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AP Biology John D. O’Bryant School of Mathematics and Science

AP Biology John D. O’Bryant School of Mathematics and Science

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AP Biology John D. O’Bryant School of Mathematics and Science

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  1. AP BiologyJohn D. O’Bryant School of Mathematics and Science November 8, 2012

  2. Agenda • Do Now (Table of Contents) • HW discussion • Photosynthesis: Modeling • Quiz

  3. Table of Contents (Notes/Classwork)

  4. HW

  5. Modeling Photosynthesis Task: In pairs, build a dynamic model of C3 photosynthesis using cutout pieces of paper to represent the molecules, ions, and membrane transporters or pumps. You should be able to manipulate or move carbon dioxide and water and its breakdown products through the various steps of the process.

  6. Quiz • 1. The end products of the light-dependent reactions of photosynthesis are • A)ADP, H2O, NADPH2 • B)ADP, PGAL, RuBP (RuDP) • C)ATP, CO2, H2O • D)ATP, NADPH2, O2 • E)CO2, H+, PGAL

  7. Quiz • 2. Which of the following enzymes is responsible for CO2 fixation in C3 plants? • A) Succinate dehydrogenase • B) RuBP (RuDP) carboxylase • C) Hexokinase • D) Amylase • E) DNA polymerase

  8. Quiz • 3. All of the following statements about a chloroplast and a mitochondrion are true EXCEPT: • A) Both use proton gradients for energy production. • B) Both capture light energy. • C) Both contain DNA. • D) Both are bound by two unit membranes. • E) Both synthesize ATP.

  9. Quiz • 4. If plants are grown for several days in an atmosphere containing 14CO2 in place of 12CO2, one would expect to find • A)very little radioactivity in the growing leaves • B)large amounts of radioactive water releasedfrom the stomates • C)a large increase in 14C in the starch stored in theroots • D)a large decrease in the rate of carbon fixation inthe guard cells • E)an increase in the activity of RuBP carboxylasein the photosynthetic cells

  10. Quiz • 5. The O2 released during photosynthesis comes from • A) CO2 • B) H2O • C) NADPH • D) RuBP (RuDP) • E) C6H12O6

  11. Quiz • 6. Which of the following is an important difference between light-dependent and light-independent reactions of photosynthesis? • A) The light-dependent reactions occur only during the day; the light-independent reactions occur only during the night. • B) The light-dependent reactions occur in the cytoplasm; the light-independent reactions occur in chloroplasts. • C) The light-dependent reactions utilize CO2 andH2O; the light-independent reactions produceCO2 and H2O. • D) The light-dependent reactions depend on the presence of both photosystems I and II; the light-independent reactions require only photosystem I. • E) The light-dependent reactions produce ATP and NADPH; the light-independent reactions use stored energy in ATP and NADPH.

  12. Quiz • 7. Carbohydrate-synthesizing reactions of photosynthesis directly require • A) light • B) products of the light reactions • C) darkness • D) O2 and H2O • E) chlorophyll and CO2

  13. Quiz • 8. All of the following could reduce the yield of photosynthetic products EXCEPT • A) lower concentrations of carbon dioxide in the atmosphere • B) increased photorespiration • C) reduced carbon dioxide concentrations inthe air spaces of the leaf • D) increased frequency of stomata openings • E) fewer Calvin cycle enzymes

  14. Quiz • 9. All of the following are common to C3 and C4 photosynthesis EXCEPT • A) Photolysis • B) Initial step of CO2 fixation • C) Cyclic photophosphorylation • D) Noncyclic photophosphorylation • E) Chemiosmotic phosphorylation

  15. Photosynthesis:Variations on the Theme

  16. O C O Remember what plants need… • Photosynthesis • light reactions • light • H2O • Calvin cycle • CO2  sun  ground air What structures have plants evolved to supply these needs?

  17. xylem (water) phloem (sugar) cuticle epidermis palisades layer spongy layer stomate guardcell vascular bundle Leaf Structure O2 H2O CO2 Transpiration O2 H2O CO2 Gas exchange

  18. Controlling water loss from leaves • Hot or dry days • stomates close to conserve water • guard cells • gain H2O = stomates open • lose H2O = stomates close • adaptation to living on land, but… creates PROBLEMS!

  19. O2 CO2 H2O O2 CO2 When stomates close… • Closed stomates lead to… • O2 build up  from light reactions • CO2 is depleted  in Calvin cycle • causes problems in Calvin Cycle The best laidschemes ofmice and men…and plants! xylem (water) phloem (sugars)  

  20. Inefficiency of RuBisCo: CO2 vs O2 • RuBisCo in Calvin cycle • carbon fixation enzyme • normally bonds Cto RuBP • CO2 is the optimal substrate • reduction of RuBP • building sugars • when O2 concentration is high • RuBisCo bonds Oto RuBP • O2 is a competitive substrate • oxidation of RuBP • breakdown sugars photosynthesis photorespiration

  21. 1C 5C 3C CO2 RuBP 5C 6C unstable intermediate ATP ADP 3C ATP PGA ADP G3P 3C NADPH NADP Calvin cycle when CO2 is abundant RuBisCo G3P to make glucose C3 plants

  22. O2 RuBP 5C 3C 2C to mitochondria ––––––– lost as CO2 withoutmaking ATP Calvin cycle when O2 is high Hey Dude, are you highon oxygen! RuBisCo It’s so sad to see agood enzyme,go BAD! photorespiration

  23. Impact of Photorespiration • Oxidation of RuBP • short circuit of Calvin cycle • loss of carbons to CO2 • can lose 50% of carbons fixed by Calvin cycle • reduces production of photosynthesis • no ATP (energy) produced • no C6H12O6 (food) produced • if photorespiration could be reduced, plant would become 50% more efficient • strong selection pressure to evolve alternative carbon fixation systems

  24. Reducing photorespiration • Separate carbon fixation from Calvin cycle • C4 plants • PHYSICALLY separate carbon fixation from Calvin cycle • different cells to fix carbon vs. where Calvin cycle occurs • store carbon in 4C compounds • different enzyme to capture CO2 (fix carbon) • PEP carboxylase • different leaf structure • CAM plants • separate carbon fixation from Calvin cycle by TIME OF DAY • fix carbon during night • store carbon in 4C compounds • perform Calvin cycle during day

  25. C4 plants • A better way to capture CO2 • 1st step before Calvin cycle, fix carbon with enzymePEP carboxylase • store as 4C compound • adaptation to hot, dry climates • have to close stomates a lot • different leaf anatomy • sugar cane, corn, other grasses… corn sugar cane

  26. O2 CO2 PEP (3C) + CO2 oxaloacetate (4C) C4 leaf anatomy light reactions PEPcarboxylase C3 anatomy bundlesheathcell CO2 stomate RuBisCo • PEP carboxylase enzyme • higher attraction for CO2 than O2 • better than RuBisCo • fixes CO2 in 4C compounds • regenerates CO2in inner cells for RuBisCo • keeping O2 away from RuBisCo C4 anatomy

  27. Comparative anatomy Location,location,location! C3 C4 PHYSICALLY separate C fixation from Calvin cycle

  28. CAM (Crassulacean Acid Metabolism) plants • Adaptation to hot, dry climates • separate carbon fixation from Calvin cycle by TIME • close stomates during day • open stomates during night • at night: open stomates & fix carbonin 4C “storage” compounds • in day: release CO2 from 4C acids to Calvin cycle • increases concentration of CO2 in cells • succulents, some cacti, pineapple It’s all inthe timing!

  29. CAM plants cacti succulents pineapple

  30. C4 vs CAM Summary solves CO2 / O2 gas exchangevs. H2O losschallenge CAM plants separate 2 steps of C fixation temporally =2 different times night vs. day C4 plants separate 2 steps of C fixation anatomically in 2 different cells

  31. We’ve all gotbaggage! Why the C3 problem? • Possibly evolutionary baggage • Rubisco evolved in high CO2 atmosphere • there wasn’t strong selection against active site of Rubisco accepting both CO2 & O2 • Today it makes a difference • 21% O2 vs. 0.03% CO2 • photorespiration can drain away 50% of carbon fixed by Calvin cycle on a hot, dry day • strong selection pressure to evolve better way to fix carbon & minimize photorespiration

  32. It’s not so easy as it looks… Any Questions??

  33. Ghosts of Lectures Past(storage)

  34. O2 CO2 H2O O2 CO2 A second look inside a leaf… • Gas exchange & water flow • CO2 in  • O2 out  • H2O out  for Calvin cycle waste from light reactions for light reactions photosynthesis xylem (water) phloem (sugars) gas exchangewater loss

  35. CO2 O2 O2 CO2 C4 photosynthesis PHYSICALLY separated C fixation from Calvin cycle • Outer cells • light reaction & carbon fixation • pumps CO2 to inner cells • keeps O2 away from inner cells • away from RuBisCo • Inner cells • Calvin cycle • glucose to veins

  36. Supporting a biosphere • On global scale, photosynthesis is the most important process for the continuation of life on Earth • each year photosynthesis… • captures 121 billion tons of CO2 • synthesizes 160 billion tons of carbohydrate • heterotrophs are dependent on plants as food source for fuel & raw materials

  37. air The poetic perspective… • All the solid material of every plantwas built by sunlight out of thin air • All the solid material of every animal was built from plant material sun Then all the plants, cats, dogs, elephants & people …are really particles of air woven together by strands of sunlight!

  38. If plants can do it…You can learn it! Ask Questions!!

  39. Plant pigment lab