1. Photosynthesis http://www.ualr.edu/~botany/photosynthrxns.gif

2.  Light is central to the life of a plant  Photosynthesis is the most important chemical process on Earth  It provides food for virtually all organisms  Plant cells convert light into chemical signals that affect a plant’s life cycle Life in the Sun

4. Definitions  Photosynthesis  The conversion of light energy to chemical energy that is stored in glucose or other organic compounds  Occurs in plants, algae, and certain prokaryotes.

5.  Autotrophs:  Greek meaning autos=self; trophos=feed.  Not totally self-sufficient.  Self feeders in the sense that they sustain themselves without eating other organisms.  Produce their own organic molecules.  Only require CO2, and H20.  Heterotrophs:  Other feeders  Unable to make their own food  Consumers

6. Leaves and Leaf Structure   The Raw Materials of Photosynthesis Enter the Cells of the Leaf  Water and Carbon Dioxide   The Products of Photosynthesis Leave the Leaf  Sugar and Oxygen

7. The Chloroplast:

8. Chloroplast  Organelle  Location of Photosynthesis http://www.lclark.edu/~seavey/Bio100_03/Lecture%20notes/lecture_Feb_11.h tml

9. Chloroplasts  Thylakoids:  Membranous system, arranged into flattened sacs.  Grana:  Thylakoids are stacked like poker chips, forming these structures.  Stroma:  The fluid outside the Thylakoid. http://www.wellesley.edu/Biology/Courses/Plant/chloro.html

12. The Chloroplast:

13. Chlorophyll and Accessory Pigments All Photosynthetic Organisms Have Chlorophyll A  Accessory Pigments Absorb Energy that Chlorophyll a Does not Absorb  Chlorophyll b  Xanthophylls  Carotenoids (Beta-Carotene) http://www.nyu.edu/pages/mathmol/library/photo/

14. Chlorophyll and Accessory Pigments  If a Pigment Absorbs Light Energy, 1 of 3 Things Will Occur  1)Energy Is Dissipated as Heat  2)The Energy may Be Emitted Immediately as a Longer Wavelength (a Phenomenon Known as Fluorescence)  3)Energy may Trigger a Chemical Reaction, as in PS http://www.ualr.edu/~botany/chlorophyll.jpg

15. Energetics of Visible Light Red is less energetic Violet is more energetic

16. Why Plants are Green?

17. Nature of Light  When Light Hits an Object, 3 Possibilities  Absorbed by Object  Reflected off Object  Transmitted through Object  Colors We See Are actually Light Reflected from an Object  Something that Appears Green Is Reflecting Green Light and either Absorbing or Transmitting the other Wavelengths  Plants Reflect Green, but Absorb other Wavelengths for Use in PS

18. Nature of Light  Red and Blue Wavelengths most Important for PS  Captured by Chloroplasts and Used to Initiate PS Reactions http://faculty.concord.edu/rockc/intro/sensate.htm

20. Photosynthetic Reactions  Overall Equation  Simplified

21. Light Reactions  Electron Transfer  When Light Strikes Magnesium (Mg) Atom in Center of Chlorophyll Molecule, the Light Energy Excites a Mg Electron and It Leaves Orbit from the Mg Atom  The Electron Can Be Converted to Useful Chemical Energy http://www.sirinet.net/~jgjohnso/lightreactionproject.html

24. Light Reactions  All of the pigments are able to “gather” light, but they are not able to “excite” the electrons. Only one special molecule—located in the reaction center is capable of transforming light energy to chemical energy.  So the pigments harness the light energy and then pass it on to the reaction center. http://www.sirinet.net/~jgjohnso/lightreactionproject.html

25.  The production of ATP by chemiosmosis in photosynthesis Figure 7.9 Thylakoid compartment (high H + ) Thylakoid membrane Stroma (low H + ) Light Antenna molecules Light ELECTRON TRANSPORT CHAIN PHOTOSYSTEM IIPHOTOSYSTEM IATP SYNTHASE

26. Photosynthesis  Photosynthesis has 2 stages:  1) Light Reactions  Requires Light to Occur  Involves the Actual Harnessing of Light Energy  Occur in\on the Thylakoid  Cyclic & Non-Cyclic  2) Dark Reactions(Calvin Cycle)  Does not Need Light to Occur  Involve the Creation of the Carbohydrates  Products of the Light Reaction Are Used to Form C-C Covalent Bonds of Carbohydrates  Occur in the Stroma http://www.daviddarling.info/images/chloroplast.jpg

27.  The complete process of photosynthesis consists of two linked sets of reactions:  the light reactions (the ‘photo’ part)  and the Calvin cycle (the ‘synthesis’ part)  The light reactions convert light energy into chemical energy and produce O 2  The Calvin cycle assembles sugar molecules from CO 2 using the high energy products of the light reactions Overview:

28. Non-Cyclic Electron Flow

29.  Predominant Route for Electrons.  1) Photosystem II (Second photosystem to be discovered) absorbs light. An electron is excited to a higher energy level in the reaction center (P680). Absorbs the 680 light wavelength spectrum.  2) Electrons are extracted from water and gives them to P680. When the 2 H’s and O is split, the O immediately combines with another one and makes O2(oxygen).

31. Non-Cyclic Electron Flow  3) The excited electrons from Photosystem II get passed on to Photsystem I via an electron transport chain (ETC).  4) As electrons cascade down he chain to a lower energy level, ATP is produced when it goes through the thylakoid membrane. This is called photophosphorylation because its driven by light. The ATP generated by the light reaction will be used to synthesize sugars in the Calvin Cycle, the second stage of photosynthesis.

32. Non-Cyclic Electron Flow

33.  5) When the electron reaches the bottom of the ETC, it fills an electron hole in P700 of Photosystem I (Absorbs 700nM light wavelength). Photosystem 1 was the first phosystem to be discovered. The electron is excited up to the primary acceptor of PS1.  6) The primary acceptor passes the electron down another electron transport chain (ETC). NADP is turned into NADPH, which will be used for reducing power for sugar in the Calvin Cycle.

34. Non-Cyclic Electron Flow

35. Energetics of Visible Light 680 nm, PS II 700 nm, PS I

36. Light Reaction:  Movie Movie

37. Light Reaction Condensed:  Water enters Chloroplast and then Thylakoids from roots.  A photon excited an electron transport chain.  O2 is produced.  The following two products are used to produce sugars in Calvin Cycle.  ATP is produced.  NADPH is produce  Cyclic or Non-Cylic  Two photosystems named by order discovered.  Reaction centers P680 & P700 based off of what they absorb.

38. Cyclic Electron Flow:

39.  This only happens in certain conditions. Non-cyclic is the predominant one.  Uses only Photosystem 1.  Does not produce NADPH  Does not produce O2.  But does generate ATP.

41. Cyclic Electron Flow:

42. Dark Reactions (Calvin Cycle) http://www.ualr.edu/~botany/calvincycle.gif

43. Dark Reactions (Calvin Cycle):  Occur at same Time as Light Reactions  Carbon enters plant as CO2, and leaves as sugar.  Uses ATP as main energy source, and consumes NADPH to reduce (add hydrogen bonds) sugars.  If Light Energy Is not Available to Make Light Reaction Products it will stop.  Exception: some Xerophytes  Uses energy created from the Light Reaction.  Occur in the Stroma of the Chloroplasts in Leaves. http://www.ualr.edu/~botany/thylakoidmembrane.gif

44. http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-3/ch19_Dark-reactions.jpg

45. Three Phases of the Calvin Cycle:  1) Carbon Fixation  2) Reduction  3) Regeneration of CO2 Acceptor (RUBP)

46. Three Phases of the Calvin Cycle:  1) Carbon Fixation:  CO2 attaches to a 5 carbon sugar called RUBP.  Enzyme that does this is called Rubisco. Its probably the most abundant protein on earth.  So now we have a 6 carbon molecule, but its so unstable that it instantly splits in half to form two molecules of 3 phosphoglycerate.

47. Look at step one:

48. Three Phases of the Calvin Cycle:  Step 2: (Reduction)  Each 3-phosphoglycerate molecule gets:  A Phosphate from ATP  Pair of electrons from NADPH  This produces a three carbon sugar called G3P.  This process has to be done several times to get a six carbon sugar.

49. Three Phases of the Calvin Cycle:  Phase 3: Regeneration  The leftover G3P molecules are combined with more ATP to regenerate RuBP need for phase 1.  Since G3P, a three carbon molecule, is the first stable product, this method of producing glucose is called the C3 Pathway.

50. Dark Reaction (Calvin Cycle)  Movie Movie

51. C4 Photosynthesis:  C3 is not the only way to “fix” CO2.  Some plants, such as sugar cane and corn, have a more efficient way to fix CO2.  C4 pathway works well for plants found in hot, dry climates.  C3 or C4 refers to the number of carbons initially involved with making sugar.  CO2 first combines with Phosphoenolpyruvate (PEP)

52. C4 Photosynthesis:  C4 plants have two distinct types of photosynthetic cells:  Bundle Sheath  Tightly packed sheaths around the veins of a leaf.  Calvin Cycle occurs here.  Mesophyll Cells   The fixation of Carbon with PEP enzyme occurs here.  Same Fixation with Rubisco as in C 3 Plants but Occurs in the Bundle Sheath Cells, not Mesophyll Cells

53. http://www.ualr.edu/~botany/c4pathway.gif

54. CAM Photosynthesis  In these plants stoma’s are closed in the early afternoon to prevent excessive water loss during the day.  This would prevent photosynthesis in most plants.  CO2 if fixed with a different enzyme and sent to the plants vacuole.  During the day CO2 becomes unfixed and released back to start the Calvin cycle.

55. CAM Photosynthesis  Crassulacean Acid Metabolism  Another Type of PS Carried out only by Xerophytes  At Night  Stomata Are Open  Plants Fix CO 2 into a 4- Carbon Product  4-Carbon Product Stored overnight in Vacuole http://www.ualr.edu/~botany/c4andcam.jpg

56. CAM Photosynthesis  CAM Plants  Cacti, Succulents  Crops include Pineapple, Tequila Agave http://www.ualr.edu/~botany/c4andcam.jpg

58. CAM Photosynthesis  During the Day  Stomata Are Closed  CO 2 Is Released from the 4-Carbon Produce  Normal Light and Dark Reactions occur without Stomata Opening  Allows the Plants to Conserve Water during the Day  When Water Is Adequate, these Plants usually Carry out C 3 PS http://www.ualr.edu/~botany/c4andcam.jpg

59. Factors Affecting Photosynthesis  6CO 2 + 12H 2 O + Light → C 6 H 12 O 6 + 6O 2 + 6H 2 O  Availability of Water  Water (almost always) Is not a Limiting Factor for PS  So Little Is actually Used (Less than 1% of Water Absorbed) and Plants Are Made up of so much Water  Water Stress that Causes Stomata to Close can Slow or Stop PS due to Lack of CO 2 http://www.dentalindia.com/CO2b.jpg

60. Factors Affecting Photosynthesis  6CO 2 + 12H 2 O + Light → C 6 H 12 O 6 + 6O 2 + 6H 2 O  Light Quality (Color)  Chlorophyll Absorbs Light in Red (660 nm) and Blue (450 nm) Wavelengths  These Are the Photosynthetic Wavelengths of Light  Called Photosynthetically Active Radiation (PAR) http://www.firstrays.com/plants_and_light.htm

61. Factors Affecting Photosynthesis  6CO 2 + 12H 2 O + Light → C 6 H 12 O 6 + 6O 2 + 6H 2 O  Light Duration (Photoperiod)  Plants Need Sufficient Length of Light Period to Produce enough Carbs for Normal Growth  Longest Days in Northern Hemisphere Occur in June  December in Southern Hemisphere

62. Factors Affecting Photosynthesis  6CO 2 + 12H 2 O + Light → C 6 H 12 O 6 + 6O 2 + 6H 2 O  Light Intensity (Brightness)  As Light Intensity Increases, PS Rates Increase  Up to a Certain Level of Intensity  Light Saturation Point  PS Reaches Its Maximum Point  Increasing Light Intensity no Longer Increases PS Rate http://aesop.rutgers.edu/~horteng/openroof.htm

63. Factors Affecting Photosynthesis  6CO 2 + 12H 2 O + Light → C 6 H 12 O 6 + 6O 2 + 6H 2 O  Temperature  Increasing Temp will Increase Rate of PS, within Normal Ranges  Below Normal Ranges, PS Slows or Stops  Cytoplasm (Liquid inside Cells) Slows Moving  Cells may Freeze  Chilling can Change Protein and Membrane Structure  Causes Cell Content Leakage and Death http://www.semena.org/agro/diseases2/environmental-stresses-e.htm

64. Factors Affecting Photosynthesis  Leaf Age  Young, Mature Leaves Have Greatest Rate and Output of PS  Young, Immature Leaves Have High Rate of PS but Use more of what They Produce for Their Own Growth  Mature Leaves have Slower PS Rates  Defoliation of Young or Young + Mature Leaves of a Plant Drains the Plant  Must Pull from Stored Carbs in Stems and Roots to Regenerate enough Leaves to Provide needed Carbs  Reduces Root Growth  Usually Results in Y Losses in Crops

65. Plant Mitochondria and Chloroplasts May Have Evolved from Bacteria Many of the features of the mitochondrial genetic system resemble those found in prokaryotes like bacteria. This has strengthened the theory that mitochondria are the evolutionary descendants of a prokaryote that established an endosymbiotic relationship with the ancestors of eukaryotic cells early in the history of life on earth. However, many of the genes needed for mitochondrial function have since moved to the nuclear genome.