogy for Light Reacitons
    • Light Reactions absorb Solar Energy == Chem energy of ATP & NADPH
  46. Calvin Cycle: Makin Sugar from Carbon Dioxide
    • Functions like Sugar Factory w/in Stroma of Chloroplast
    • INPUTS: CO2 (Using its C) from air, as well as ATP (Using it Energy) & NADPH (Using its High-Energy Electrons)
    • Cycle constructs energy-rich sugar molecule====>Output
    • OUTPUT: *G3P (Glyceraldehyde 3-Phosphate)
    • Plant cell uses G3P as Raw material to make Glucose & other organic compounds (Cellulose, Starch) that it needs