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  1. 1. Photosynthesis
  2. 2. What is photosynthesis? • Photo = light • Synthesis = the making of something by combining separate components • Photosynthesis is the process of converting light energy into chemical energy that is store in carbohydrates and other organic molecules • A process that is carried out by photosynthetic autotrophs such as plants, protists (i.e. algae), and some bacteria • Occurs in the chloroplasts
  3. 3. The location and structure of chloroplasts LEAF CROSS SECTION MESOPHYLL CELL LEAF Chloroplast Mesophyll CHLOROPLAST Intermembrane space Outer membrane Inner membrane Thylakoid compartmentThylakoidStroma Granum StromaGrana
  4. 4. What are the reactants & Products? The goal is to know when and how each reactant is used during the process of photosynthesis
  5. 5. What are the two stages of photosynthesis?
  6. 6. • The Calvin cycle makes sugar from carbon dioxide – ATP generated by the light reactions provides the energy for sugar synthesis – The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose Light Chloroplast Light reactions Calvin cycle NADP+ ADP + P The light reactions convert solar energy to chemical energy • Produce ATP & NADPH AN OVERVIEW OF PHOTOSYNTHESIS
  7. 7. Structure & Function of a photosystem Components of a photosystem: •Light harvesting complex = pigment molecules attached to proteins •Reaction Center Complex = proteins that contain a special pair of chlorophyll a molecules What happens in a photosystem: 1.Chlorophyll pigment absorbs light 2.Energy transferred from pigment to pigment 3.Energy reaches reaction center where special chlorophyll a uses the energy to launch an e- to a higher energy level 4. primary e- acceptor captures e- Study this figure of How a photosystem harvests light Thylakoidmembrane Photon Photosystem STROMA Light- harvesting complexes Reaction- center complex Primary electron acceptor Transfer of energy Special pair of chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) e−
  8. 8. Photon Photon Water-splitting photosystem NADPH-producing photosystem ATP mill Two types of photosystems cooperate in the light reactions
  9. 9. Cytochrome complex Primary acceptor Primary acceptor H2O O2 2 H+ + 1 /2 P680 Light Pigment molecules Photosystem II (PS II) Photosystem I (PS I) Pq Pc ATP 1 2 3 5 6 7 8 Electron transport chain Electron transport chain P700 Light + H+ NADP+ NADPH NADP+ reductase Fd e− e− e− e− 4 e− e− • Water is split, generating molecular oxygen, stripping electrons for electron transport chain and leaving H+ to remain • The flow of electrons through photosystems during light reaction lead to the production of NADPH and ATP
  10. 10. Photosynthesis: Light Reactions and Chemiosmosis STROMA (low H+ concentration) STROMA (low H+ concentration) THYLAKOID SPACE (high H+ concentration) Light Photosystem II Cytochrome complex Photosystem I Light NADP+ reductase NADP+ + H+ To Calvin Cycle ATP synthase Thylakoid membrane 2 1 3 NADPH Fd Pc Pq 4 H+ 4 H+ +2 H+ H+ ADP + P i ATP 1 /2 H2O O2 H+ H+ H+ H+
  11. 11. 2 H+ + 1 /2 Water-splitting photosystem Reaction- center chlorophyll Light Primary electron acceptor Energy to make Electron transport chain Primary electron acceptor Primary electron acceptor NADPH-producing photosystem Light NADP+ 1 2 3 Summary: How the Light Reactions Generate ATP and NADPH
  12. 12. BIG PICTURE: •Aka Dark Reactions or Light- independent reactions •Anabolic process: making carbohydrates from smaller molecules •Carbon in the form of CO2 goes into the cycle, and comes out in the form of sugar. •ATP and NADPH from the light reactions serve as an energy sources that drives the conversion of CO2 to glucose •3-carbon sugar is produced with each turn of the cycle Calvin Cycle Question: Will the Calvin Cycle occur in the dark? WHY or WHY NOT?
  13. 13. Review: Photosynthesis uses light energy to make food molecules Light Chloroplast Photosystem II Electron transport chains Photosystem I CALVIN CYCLE Stroma Electrons LIGHT REACTIONS CALVIN CYCLE Cellular respiration Cellulose Starch Other organic compounds Connections: What is the relationship between the light reactions and the Calvin Cycle?
  14. 14. Create your own mindmap of photosynthesis