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Photosynthesis

SUN. photons. glucose. Photosynthesis. An anabolic, endergonic, carbon dioxide (CO 2 ) requiring process that uses light energy (photons) and water (H 2 O) to produce organic macromolecules (glucose). 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2.

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Photosynthesis

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  1. SUN photons glucose Photosynthesis • An anabolic, endergonic, carbon dioxide (CO2) requiring process that uses light energy (photons) and water (H2O) to produce organic macromolecules (glucose). 6CO2 + 6H2O  C6H12O6 + 6O2 • Where does photosynthesis take place?

  2. Chloroplast Mesophyll Cell Stoma Plants • Autotrophs: self-producers. • Location: 1. Leaves a. stoma b. mesophyll cells

  3. Oxygen (O2) Carbon Dioxide (CO2) Guard Cell Guard Cell Stomata (stoma) • Pores in a plant’s cuticle through which water and gases are exchanged between the plant and the atmosphere. Water (H2O)

  4. Nucleus Cell Wall Chloroplast Central Vacuole Mesophyll Cell

  5. Stroma Outer Membrane Thylakoid Granum Inner Membrane Chloroplast • Organelle where photosynthesis takes place.

  6. Thylakoid Membrane Thylakoid Space Granum Thylakoid • Why are plants green?

  7. Chlorophyll Molecules • Located in the thylakoid membranes. • Chlorophyll have Mg+in the center. • Chlorophyll pigmentsharvest energy (photons) by absorbing certain wavelengths (blue-420 nmand red-660 nmare most important). • Plants are green because the greenwavelength is reflected, not absorbed.

  8. 400 500 600 700 Short wave Long wave (more energy) (less energy) Wavelength of Light (nm)

  9. Absorption violetbluegreenyelloworangered wavelength Absorption of Chlorophyll • During the fall, what causes the leaves to change colors?

  10. Fall Colors • In addition to the chlorophyll pigments, there are other pigments present. • During the fall, the green chlorophyll pigments are greatly reducedrevealing the other pigments. • Carotenoids are pigments that are either red or yellow.

  11. Other pigments of photosynthesis include Other chlorophylls, xanthophylls, carotenoids, fucoxanthins, anthocyanins, tannins

  12. Redox Reaction • Thetransfer of one or more electronsfrom one reactantto another. • Two types: 1. Oxidation 2. Reduction

  13. Oxidation 6CO2 + 6H2O  C6H12O6 + 6O2 glucose Oxidation Reaction • The loss of electrons from a substance. • Or the gain of oxygen.

  14. Reduction 6CO2 + 6H2O  C6H12O6 + 6O2 glucose Reduction Reaction • The gain of electrons to a substance. • Or the loss of oxygen. The Source of Oxygen Produced by Photosynthesis

  15. Breakdown of Photosynthesis • Two main parts (reactions). 1. Light Reaction or Light Dependent Reaction Produces energy from solar power(photons)in the form of ATP and NADPH.

  16. Breakdown of Photosynthesis 2. Calvin Cycle or Light Independent Reaction or Carbon Fixation or C3 Fixation Uses energy(ATP and NADPH) from light rxnto make sugar (glucose).

  17. 1. Light Reaction (Electron Flow) • Occurs in the Thylakoid membranes • During the light reaction, there are two possibleroutes for electron flow. A. Cyclic Electron Flow B. Noncyclic Electron Flow

  18. P A. Cyclic Electron Flow • Occurs in the thylakoid membrane. • Uses Photosystem I only • P700 reaction center- chlorophyll a • Uses Electron Transport Chain (ETC) • Generates ATP only ADP + ATP

  19. e- Primary Electron Acceptor SUN e- ATP produced by ETC e- Photons e- P700 Accessory Pigments Photosystem I A. Cyclic Electron Flow

  20. B. Noncyclic Electron Flow • Occurs in the thylakoid membrane • Uses PS II and PS I • P680 rxn center (PSII) - chlorophyll a • P700 rxn center (PS I) - chlorophyll a • Uses Electron Transport Chain (ETC) • Generates O2, ATP and NADPH

  21. Primary Electron Acceptor 2e- Enzyme Reaction Primary Electron Acceptor 2e- 2e- ETC 2e- SUN 2e- NADPH P700 Photon ATP P680 Photon H2O 1/2O2+ 2H+ Photosystem I Photosystem II B. Noncyclic Electron Flow

  22. P (Reduced) B. Noncyclic Electron Flow • ADP + ATP • NADP+ + H NADPH • Oxygen comes from the splitting of H2O, not CO2 H2O  1/2 O2 + 2H+ (Reduced) (Oxidized)

  23. Chemiosmosis • Powers ATP synthesis. • Located in the thylakoid membranes. • UsesETCand ATP synthase(enzyme) to make ATP. • Photophosphorylation: addition of phosphate to ADP to make ATP.

  24. SUN (Proton Pumping) H+ H+ Thylakoid E T PS I PS II C high H+ concentration H+ H+ H+ H+ H+ H+ Thylakoid Space H+ ATP Synthase low H+ concentration ADP + P ATP H+ Chemiosmosis

  25. Calvin Cycle • Carbon Fixation (light independent rxn). • C3 plants(80% of plants on earth). • Occurs in the stroma. • Uses ATP and NADPH from light rxn. • Uses CO2. • To produce glucose: it takes6 turnsand uses 18 ATP and 12 NADPH.

  26. Stroma Outer Membrane Thylakoid Granum Inner Membrane Chloroplast

  27. (36C) (6C) 6C-C-C-C-C-C (unstable) 6CO2 6C-C-C 6C-C-C 12PGA (36C) 6ATP 6ATP (30C) 6C-C-C-C-C 6NADPH 6NADPH RuBP (36C) 6C-C-C 6C-C-C 6ATP 12G3P (30C) (6C) C3 C-C-C-C-C-C Glucose glucose Calvin Cycle (C3 fixation)

  28. C3 Glucose Calvin Cycle • Remember:C3 = Calvin Cycle Tracing the Pathway of CO2

  29. Photorespiration/Calvin-Benson Cycle • Occurs on hot, dry, bright days. • Stomates close. • Fixation of O2 instead of CO2. • Produces 2-C molecules instead of 3-C sugar molecules. • Produces no sugar molecules or noATP.

  30. Photorespiration • Because of photorespiration: Plants have special adaptations to limit the effect of photorespiration. 1. C4 plants 2. CAM plants

  31. C4 Plants • Hot, moist environments. • 15% of plants (grasses, corn, sugarcane). • Divides photosynthesis spatially. • Light rxn - mesophyll cells. • Calvin cycle - bundle sheath cells.

  32. C4 Pathway PEP (phosphoenolpyruvate) + CO24C (oxaloacetic acid) using enzyme PEP carboxylase PEP carboxylase has a higher affinity for CO2 than RuBP carboxylase Ocaloacetic acid + NADPH  malic acid Malic acid CO2 + pyruvic acid CO2 enters C3 pathway

  33. Malate Malate C-C-C-C C-C-C-C Transported CO2 CO2 C3 Vascular Tissue glucose C-C-C ATP PEP C-C-C Pyruvic Acid Mesophyll Cell Bundle Sheath Cell C4 Plants

  34. CAM Plants • Hot, dry environments. • 5% of plants (cactus and ice plants). • Stomates closed during day. • Stomates open during the night. • Light rxn - occurs during the day. • Calvin Cycle - occurs when CO2 is present.

  35. CAM Pathway • CO2 is captured at night and stored in vacuoles of mesophyll cells is then • CO2 is thenconverted to crassulacean acid • IN the morning, crassulacean acid is converted back to CO2 and can enter the C3 pathway • Stomata close during the day • Found in cacti & succulents

  36. Night (Stomates Open) Day (Stomates Closed) Vacuole C-C-C-C C-C-C-C C-C-C-C CO2 Malate Malate Malate CO2 C3 C-C-C ATP C-C-C glucose PEP Pyruvic acid CAM Plants

  37. Question: • Why would CAM plants close their stomates during the day? • Okay, let’s try this one more time…

  38. Calvin Cycle/ C3 Pathway C4 Pathway CAM (Crassulacean Acid Metabolism) RibuloseRuBP CO2+PEPoxaloacetic acid (4C) Enzyme=PEP carboxylase Occurs in mesophyll CO2 crassulacean acid CO2 stored in vacuoles of mesophyll cells Oxaloacetid acid + NADPHP Malic acid CO2 + pyruvic acid Occurs in bundle sheath cells crassulacean acidCO2 CO2 + RuBPDPGA (3C) Enzyme=RuBP carboxylase CO2 + RuBPDPGA (3C) Enzyme=RuBP carboxylase CO2 + RuBPDPGA (3C) Enzyme=RuBP carboxylase DPGA + 2NADPH2PGAL DPGA + 2NADPH2PGAL DPGA + 2NADPH2PGAL Stomata opened Stomata close partially to reduce H2O loss Stomata close during the day Rice, wheat, soybeans, cotton, tomatoes, Crabgrass, sugarcane corn, pineapple Cacti & succulents

  39. Resources • Photosynthesis Tutorial • Plant Metabolism • Photosynthesis Problem Set • DNA Tube • How Do Proteins Help Chlorophyll Carry Out Photosynthesis? Virtual Lab • Calvin Cycle Tutorial • Photosynthesis Animation • Transpiration Virtual Plant Lab

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