Photosynthesis Converting Light Energy to Chemical Energy

Photosynthesis Is an Endergonic Reaction + glucose (C 6 H 12 O 6 ) + 6 O 2 OH O O CH 2 OH OO + 6 CO H 2 O OOC O HH Energy Supplied + energy =

Photosynthesis Occurs in Chloroplasts of Leaf Mesophyll Cells

Leaf Structure Mesophyll Cells Upper Epidermis Lower Epidermis VeinVein StomaStoma

Chloroplast Structure Inner & Outer Membranes Thylakoids (contain pigments) Granum (stack of thylakoids) Stroma (interior matrix)

Light, Chloroplast Pigments, & Photosynthesis Gamma Rays X-RaysUVInfrared Micro- waves Radio Waves Visible Light Wavelength (nanometers)

% Light Absorption Wavelength (nanometers) Visible Light Chlorophyll Carotenoids Phycocyanin Collectively

Photosynthetic Pigments ChlorophyllChlorophyll –major photosynthetic pigment –absorbs violet, blue, red wavelengths, reflects green Accessory PigmentsAccessory Pigments –Carotenoids absorb blue and green, reflect yellowabsorb blue and green, reflect yellow –Phycocyanins absorb green and yellow, reflect blueabsorb green and yellow, reflect blue

Glucose O2O2O2O2 Photosynthesis Involves Two Sets of Reactions Light-Dependent Reactions (in thylakoids) Light-Independent Reactions (in stroma) Depleted Carriers (ADP, NADP + ) Energized Carriers (ATP, NADPH) H2OH2OH2OH2O CO 2 +H 2 O

Light-Dependent Reactions Energy from light is used to formEnergy from light is used to form –ATP: energy carrier –NADPH: electron carrier Occur in photosystems located in thylakoid membranesOccur in photosystems located in thylakoid membranes –organized array of pigment molecules –each photosystem contains light-harvesting complex, with reaction centerlight-harvesting complex, with reaction center electron transport systemelectron transport system

Absorbs light energy and transfers it to Reach electron carriers Electrons absorb energy Photosystems II and I

Electron Flow in Light-dependent Reactions

Summary of Light-Dependent Reactions ReactantsProducts Water electron supplier ½ O 2 Protons (2H + ) Electrons (2e - ) ADP energy carrier + energy + PO 4  ATP NADP+ electron carrier + 2e - + H +  NADPH

Applying Your Knowledge A.Where is ATP produced? B.Which one contains an electron transport system? C.Where is NADPH produced? 1.Photosystem I 2.Photosystem II 3.Both PS I and PS II 4.Neither PS I nor PS II

Chemiosmosis Produces ATP

ATP is Produced by Chemiosmosis Diffusion of hydrogen ions (H + ) through a differentially permeable membrane, resulting in ATP productionDiffusion of hydrogen ions (H + ) through a differentially permeable membrane, resulting in ATP production –energy from electron transport pumps H + to interior of thylakoid –H + diffuses to exterior through pores of ATP-synthesizing enzyme –movement of H + provides energy for ATP synthesis

Light-Independent Reactions (C3 Photosynthesis Cycle) Produce Glucose (C 6 H 12 O 6 ) using CO 2 as a carbon sourceProduce Glucose (C 6 H 12 O 6 ) using CO 2 as a carbon source Occur in stroma of chloroplastOccur in stroma of chloroplast Use ATP and NADPH from Light- Dependent ReactionsUse ATP and NADPH from Light- Dependent Reactions Six turns of the cycle produce one glucose moleculeSix turns of the cycle produce one glucose molecule

The C 3 Cycle of Carbon Fixation 6-Carbon Compounds form briefly Cycle is named for 3-Carbon Compounds

C3 Photosynthesis Cycle CCCCCC 6-Carbon Intermediates X 6 CCCCCC 3-Carbon Intermediates X 12 CCCCCC Modified 3-Carbon Intermediates X ATP 12 NADPH C Carbon Dioxide X 6 12 ADP 12 ADP 12 NADP + Glucose 6-Carbon Product CCCCCC Rearrangements to reform 5C reactants 6 ATP 6 ADP 3-Carbon X 2 3-Carbon X 10 CCCCC 5-Carbon Reactants X 6 RUBISCO

Summary of Light-Independent Reactions ReactantsProducts 6 CO 2 Glucose (C 6 H 12 O 6 ) ATP energy carrier ADP + PO 4 + energy (in bonds of glucose) NADPH electron carrier NADP + + 2e - + H + (used in C3 reactions) OH O O CH 2 OH

A Summary of Photosynthesis Light-dependent reactions occur in thylakoids Light- independent reactions (c 3 cycle) occur in stroma

Applying Your Knowledge A.Which reactions produce glucose? B.Which reactions use water? C.Which reactions release oxygen? D.Which reactions use energy from ATP? 1.Light-Dependent Reactions 2.Light-Independent Reactions 3.Neither choice 1 nor 2 4.Both choices 1 and

Adaptations to Hot and Dry Conditions Plants close leaf pores (stoma) to avoid losing water at high temperaturesPlants close leaf pores (stoma) to avoid losing water at high temperatures Closed stoma prevent diffusion of CO 2 into leaf and diffusion of O 2 out of leafClosed stoma prevent diffusion of CO 2 into leaf and diffusion of O 2 out of leaf Excess O 2 leads to photorespiration, interferes with photosynthesisExcess O 2 leads to photorespiration, interferes with photosynthesis C4 Pathway is used to continue CO 2 collectionC4 Pathway is used to continue CO 2 collection

C 3 Plants & the C 3 Pathway C 3 plants use the C 3 pathway In a C 3 plant, most chloroplasts are in mesophyll cells.

C 3 Plants & the C 3 Pathway RUBISCO combines with O 2 instead of CO 2 Much photorespiration occurs under hot, dry conditions RUBISCO

C 4 Plants & the C 4 Pathway C 4 plants use the C 4 pathway In a C 4 plant, both mesophyll & bundle- sheath cells contain chloroplasts.

C 4 Plants & the C 4 Pathway Almost no photorespiration occurs under hot, dry conditions. CO 2 is captured with a highly specific enzyme. Much glucose synthesis occurs. Mesophyll cell in a C 4 plant Bundle-sheath cell in a C 4 plant 4C 3C RUBISCO

Interconnections: Photosynthesis & Respiration