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PHOTOSYNTHESIS

PHOTOSYNTHESIS. WEEK 9 Text pages 117-132 (CHAPTER 7). How do plants respire?. PHOTOSYNTHESIS!!. The sun is the source of energy for producing carbohydrates in plants Energy flow occurs through a series of electron transfers and oxidation

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PHOTOSYNTHESIS

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  1. PHOTOSYNTHESIS WEEK 9 Text pages 117-132 (CHAPTER 7)

  2. How do plants respire? PHOTOSYNTHESIS!!

  3. The sun is the source of energy for producing carbohydrates in plants Energy flow occurs through a series of electron transfers and oxidation reduction reactions in the chloroplasts of plant cells

  4. Photosynthesis v Cell Respiration Cell Respiration -Cristae -ETC in cristae energized by glucose e- -H+ electrochemical gradient -Citric Acid Cycle -NADH Photosynthesis -Thylakoid discs -ETC in thylakoid energized by sun -H+ electrochemical gradient -Calvin Cycle -NADPH ETC= Electron Transport Chain

  5. Photosynthesis • Process of converting solar energy into chemical energy (carbohydrates) • Organisms that produce their own food = autotrophs • Autotrophs are producers- synthesize carbohydrates • Heterotrophsare consumers • Autotrophsandheterotrophsuse carbs. synthesized by photosynthesis

  6. PHOTOSYNTHESIS SOLAR ENERGY CO2 + 2H2O (CH2O)+ H2O + O2 CHEMICAL ENERGY OXYGEN IS RELEASED DURING PHOTOSYNTHESIS CARBON DIOXIDE IS REDUCED AND WATER IS OXIDIZED REDUCTION- Gain Hydrogen/electrons OXIDATION- Lose Hydrogen/electrons REDOX

  7. SOLAR ENERGY CO2 + 2H2O (CH2O)+ H2O + O2 x 6 SOLAR ENERGY 6CO2 + 6H2O C6H12O6+ 6H2O + 6O2 GLUCOSE

  8. SOLAR ENERGY • Solar energy is converted to ATP molecules • ATP is used to REDUCECO2 into carbohydrates • Therefore, solar energy is not used directly

  9. Simplified REDOXRxn.-Photosynthesis

  10. PHOTOSYNTHESIZERS • Plants • Algae • Bacteria • Cyanobacteria • Blue/green “algae” Eukaryotes Eukaryotes Prokaryotes

  11. Importance of Photosynthesizers • Provide oxygen to sustain life! • O2 rises into atmosphere where it later becomes OZONE (O3) which filters out harmful rays • Plant fossils  coal, a “fossil fuel” • Fermentation of plant materials  ethanol (gasoline additive) • Lumber • Fabrics (cotton) • Paper • Pharmaceuticals • Beauty products • Plants are simply incredible !!

  12. How/Where does Photosynthesis occur? • The green portion of plants absorbs sunlight • CO2 enters plant leaf via small openings = STOMATA • Rootsof plant absorb H2O • CO2 andH2O diffuse into CHLOROPLAST • Photosynthesis occurs in chloroplasts

  13. CHLOROPLASTS • Are organelles • Located inside of plant cells • Are surrounded by a double membrane • Semi-fluid interior = STROMA • The STROMA contains THYLAKOIDS • THYLAKOIDS are membrane bound sacs • THYLAKOIDS are the site of light dependent reactions • THYLAKOIDS stack on top of each other to form GRANA • THYLAKOIDS are connected to the space of all other thylakoids inside of the chloroplast which forms an inner compartment = THYLAKOID SPACE http://sciencephoto.com/images/download_lo_res.html?id=670012430

  14. Fig. 7.2 pg. 119

  15. CHLOROPHYLL • Found in the THYLAKOIDMEMBRANE • Is a green pigment • Is a molecule • Absorbs solar energy Chlorophyll a

  16. Absorption of solar energy occurs at the THYLAKOID membrane/ GRANA CO2 is reduced by enzymes to a carbohydrate in the STROMA

  17. How is CO2 reduced to form a Carbohydrate? • Electrons are needed to reduce CO2 • NADPH= nicotinamide adenine dinucleotide phosphate-oxidase • NADP+ is the coenzyme of the REDOXrxn. REDUCTION OF NADP+ NADP+ + 2e- + H+ NADPH

  18. PHOTSYNTHESIS TWO sets of reactions 1- THE LIGHT REACTIONS 2- THE CALVIN CYCLE REACTIONS

  19. Light Reactions • Only occur during daylight hours • Solar energy is used to energize electrons involved in the electron transport chain • As electrons move from complex to complex, energy is released • ATP is produced via the movement of electrons and release of energy as they move down the electron transport chain • Energized electrons are taken up by NADP+

  20. Light Reactions SOLAR ENERGYCHEMICAL ENERGY (ATP and NADPH)

  21. CALVIN CYCLE REACTIONS • Named for Melvin Calvin (nobel prize recipient) • CO2is taken up and then reduced to a carbohydrate that is later converted to glucose • The ATP and NADPH from the light reaction are used to REDUCECO2

  22. CALVIN CYCLE REACTIONS CHEMICAL ENERGY CHEMICAL ENERGY (ATP and NADPH) (Carbohydrate)

  23. Overview of Photosynthesis SOLAR ENERGYCHEMICAL ENERGY CHEMICAL ENERGY ATP and NADPH Carbohydrate

  24. Steps of PHOTOSYNTHESIS 1- SOLAR ENERGY is absorbed by the THYLAKOID/ GRANA 2- H2O is split and O2 is released 3- ATP and NADPH are produced 4- CO2 is taken up at the STOMATA 5- CO2 is reduced to carbohydrate (CH2O) using ATP and NADPH from the light rxns. Light Rxn. Calvin Cycle Rxn.

  25. Light is absorbed by the THYLAKOID/ GRANACarbon Dioxide enters the chloroplast via the STOMATAThe Calvin Cycle occurs in the STROMA

  26. Visible Light/Absorption Spectrum • Visible light- ROYGBIV • Visible light is most prevalent in the environment • Ozone (O3) protects us from high energy wave lengths • Chloroplast pigments absorb only some wavelengths within their absorption spectrum • Chlorophyll a and b are important in photosynthesis and absorb, violet, blue and red light • Green light is transmitted and reflected by chlorophyll, therefore plants appear green to us • All light reflected = white • All light absorbed = black • Reflection of a particular color= the color you see !!

  27. Fig. 7.6- pg. 122 CAROTENOIDS- pigment molecules in plants that give shades of yellow and orange (fall foliage colors) by absorbing violet-blue-green

  28. The Light ReactionsA Detailed View Begins with Photosystem II (PSII) Photosystem- contains: 1- pigment complex (chlorophyll a, b and carotenoids) 2- An electron acceptor moleule w/in the THYLAKOID memebrane During the light rxn., electrons follow a NONCYCLIC pathway beginning at PSII

  29. Fig. 7.7 pg. 123 1. • Solar Energy is captured by PSII • H20is split, releases electrons and O2 • Electrons are passed to PSII • Electrons concentrate at the Reaction Center located in chlorophyll a • The Reaction Center “energizes” the e- • The e- are accepted by and e- acceptor 6. 4./5. 3. 2. Water is oxidized, O2 is released (Mito.) Hydrogen stays in thylakoids to create H+ gradient

  30. 7. Electrons move along the electron transport • chain and H+ forms a gradient by staying in the • Thylakoid space. • ATP is produced when H+ ions go through the ATP • Synthase complex. ATP is used in the Calvin Cycle to • reduce CO2 to carbohydrates • Solar energy is absorbed by PSI • Excited electrons are captured by the electron acceptor • (low energy electrons from the ETC are captured by PSI and • are then “excited” by the electron acceptor • 2 electrons from PSI are passed to NADP+ • A hydrogen ion is also added to NADP+ which gets REDUCED • to NADPH • 12. NADPH is used in the Calvin Cycle along with ATP 10. 11. 9. 7./8. 12. ATP

  31. THE THYLAKOID MEMBRANE Fig. 7.8 pg. 124

  32. The Light Reaction Review • Occurs in the THYLAKOID MEMBRANE • Inputs= Water and Sunlight • Involves PS II, the electron transport chain and PSI • ATP is produced via the ETC and CHEMIOSMOSIS • NADPH is produced via the reduction of NADP+ via electrons released from PSI • Electrons from the ETC ‘feed’ PSI • END PRODUCTS OF LIGHT RXN = ATP and NADPH

  33. The Calvin Cycle Reactions • A series of reactions that occur in the STROMA of chloroplasts • Uses CO2 from the atmosphere to produce carbohydrates • CO2 is reduced using ATP and NADPH to form carbohydrates

  34. STEPS of the CALVIN CYCLE 1- Carbon Dioxide fixation - CO2 from atmosphere attaches to RuBP (ribulose-1,5-bisphosphate), a 5-Carbon molecule  a 6-C molecule  splits into TWO 3-C molecules (3PG- 3-Phosphoglycerate) - This rxn. is sped up by RuBPcarboxylase(enzyme) 2- CO2reduction 3- Regeneration of RuBP

  35. RuBP is used And regenerated In the cycle Fig. 7.9 pg. 126

  36. 2. CO2 REDUCTION Fig. pg. 127 From the light Rxns. G3P is also known as PGAL G3P is END PRODUCT of Calvin Cycle

  37. 3.Regeneration of RuBP

  38. G3P (Glyceraldehyde-3-Phosphate) G3P is the end product of the Calvin Cycle G3P can be converted into other molecules G3P Amino Acid Synthesis Fatty Acid Synthesis Glucose Phosphate Plant oils STARCH (Storage form of glucose) + Fructose Phosphate Plants use sucrose to transport carbohydrates from one part of the plant to the other (Structural carbohydrate) CELLULOSE SUCROSE

  39. Calvin Cycle Review • The Cycle begins when CO2 from the atmosphere enters the chloroplasts via the STOMATA of the leaves • CO2 is fixed by RuBP to form TWO3-Carbon molecules called 3PG • CO2 is reduced via the oxidation of ATP and NADPH (from the light cycle) to form G3P • G3P is converted into other organic molecules (glucose, sucrose, cellulose, starch, amino acids, fatty acids) • RuBPis regenerated • G3Pis the end product of the Calvin Cycle

  40. OTHER TYPES OF PHOTOSHYTHESIS • C3 Photosynthesis • Normally, C3 plants use RuBPCarboxylasefollowing CO2fixation to form Two 3PG molecules in mesophyll cells • Stomata open and close to regulate the influx of CO2 • When stomata close (hot days), O2 increases due to photosynthesis  RuBP combines with O2with the help RuBPcarboxylaseinstead of CO2  only 1 molecule of 3PG is produced along w/phosphoglycolate(a toxic 2-Carbon molecule) andCO2 is released = PHOTORESPIRATION • PHOTORESPIRATON is not efficient and is wasteful and is not part of the Calvin Cycle!! Yields 1 3PG molecule And 1 Phosphoglycolate molecule (TOXIC!)

  41. OTHER TYPES OF PHOTOSHYTHESIS • C4 Photosynthesis - Contain bundle sheath cells and mesophyll cells (both contain chloroplasts) - The mesophyll cells are arranged concentrically around the bundle sheath cells - C4 plants use enzyme PEP carboxylase(PEPCase) to fix CO2and PEP (phosphoenolpyruvate)  OXALOACETATE -Oxaloacetate is then reduced to malate in mesophyll cells which pump malate and CO2 into the bundle sheath cells - CO2 then enters the Calvin Cycle in the bundle sheath cells -C4 plants avoid photorespiration!! (sugarcane, corn, bermuda grass- evolved in high temps) WHY? • B/c PEPCase does not bind with O2! CO2 is able to go to the Calvin Cycle • CO2 is not able to go to the Calvin Cycle in C3 plants when they shut their Stomata!

  42. Even when STOMATA are closed, CO2 is delivered to the Calvin Cycle in C4 plants

  43. The C4 Pathway

  44. Why are C4 Plants able to continue on with the Calvin Cycle even when their Stomata are closed? Which came first evolutionarily, C3 or C4 plants?

  45. OTHER TYPES OF PHOTOSHYTHESIS • CAM Photosynthesis “Crassulacean-acid Metabolism” -CAM photosynthesizerspartition rxns. based on time of day -Only open stomata at night! (conserves Water) -At night, CAM plants use PEPCase to fix some CO2 to form 4-C molecules (malate) -Malate is stored in plant vacuoles in mesophyll cells - During the day, the malate releases CO2 to the Calvin Cycle when ATP and NADPH are available from the light rxns. -CAM plants are able to live in stressful conditions! CAM occurs in flowering plants and various other plant groups

  46. Types of CAM Plants Family Familiar Names

  47. Plants: An Evolutionary Perspective Plants have adapted to their environment over thousands of years First land plants evolved approx. 430-440 mya Each type of photosynthesis has its advantages and disadvantages C4 plants most likely evolved in areas of high light intensities, high temps and little rainfall and are more sensitive to cold C3 plants function better than C4 plants below 25 degrees Celcius. CAM plants copete well with either type of plant in arid (lack of water) environments

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