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Chapter 10

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Chapter 10

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  1. Chapter 10 Chapter 10 Photosynthesis The conversion of radiant energy into chemical energy & Converting inorganic matter into organic matter

  2. Introductory Questions #11 • Name the three phases of the Calvin Cycle. Which phases require ATP and how much ATP would be needed for producing on glucose molecule? 2) What are the substrates that attach to the active sites of Rubisco? • How does a C3 plant differ from a C4 plant? Give 3 examples of a C3 & C4 plant. • What happens as a result of stomata closing? • Which type of plant undergoes photorespiration? Does photorespiration occur at night or during the day? How is photorespiration different from cellular respiration seen in the mitochondria? • How are C4 and CAM plants similar and how are they different? Give an example of both.

  3. Photosynthesis in Nature Autotrophs are biotic Producers; Ex. Photoautotrophs and chemoautotrophs; obtains organic food without eating other organisms Heterotrophs: are biotic Consumers; obtains organic food by eating other organisms or their by-products (includes decomposers)

  4. Visible Light • Wavelength range of: 380 nm – 760 nm • Colors include: R O Y G B I V Red: Lowest energy, Longest wavelength Violet: Highest energy, smallest wavelength

  5. Leaves: The Solar Collectors for Plants • Considered to be an organ of the plant • Site for Photosynthesis (lots of chloroplasts) • Cutin-thin wax layer helps to reduce or control water loss • Other features worth noting: -Upper & Lower epidermis -Stomata & Guard cells -Xylem & Phloem (vascular bundle sheaths) -Palisade & spongy Mesophyll -Trichomes • High surface area: Can cause water to be lost • See a definite trade off

  6. Chapter 10 Chapter 10 Photosynthesis The conversion of radiant energy into chemical energy & Converting inorganic matter into organic matter

  7. Overview of Chapter 10 • Autotrophs vs. Hetertrophs • Properties and Characteristics of Light • Chloroplast Structure & Function Key Pigments: Chlorophyll a & b, & Carotenoids • Light Reactions (Light Dependent)-Photosystems • Cyclic vs. Non-cyclic flow of Electrons ------------------------------------------------------------------------------- • Dark Reactions (Light independent)-Calvin Cycle • Photorespiration: ↓ Photosynthetic efficiency • C3, C4, and CAM Metabolic Pathways of Plants

  8. Properties of Light • Electromagnetic Radiation • Possesses properties of a particle and a wave • Generated when electrons move from a high energy state to a lower energy state. • Small portion of the EM spectrum (pg .157) • Composed of small “packets” or quantized amount of energy called PHOTONS • Described by Max Plank and DeBroglie

  9. Properties of Light (Pg. 186)

  10. Photons and Electrons • Photons interact with electrons and move electrons to higher energy levels from the “ground state” • When electrons “fall” to the lower ground state, and light is emitted as it falls. This light is called “Fluorescence”.

  11. The Chloroplast and Light (pg. 186) • The (3) Fates of Light as it interacts with a chloroplast.

  12. Structure of the Chloroplast • Double membrane • Has its own DNA • Internal membrane system called Thylakoids • Contains protein pigmets: ex chlorophyll a

  13. Internal Structure of a Leaf

  14. Introductory Questions #9 • Name three factors that can affect transpiration in plants. • How do plants absorb light energy? Name some features that allow plants to absorb light. What are some differences between chlorophyll a and chlorophyll b? • What did Engelmann’s experiment measure? What organisms did he use? • Which reactant does the oxygen produced from photosynthesis directly come from? • Where specifically do the light and dark reaction take place within a plant cell? • Name the three parts that make up a photosystem. • How does NADPH differ from NADH?

  15. The Leaf: The Site for Photosynthesis

  16. The Chlorophyll Molecule (Pg. 188) • Porphyrin ring (absorbs light) • Central Magnesium Atom • Hydrocarbon tail • Alternating double & single bonds • Similar to hemoglobin • History of Discovering Chlorophyll: http://www.chm.bris.ac.uk/motm/chlorophyll/chlorophyll_h.htm

  17. Typical Pigments Found in the Thylakoid Membrane • Chlorophyll a - important in light reactions • Chlorophyll b - accessory pigment - has a yellow/green reflection • Carotenoids – are yellow & orange • Anthocyanins– are red pigments • Fucoxanthin – is a brown pigment • Xanthophylls – are typically yellow

  18. Determining Absorbance of a Pigment (pg. 187)

  19. Lab #14: Plant Pigments & Photosythesis • Computer guided Lab using our typical Ph_school lab bench site • Two Parts: • Separation of pigments (Hon. Bio/Reg Bio.) • Oxidation/Reduction with DPIP • Key point about the lab: • The pigments separated by chromatography were: (top to bottom) • Carotene (orange)---Xanthophyll (yellow)----Chlorophyll a ----Chlorophyll b • DPIP has blue color acting as an electron acceptor: changes to colorless when it is reduced (gains the electron) • Oxidized DPIP will turn back to a blue color • As the samples become reduced (DPIP becomes colorless) the transmittance will be high and as it becomes oxidized (DPIP changes to blue) the transmittance will be low because of the amount of absorbance.

  20. Absorption & Action Spectra (pg. 187)

  21. Engelmann’s Experiment (pg. 187) • Obtained the first action spectrum in 1883 • Used Spirogyra w/spiral shaped chloroplasts • Exposed this alga to a color spectrum using a prism • Measured photosynthesis by using certain motile bacteria that would be attracted to the oxygen released by photosynthesis. • Control: Ensure that the bacteria were not attracted to the colors, he conducted the experiment without spirogyra. No preference was shown by the bacteria.

  22. Discovering the Process of Photosynthesis • For centuries gardeners have asked the perplexing question: “Where does the mass of a tree that weighs several tons come from when it starts as a seedling weighing only a few grams?:” • Does it come from: -Soil -air -water

  23. Experiments conducted probing this Question • Jan Van Helmont - accounted for the water (hydrate) aspect of photosynthesis • Joseph Priestly – accounted for the release of oxygen by photosynthesis using a a burning candle, glass jar and a mint leaf. • Jan Ingenhousz – same as Priestly except showed that light was required.

  24. Photosynthesis Equation

  25. Photosynthesis-Chemical Equation • Reactants: carbon dioxide & water • Products: Glucose and oxygen gas • Also: Light energy, enzymes, pigments

  26. Another Perplexing Question about Photosynthesis • Where does the oxygen released by photosynthesis come from directly? Does it come from the carbon dioxide or water? • First challenged by Challenged by C.B. Van Niel using photosynthetic bacteria which showed that CO2 is not split. • Isotopic Oxygen (18O) was used to trace and track the fate of oxygen.

  27. Tracking the Fate of Isotopic Oxygen

  28. Photosynthesis: an overview Redox process H2O is split into: 2e- and 4 H+ The H’s are transferred to CO2 and a sugar is produced (CH2O) 2 Major steps to Photosynthesis: • Light Reactions(“photo”) -occurs in the thylakoids • Dark Reactions -Also called “Carbon fixation” -occurs in the stroma -Involves the Calvin Cycle

  29. Photosynthesis: an overview

  30. A Photosystem (located in the thylakoid membranes) • Light Harvesting Protein Pigments • Have “antennae pigments complexes” (200-300 pigment molecules) • Chlorophyll a and chlorophyll b are present • Chlorophyll a = Reaction Center • Primary Electron Acceptor will receive the electron (reduced) and chlorophyll a will be oxidized and lose the electron.

  31. Structure of a Photosystem • Light harvesting units of the thylakoid membrane • Composed mainly of protein and pigment antenna complexes • Antenna pigment molecules are struck by photons • Energy is passed to reaction centers (redox location) • Excited e- from chlorophyll is trapped by a primary e- acceptor

  32. Photosystems in the Thylakoid Membrane

  33. Mechanical view of Photosynthesis

  34. Build up of Hydrogen ions in the thylakoid space

  35. Introductory Questions #9 • Name three factors that can affect transpiration in plants. • How do plants absorb light energy? Name some features that allow plants to absorb light. What are some differences between chlorophyll a and chlorophyll b? • What did Engelmann’s experiment measure? What organisms did he use? • Which reactant does the oxygen produced from photosynthesis directly come from? • Where specifically do the light and dark reaction take place within a plant cell? • Name the three parts that make up a photosystem. • How does NADPH differ from NADH?

  36. Photosystems in the Thylakoid Membrane

  37. Noncyclic Electron Flow

  38. Noncyclic Electron Flow • Most common light reaction pathway • Involves (2) Photosystems: Photosystem II (P680)-absorption peak Photosystem I (P700)-absorption peak • Exhibits A “Z scheme” or Zig-Zag flow of electrons • Electrons flow in one direction • ATP and NADPH are produced • Electrons do not cycle back to the ground state to chlorophyll.

  39. Cyclic Electron flow • Alternative cycle when ATP is deficient • Photosystem I used but not II; produces ATP but no NADPH • Why? The Calvin cycle consumes more ATP than NADPH……. • Cyclic photophosphorylation Review of Light reactions: http://web.mit.edu/esgbio/www/ps/light.html

  40. Cyclic Electron flow

  41. Cyclic Flow of Electrons • Utilizes Photosystem I (P700) only • Electrons cycle back to chlorophyll • NADPH is not produced. • Helps to produce more ATP that is used in the Calvin Cycle • Stimulated by the accumulation of NADPH

  42. Photosynthesis-Light & Dark Reactions

  43. The Calvin Cycle-C3 pathway 3 molecules of CO2 are ‘fixed’ into glyceraldehyde 3-phosphate (G3P) 3 Phases: 1- Carbon fixation Each CO2 is attached to RuBP (rubisco enzyme) 2- Reduction electrons from NADPH reduces to G3P; ATP used up 3- Regeneration G3P rearranged to RuBP; ATP used; cycle continues

  44. The Calvin Cycle-C3 pathway

  45. Calvin Cycle: First Phase Carbon Fixation: (1 carbon) + (5 carbon) (3 carbon) CO2 + Ribulose Bisphosphate (RuBP) →2 Phosphoglycerate (PGA) w/ help of: RUBISCO (Ribulose Bisphosphate Carboxylase)-most abundant protein on earth **Carbon is converted from an inorganic form into an organic form and thereby “FIXED”. **A Total of Six carbons must be fixed for one glucose molecule or some other hexose.

  46. Calvin Cycle: Second Phase Reduction Phase: Phosphoglycerate (PGA) ↓ is phosphorylated (use ATP) 1,3-bisphosphoglycerate ↓ Redox Rxn w/NADPH Glyceraldehyde-3-Phosphate (G3P) *G3P is a sugar also seen in glycolysis *For every 3 CO2→ 6 G3P is produced but only ONE can be counted as a gain in carbohydrate and can exit the cycle.

  47. Calvin Cycle: Third Phase Regeneration of RUBP: 5 G3P are phosphorylated  3 RuBP 3 ATP’s are used to do the chemical rearrangement RuBP can now accept more CO2 molecules

  48. Calvin Cycle - Net Synthesis • For every G3P molecule produced: 3 CO2 are brought in 9 ATP’s are consumed 6 NADPH are used **G3P can then be used by the plant to make glucose and other organic compounds Website for review of the Calvin Cycle: http://web.mit.edu/esgbio/www/ps/dark.html

  49. To Make a Six Carbon Molecule You need: • 6 CO2 molecules (6 carbons) • 6 molecules of RuBP (30 carbons) (remain in the cycle from TEN G3P’s) • 18 ATP molecules -Produced- • 12 molecules of PGA (36 carbons) • 2 molecules of G3P (6 carbons)

  50. C3 Metabolic Pathway in Plants • CO2 enters directly into the Calvin Cycle • The first organic compound made is a 3 carbon molecule called PGA (phosphoglycerate) • Close their stomata on hot, dry days to conserve water. • Photorespiration occurs typically in these plants. • Examples include: Rice, Wheat, and Soybeans.