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Photosynthesis: The Sun's Gift to Life

Explore the significance of photosynthesis in converting light into energy for plants, vital for sustenance of all organisms. Discover the process, chlorophyll, leaf structure, and more.

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Photosynthesis: The Sun's Gift to Life

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

  2. Life in the Sun • 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

  3. 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.

  4. 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

  5. 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

  6. The Chloroplast:

  7. Chloroplast • Organelle • Location of Photosynthesis http://www.lclark.edu/~seavey/Bio100_03/Lecture%20notes/lecture_Feb_11.html

  8. 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

  9. The Chloroplast:

  10. 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/

  11. 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

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

  13. Why Plants are Green?

  14. 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

  15. 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

  16. Photosynthetic Reactions • Overall Equation • Simplified

  17. 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

  18. 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

  19. The production of ATP by chemiosmosis in photosynthesis Thylakoidcompartment(high H+) Light Light Thylakoidmembrane Antennamolecules Stroma(low H+) ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE Figure 7.9

  20. 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

  21. Overview: • 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 O2 • The Calvin cycle assembles sugar molecules from CO2 using the high energy products of the light reactions

  22. Non-Cyclic Electron Flow

  23. Non-Cyclic Electron Flow • 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).

  24. 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.

  25. Non-Cyclic Electron Flow

  26. Non-Cyclic Electron Flow • 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.

  27. Non-Cyclic Electron Flow

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

  29. Light Reaction: • Movie

  30. 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.

  31. Cyclic Electron Flow:

  32. Cyclic Electron Flow: • 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.

  33. Cyclic Electron Flow:

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

  35. 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

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

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

  38. 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.

  39. Look at step one:

  40. 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.

  41. 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.

  42. Dark Reaction (Calvin Cycle) • Movie

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