1 / 31

Chapter 7: Photosynthesis (Outline)

Chapter 7: Photosynthesis (Outline). Photosynthetic Organisms Flowering Plants as Photosynthesizers Photosynthesis Light Reactions Noncyclic Pathway Calvin Cycle Reactions Carbon Dioxide Fixation Reduction of Carbon Dioxide Regeneration of RuBP C4 CAM. Photosynthetic Organisms.

kiele
Download Presentation

Chapter 7: Photosynthesis (Outline)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 7: Photosynthesis (Outline) • Photosynthetic Organisms • Flowering Plants as Photosynthesizers • Photosynthesis • Light Reactions • Noncyclic Pathway • Calvin Cycle Reactions • Carbon Dioxide Fixation • Reduction of Carbon Dioxide • Regeneration of RuBP • C4 • CAM

  2. Photosynthetic Organisms • Organisms cannot live without energy • Almost all the energy that organisms used comes from the solar energy • Photosynthesis: • A process that captures solar energy and transforms it into chemical energy (carbohydrate) • Occurrs in higher plants, algae, mosses, photosynthetic protists and some bacteria (cyanobacteria)

  3. Photosynthetic Organisms • Autotrophs – organisms having the ability to synthesize carbohydrates • Heterotrophs – are consumers that use carbohydrates produced by photosynthesis

  4. Flowering Plants & Photosynthesis • Photosynthesis takes place in the green portions of plants • Leaf of flowering plant contains mesophyll tissue with chloroplasts • Specialized to carry on photosynthesis • CO2 enters leaf through stomata • Diffuses into chloroplasts in mesophyll cells • In the stroma, CO2 is combined with H2O to form C6H12O6 (sugar) • Chlorophyll is capable of absorbing solar energy, which drives photosynthesis

  5. Photosynthesis • The process of photosynthesis is an example of a redox reaction (i.e. movement of electrons from one molecule to another) • In living things, electrons are accompanied by hydrogen ions (H+ + e) • Oxidation is the loss of hydrogen atoms; Reduction is the gain of hydrogen atoms

  6. Photosynthesis • Carbon dioxide reduction requires energy and hydrogen atoms • Solar energy will be used to generate ATP needed to reduce CO2 to sugar • Electrons needed to reduce CO2 will be carried by a coenzyme (NADP+) • NADP+ is the active redox coenzyme of photosynthesis • When NADP+ is reduced, it accepts 2 e- and H+ • When NADP+ is oxidized, it gives up its electrons

  7. Photosynthetic Reactions • In the 1930’s, C. B. van Niel studying photosynthesis in bacteria discovered that CO2 was not split in the process of carbohydrate synthesis • Researchers later confirmed using the isotope oxygen (18O) that O2 given off from photosynthesis comes from waternot CO2 • When water splits, O2 is released and the hydrogen atoms (2 e- + H+) are taken up by NADPH

  8. Photosynthetic Reactions • Light Reactions: • Chlorophyll present in thylakoid membranes absorbs solar energy • This energizes electrons • Electrons move down electron transport chain • Pumps H+ into thylakoids • Used to makeATP out of ADP and NADPH out of NADP+ • Calvin Cycle Reactions: • In the stroma, CO2 is reduced to a carbohydrate • Reduction requires the ATP and NADPH produced in the light reactions

  9. Photosynthesis Overview

  10. Photosynthetic Pigments • Pigments: • Molecules that absorb some colors in rainbow (visible light) more than others, why? • Colors least absorbed reflected/transmitted most • Absorption Spectra • Graph showing relative absorption of the various colors of the rainbow • Chlorophylls a and b(main pigments) are green because they absorb much of the reds and blues of white light • Carotenoids are accessory pigments

  11. Phosynthetic Pigments and Photosynthesis

  12. Spectrophotometer • An instrument which measures the amount of light of a specified wavelength which passes through a medium • Amount of light absorbed at each wavelength is plotted on a graph, resulting in an absorption spectra

  13. Light Reactions • Thelight reactions utilize two photosystems: • Photosystem I (PSI) • Photosystem II (PSII) • A photosystem consists of • Pigment complex (molecules of chlorophylls a & b the carotenoids) and electron acceptor molecules thathelp collect solar energy like an antenna • Occur in the thylakoid membranes

  14. The Noncyclic Electron Pathway • Uses two photosystems, PS IandPS II • Energy enters the system when PS II becomes excited by light • Causes an electron to be ejected from the reaction center (chlorophyll a) • Electron travels down electron transport chain to PS I • PS II takes replacement electron from H2O, which splits, releasing O2 and H+ ions • The H+ ions concentrate in thylakoid chambers • Which causes ATP production, how?

  15. The Noncyclic Electron Pathway • PS I captures light energy and ejects the energized electron (e-) from the reaction center • Transferred permanently by electron acceptors to a molecule of NADP+ • Causes NADPH production NADP+ + 2 e- + H+ • NADPH and ATP produced are used by the Calvin cycle reaction (reduction of CO2) in the stroma

  16. Organization of theThylakoid Membrane • PS II: • Pigment complex and electron-acceptors • Adjacent to an enzyme that oxidizes water • Oxygen is released as a gas (by-product) • Electron transport chain: • Consists of Pq (plastoquinone) and cytochrome complexes • Carries electrons from PS II to PS I • Pumps H+ from the stroma into thylakoid space • PS I: • Pigment complex and electron acceptors • Adjacent to enzyme that reduces NADP+ to NADPH • ATP synthase complex: • Has a channel for H+ flow • Which drives ATP synthase to join ADP and Pi

  17. Organization of a Thylakoid

  18. ATP Production • Thylakoid space acts as a reservoir for H+ ions • Each time water is oxidized, two H+ remain in the thylakoid space • Electrons yield energy • Used to pump H+ across thylakoid membrane • Move from stroma into the thylakoid space • Flow of H+ back across thylakoid membrane • Energizes ATP synthase • Enzymatically produces ATP from ADP + Pi • This method of producing ATP is called chemiosmosis

  19. Calvin Cycle Reactions:Overview of C3 Photosynthesis • A cyclical series of reactions • Utilizes atmospheric carbon dioxide to produce carbohydrates • Known as C3 photosynthesis • Involves three phases: • Carbon dioxide fixation • Carbon dioxide reduction • RuBP Regeneration

  20. Calvin Cycle Reactions:Phase 1: Carbon Dioxide Fixation • CO2 enters the stroma of the chloroplast via the stomata of the leaves • CO2 is attached to 5-carbon RuBP molecule • Result in an intermediate 6-carbon molecule • This splits into two 3-carbon molecules (3PG) • Reaction is accelerated by RuBP Carboxylase (Rubisco) • CO2 now “fixed” because it is part of a carbohydrate

  21. Calvin Cycle Reactions:Phase 2: Carbon Dioxide Reduction • ATP phosphorylates each 3PG molecule and creates 1,3-bisphosphoglycerate (BPG) • BPG is then reduced by NADPH to glyceraldehyde-3-phosphate (G3P) • NADPH and some ATP used for the reduction reactions are produced in light reactions

  22. Calvin Cycle Reactions:Phase 3: Regeneration of RuBP • RuBP used in CO2 fixation must be replaced • Every three turns of Calvin Cycle, • FiveG3P molecules are used • To remakethreeRuBP molecules • 5 X 3 (carbons in G3P) = 3 X 5 (carbons in RuBP)

  23. The Calvin Cycle

  24. CO2 + RUBP Rubisco 2 3PG C3 Plants • C3 plants include more than 95% percent of the plant species on earth (e.g. trees) • Called C3 because the CO2 is first incorporated into a 3-carbon compound • In hot dry conditions, the photosynthetic efficiency of C3 plants suffers because of photorespiration • Stomata must close to avoid wilting • CO2 decreases and O2 increases • O2 starts combining with RuBP instead of CO2

  25. C4 Photosynthesis: C4 Plants • Use a supplementary method of CO2 uptake forming a 4-carbon molecule instead of the two 3-carbon molecules • In C4 plants • CO2 is inserted into a 3-carbon molecule called phosphoenolpyruvate (PEP) forming • Oxaloacetate, a C4 molecule in the mesophyll cells • Oxaloacetate is converted into malate, which is transported into the bundle sheath cells • Here the 4-carbon molecule is broken down into CO2, which enters the Calvin cycle to form sugars & starch

  26. Chloroplast distribution inC4 vs. C3 Plants

  27. CO2 Fixation in C4 vs. C3 Plants • In hot and dry climates • C4 plants avoid photorespiration as PEP in mesophyll cells does not bind to O2 • Net productivity of C4 is about 2-3 times of C3 plants • In cool, moist conditions, CO2 fixation in C3 is three times more efficient than in C4

  28. CAM Photosynthesis • Called CAM after the plant family in which it was first found (Crassulaceae) • CAM plants partition carbon fixation by time • Crassulacean-Acid Metabolism • During the night through their open stomata • CAM plants use PEPCase to fix CO2 • Forms C4 molecules (malate) • Stored in large vacuoles in mesophyll cells • During daylight • NADPH and ATP are available • Stomata closed for water conservation • C4 molecules release CO2 to Calvin (C3) cycle

  29. CO2 Fixation in a CAM Plant • Adaptive Value: Better water use efficiency than C3 plants under arid conditions due to opening stomata at night when transpiration rates are lower (no sunlight, lower temperatures, lower wind speeds, etc.)

More Related