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Photosynthesis CR Ch 10
- 1. Photosynthesis Campbell & Reece Ch 10 Jeff Jewett American College of Sofia January 2010 Version 1.0 Image Credit: Jeff Jewett
- 2. Introduction Autotrophs – create own food, harvest energy from non-living parts of environment (also called “producers”) Plants are Photoautotrophs (as opposed to chemoautotrophs…much less common) Heterotrophs eat other organisms, or remains of other organisms (also called “consumers”) All animals are heterotrophs Image Credit: Jeff Jewett
- 3. Slide used with permission from Stephen Taylor, Bandung International School
- 4. Photosynthesis as ReDox Respiration – sugar oxidized to CO 2 , releasing energy (exergonic). O 2 accepts e - , forming H 2 0. Mitochondria use energy to create ATP. Photosynthesis – CO 2 reduced to sugar (endergonic), powered by light. H 2 0 splits, releasing O 2 .
- 5. Structure of a Chloroplast Function of photosynthesis CR Figure 10.3
- 6. Overview 1. Light-dependent (“Light”) reactions light energy is captured and stored as chemical energy (ATP, NADPH) Occurs across Thylakoid Membrane of chloroplast 2. Calvin Cycle (Light-Independent /“Dark” reactions) chemical energy (ATP, NADPH) used to make “food,” such as more complex compounds like glucose and starch Occurs in stroma of chloroplast www.wildlifecontrolsupplies.com Image Credit: 1800sunstar.com Image Credit: beaut.ie Image Credit: www.cavannapasta.com
- 8. Slide used with permission from Stephen Taylor, Bandung International School
- 9. Slide used with permission from Stephen Taylor, Bandung International School Substances that absorb visible light are pigments
- 10. Slide used with permission from Stephen Taylor, Bandung International School
- 11. Photons are only absorbed when their energy is exactly equal to difference between ground state and excited state of pigment This is why pigments only absorb some wavelengths, and have a distinct color CR Figure 10.9
- 12. CR Figure 10.11
- 13. Light Dependent Reactions capture light energy, use it to power endergonic chemical reactions (thus storing it as chemical energy), ATP and NADPH are created Water is split (using light energy), releasing e - and H + . Light is used to reduce NADP+ NADPH ADP ATP through photophosphorylation Takes place across the thylakoid membrane of chlorplast Light reactions do not produce sugar!
- 14. Light Dependent Reactions – in Thylakoid Photosystems are light harvesting complexes (light antenna) surrounding a reaction center Image Credit: Wikipedia CR Figure 10.12
- 15. CR Figure 10.14
- 16. CR Figure 10.13 Use solar energy (light) to phosphorylate ADP ATP and reduce NADP + NADPH
- 17. CR Figure 10.17
- 18. Animations Light Reactions (St. Olaf College) Light Reactions (Vermont Forestry) Light Reactions (Smith College) Calvin Cycle (Smith College) Calvin Cycle (McGraw Hill) Photosynthesis (MasteringBio…slow to buffer) Music Video – Light Reactions. Somewhat cheesy, but an excellent summary. Music Video – Calvin Cycle. Also cheesy. (starts at 1:30 in)
- 19. Compare Chemiosmosis CR Fig 10.16 page 198
- 20. ATP and NADPH produced, oxygen is waste, water consumed, ATP produced; NAD+, FAD, and water as waste; Oxygen consumed In/Out Protons flow OUT through ATP Synthase (to stroma), producing ATP (ADP + Phosphate ATP) Protons flow IN through ATP Synthase (to mito. Matrix) , producing ATP (ADP + Phosphate ATP) ATP Production Water is split (photolysis), giving electrons to ETC. Water is oxidized. This is the Oxygen-producing step! Water is produced , by reducing Oxygen and using electrons from ETC This is the Oxygen-requiring step! Water Pump protons (H + ) INTO inner thylakoid space from stroma Pump protons (H + ) OUT of matrix to intermembrane space Proton pumps in ETC Reduced , RECEIVING high-energy electrons from the ETC NAD P + + 2e- (from ETC) NAD P H Oxidized , GIVING high-energy electrons to the ETC NADH NAD + + 2e- (to ETC) Action of electron carrier innermost membrane (of 3), called thylakoid membrane inner membrane (of 2), folds called “cristae” Location Electron Carriers: NAD P + NAD P H Electron Carriers: NADH NAD + , FADH 2 FAD Electron Carriers ETC in Chloroplasts (Light Reactions of Photosynthesis ) ETC in Mitochondria – Aerobic Cellular Respiration COMPARISON OF ETC. in Respiration and Photosynthesis
- 21. Calvin Cycle – “Pour some sugar on me…” Why bother? Uses ATP and NADPH from the light-dependent reactions to convert CO 2 into sugar (glucose, C 6 H 12 O 6 ) Reduction of CO 2 is endergonic process, powered by ATP and NADPH 3 phases Fixation of CO 2 Reduction of CO 2 Regeneration of RuBP
- 22. Calvin Cycle Phase 1: Carbon Fixation Take CO 2 from air (inorganic) organic molecules 1 C attaches to 5C Ribulose BisPhosphate (RuBP) Catalyzed by RuBisCo! Unstable 6C intermediate, splits into 2 phosphoglycerates (3C each)
- 23. Calvin Cycle Phase 2: Reduction / Energy Input Reduce Use 12 NADPH Phosphorylate! Use 12 ATP Create 12 G3P (from 6 CO 2 ) Use 2 G3P to make glucose, cellulose, everything else!
- 24. Calvin Cycle Phase 3: Regenerate RuBP Out of 12 G3P : 2 G3P glucose 10 G3P regenerate RuBP Use 6 more ATP Reactions are complex
- 25. You’ve seen G-3-P before… Glycolysis! (CR Figure 9.9 page 168)
- 26. Calvin & Krebs Compared Ribulose BisPhosphate Oxaloacetate Cycle Regenerates Hans Melvin First Name NAD + NADH (Reduced) ADP + P i ATP NADPH NADP + (Oxidized) ATP ADP + Pi Action of Energy Carriers Oxidation Reduction What happens to Carbon Compound? CO 2 G3P (3C) Two used to make C 6 H 12 O 6 Final C Compound Pyruvate (3C) CO 2 Entry C compound Krebs Cycle (Respiration) Calvin Cycle (Photosynthesis)
- 27. Links Why Study Photosynthesis? Top 10 Reasons to love RuBisCo Biographies of Important People in Photosynthesis (many won Nobel Prizes)
- 28. Image source unknown. Question from the IBO . Slide adapted with permission from Stephen Taylor, Bandung International School Quiz Slide
Editor's Notes
- #4: Photosynthesis title, definition and equation.
- #9: Chloroplast: colour TEM, parts and functions.
- #10: Why does a leaf look green?
- #11: Action spectrum of photosynthesis shows wavelengths used for light dependent reactions. Different colours are different wavlengths. The green region is not used, so green light is reflected and seen.
- #13: Outside of chloroplasts, chlorophyll will flouresce (release light) and emit heat when you shine light on it
- #17: Energized Electrons transferred from reaction center (P680) to “primary acceptor” (the start of the Electron Transport Chain) 2 Water molecules are split into 4H+, 4e-, and O2. (yay, breathing!). H+ start proton gradient. Electrons reduce P680 (strongest oxidizing agent in nature…those electrons MUST be replaced). H+ pumped to build up gradient. Electrons passed down ETC from Photosystem II to Photosystem I. Loss of energy in e- on ETC provides power to pump protons into thylakoid space (just like respiration, but opposite direction!!!), creating a proton gradient across the thylakoid membrane. Protons flow across thylakoid through ATP Synthase, creating ATP (chemiosmosis, again!) Light also harvested at P1 (P700), excited electrons given to another ETC (no protons pumped), eventually used to reduce NADP+ to NADPH . Electrons ETC fill the electron hole at P700, making everybody happy.
- #18: From Biologycorner.com Photosystems I & II Photosystem II - photons split water molecules (producing O2), electrons produced from the split travel down electron transport chain. Energy provided in the transport chain is used to make ATP from ADP Photosystem I - photons boost electrons to a higher energy state, electrons travel down electron transport chain, energy is used to make NADPH from NADP. The ATP and the NADPH are used for the next main step, the Calvin cycle,or "Light independent reactions" - also called the Dark Reaction
- #29: Chloroplast: structure’s relationship with function