PHOTOSYNTHESIS

Photosynthesis anabolic, endergonic, carbon dioxide (CO 2 )light energy (photons)water (H 2 O)organic macromolecules (glucose).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 glucose SUN photons

Question: Where does photosynthesis take place?Where does photosynthesis take place?

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

Stomata (stoma) Poreswater gasesPores in a plant’s cuticle through which water and gases are exchanged between the plant and the atmosphere. Guard Cell Carbon Dioxide (CO 2 ) Oxygen (O 2 )

Mesophyll Cell Cell Wall Nucleus Chloroplast Central Vacuole

Chloroplast OrganellephotosynthesisOrganelle where photosynthesis takes place. Granum Thylakoid Stroma Outer Membrane Inner Membrane

Thylakoid Thylakoid Membrane Thylakoid Space Granum

Question: Why are plants green?Why are plants green?

Chlorophyll Molecules thylakoid membranesLocated in the thylakoid membranes. Mg +Chlorophyll have Mg + in the center. Chlorophyll pigments absorbingwavelengthsblue-420 nmChlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red-660 nm are most important). Plantsgreen wavelengthreflectednot absorbedPlants are green because the green wavelength is reflected, not absorbed.

Wavelength of Light (nm) Short waveLong wave (more energy)(less energy)

Absorption of Chlorophyll wavelength Absorption violet blue green yellow orange red

Question: During the fall, what causes the leaves to change colors?During the fall, what causes the leaves to change colors?

Fall Colors pigmentsIn addition to the chlorophyll pigments, there are other pigments present. green chlorophyll greatly reduced pigmentsDuring the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments. Carotenoidsred yellowCarotenoids are pigments that are either red or yellow.

Redox Reaction transferonemore electrons one reactantanotherThe transfer of one or more electrons from one reactant to another. Two types:Two types: 1.Oxidation 2.Reduction

Oxidation Reaction losselectronsThe loss of electrons from a substance. gainoxygenOr the gain of oxygen. glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Oxidation

Reduction Reaction gainThe gain of electrons to a substance. lossoxygenOr the loss of oxygen. glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Reduction

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

Breakdown of Photosynthesis 2.Calvin Cycle or Light Independent Reaction or Carbon Fixation or C 3 Fixation energy(ATP and NADPH)light rxnsugar (glucose). Uses energy (ATP and NADPH) from light rxn to make sugar (glucose).

1. Light Reaction (Electron Flow) Thylakoid membranesOccurs in the Thylakoid membranes light reactiontwo possibleelectron flowDuring the light reaction, there are two possible routes for electron flow. A.Cyclic Electron Flow B.Noncyclic Electron Flow

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

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

B. Noncyclic Electron Flow thylakoid membraneOccurs in the thylakoid membrane PS IIPS IUses PS II and PS I P680 rxn center (PSII) - chlorophyll a P700 rxn center (PS I) - chlorophyll a Electron Transport Chain (ETC)Uses Electron Transport Chain (ETC) Generates O 2, ATP and NADPHGenerates O 2, ATP and NADPH

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

B. Noncyclic Electron Flow ATPADP +  ATP NADPHNADP + + H  NADPH Oxygen comes from the splitting of H 2 O, not CO 2Oxygen comes from the splitting of H 2 O, not CO 2 H 2 O H 2 O  1/2 O 2 + 2H + (Reduced) P (Oxidized)

Chemiosmosis ATP synthesisPowers ATP synthesis. thylakoid membranesLocated in the thylakoid membranes. (enzyme)Uses ETC and ATP synthase (enzyme) to make ATP. Photophosphorylation: phosphateADPATPPhotophosphorylation: addition of phosphate to ADP to make ATP.

Chemiosmosis

Calvin Cycle Carbon Fixation (light independent rxn).Carbon Fixation (light independent rxn). C 3 plants (80% of plants on earth). Occurs in the stroma. Uses ATP and NADPH from light rxn. Uses CO 2. To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

Chloroplast Granum Thylakoid Stroma Outer Membrane Inner Membrane

Calvin Cycle (C 3 fixation) 6CO 2 6C-C-C-C-C-C 6C-C-C 6C-C-C-C-C 12PGA RuBP 12G 3 P (unstable) 6NADPH 6ATP C-C-C-C-C-C Glucose (6C) (36C) (30C) (6C) 6C-C-C C3C3 glucose

Calvin Cycle Remember:C3 = Calvin CycleRemember: C3 = Calvin Cycle C3C3 Glucose

Photorespiration hot, dry, bright daysOccurs on hot, dry, bright days. Stomates close. Fixation of O 2 instead of CO 2. 2-C molecules3-C sugar moleculesProduces 2-C molecules instead of 3-C sugar molecules. Produces no sugar molecules or no ATP.

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

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

C4 Plants Mesophyll Cell CO 2 C-C-C PEP C-C-C-C Malate ATP Bundle Sheath Cell C-C-C Pyruvic Acid C-C-C-C CO 2 C3C3 Malate Transported glucose Vascular Tissue

CAM Plants Hot, dry environmentsHot, dry environments. 5% of plants (cactus and ice plants).5% of plants (cactus and ice plants). Stomates closed during day.Stomates closed during day. Stomates open during the nightStomates open during the night. Light rxn - occurs during the day. Calvin Cycle - occurs when CO 2 is present.

CAM Plants Night (Stomates Open)Day (Stomates Closed) Vacuole C-C-C-C Malate C-C-C-C Malate C-C-C-C CO 2 C3C3 C-C-C Pyruvic acid ATP C-C-C PEP glucose

Question: Why would CAM plants close their stomates during the day?Why would CAM plants close their stomates during the day?