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Chapter 10

Chapter 10. Photosynthesis. Modes of Nutrition. Heterotrophs – obtain organic compounds by consuming other organisms (animals) Photoautotrophs – build organic compounds with light energy (plants)

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Chapter 10

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  1. Chapter 10 Photosynthesis

  2. Modes of Nutrition • Heterotrophs – obtain organic compounds by consuming other organisms (animals) • Photoautotrophs – build organic compounds with light energy (plants) • Chemoautotrophs – use inorganic substances (sulfur, ammonia)as an energy source to make organic compounds (some bacteria)

  3. Photosynthesis Opposite of Cellular Respiration! NET: But really..

  4. Photosynthetic prokaryotes do not have chloroplasts. Chlorophyll is in their plasma membrane. Contains chlorophyll

  5. Light Dependent: Closer Look • Sunlight is electromagnetic energy • Wave-like properties and Particle-like properties • Waves  Wavelengths • Visible wavelengths = 380nm-750nm • Pigments: Substances that absorb visible light • Chlorophyll ais main pigment • Accessory Pigments: • Chlorophyll b(yellow-green • Carotenoids(oranges, yellows) So, why do leaves look green?

  6. Lab #4 – Plant Pigments

  7. What wavelengths are absorbed Effectiveness of wavelengths = activity • Doesn’t exactly match due to accessory pigments (transfer energy to Chlor. a)

  8. Light Dependent: Photosystems • 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 • Excited e- from chlorophyll is trapped by a primary e- acceptor

  9. Light Dependent: Photosystems • 2 photosystems in thylakoid membrane • Photosystem II • chlorophyll a • P680 = absorbs 680nm ~ red light • Photosystem I • chlorophyll b • P700 = absorbs 700nm ~ red light

  10. Light Dependent = The ETC • ETC uses light energy to produce • ATP & NADPH • go to Calvin cycle • PS II absorbs light • excited electron passes from chlorophyll to “primary electron acceptor” • need to replace electron in chlorophyll • enzyme extracts electrons from H2O & supplies them to chlorophyll • splits H2O • O combines with another O to form O2 • O2 released to atmosphere • and we breathe easier!

  11. Fill in Stroma (fluid) Thylakoid (disk)

  12. Lab #4 - Photosynthesis • DPIP was used to replace NADP+ • DPIP accepted e- (reduced = RIG) • Turned from Blue  Clear • More light could pass through cuvette • Transmittance % increased

  13. Light Dependent: Photophosphorylation • Using light energy to add a P to ADP • Two types: • Non-Cyclic • Cyclic

  14. Non-Cyclic Photophosphorylation • Light reactions elevate electrons in 2 steps (PS II & PS I) • PS II generates energy as ATP • PS I generates reducing power as NADPH • NADPH used in Calvin Cycle (light independent)

  15. Cyclic Photophosphorylation • Involves only PS1 • Generates ATP but no NADPH or O2 • Supplements the ATP supply required for the Calvin Cycle

  16. Light Independent: A Closer Look • AKA The Calvin Cycle • In stroma • Uses ATP and NADPH to convert CO2 to sugar • Makes a 3-C sugar • Needs 3 CO2 to make 1 Glucose (C6H12O6) • Uses 18 ATP (endergonic) and 12 NADPH to make 1 Glucose

  17. G3P • Glyceraldehyde-3-P • end product of Calvin cycle • energy rich 3 carbon sugar “C3 photosynthesis” • G3Pis an important intermediate • G3P  glucose   carbohydrates   lipids  phospholipids,fats, waxes   amino acids  proteins   nucleic acids  DNA, RNA

  18. RuBisCo • Enzyme which fixes carbon from air • ribulosebisphosphatecarboxylase • CO2 + 5-C sugar (RuBP) is broken down by RuBisCo into 3-C sugars • most abundant enzyme

  19. Types of Plants • C3 - most plants, produce G3P • Ex: rice, wheat, soybeans • Occurs in a single chloroplast • CO2 + RuBp (5-C) = 6-C  split into G3Ps  Glucose

  20. Ruh-Roh… • Hot, dry days • Stomata close to conserve water • CO2 is depleted  • O2 builds up from light reactions • RuBisCo • when O2 concentration is high • RuBisCo bonds OtoRuBP • O2 is a competitive substrate • oxidation of RuBP • breakdown sugars CALLED PHOTORESPIRATION!

  21. Photorespiration • Consumes oxygen • Makes carbon dioxide • Produces no ATP • Decreases photosynthetic output (decreases organic molecules used in Calvin Cycle)

  22. SOLUTIONS! • Plants living in hot, arid climates have evolved different modes of carbon fixation • C4 and CAM plants

  23. FYI: the PEP Carboxylase has a much greater affinity for CO2 than RuBisCo at higher temps • C4 – turn CO2 into a 4-C compound • Ex: corn, sugarcane • Favored in hot, arid environments • 2 chloroplasts • Mesophyll = CO2 is fixed into a 4-C • Bundle Sheath Cells (cells surrounding veins) = Calvin Cycle • Facilitates production of CO2 to combat photorespiration

  24. CAM Plants • Ex: Cacti, Pineapple • Very arid environments • At night: Stomata open, take in CO2 • Store a 4-C compound in vacuole • During Day: Light Rxns supply ATP and NADPH, Uses stored CO2 to complete Calvin Cycle

  25. Photosynthesis Summary • Light reactions • produced ATP • produced NADPH • consumed H2O • produced O2as byproduct • Calvin cycle • consumed CO2 • produced G3P (sugar) • regenerated ADP • regenerated NADP

  26. Interdependence in Nature

  27. REDOX rxns Cell Respiration Photosynthesis Endergonic Energy is REQUIRED Light is the energy source that moves e- Water is split, electrons are moved from water to carbon dioxide CO2 is reduced Makes sugar (glucose) • Exergonic • Energy is RELEASED from the oxidation of sugar • Electrons are transported to OXYGEN = Water • Oxygen pulls e -s down to produce concentration gradient of H + • H+ is pumped through ATP Synthase ADP + Pi = ATP

  28. Photosynthesis Animation • http://dendro.cnre.vt.edu/forestbiology/photosynthesis.swf

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