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: In what types of organisms does photosynthesis take place?In what types of organisms does photosynthesis take place?

In plants, bacteria, and protists

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

Stomata Pores watergasesPores 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 )

Stomata Regulate Gas Exchange

Leaf Anatomy

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

Chloroplasts –Contain thylakoids and grana Chloroplast Mesophyll 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid space Thylakoid Granum Stroma 1 µm

Thylakoids Thylakoid Membrane Thylakoid Space Granum

Mesophyll Cell Cell Wall Nucleus Chloroplast Central Vacuole

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 absorbing wavelengthsblue-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.

Why leaves are green: interaction of light with chloroplasts

Location and Structure of Chlorophyll Molecules in Plants

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

The Electromagnetic Spectrum

Absorption of Chlorophyll wavelength Absorption violet blue green yellow orange red

Evidence that chloroplast pigments participate in photosynthesis: absorption and action spectra for photosynthesis in an alga

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 chlorophyllgreatly reduced pigmentsDuring the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments. Carotenoids redyellowCarotenoids are pigments that are either red or yellow.

Redox Reaction transferonemore electronsone reactant anotherThe 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

Oxidation (releases energy) Combining with Oxygen Combining with Oxygen Loss of ElectronsLoss of Electrons Loss of HydrogenLoss of Hydrogen Reduction (absorbs energy) Separation from OxygenSeparation from Oxygen Gain of ElectronsGain of Electrons Gain of HydrogenGain of Hydrogen

Remember: “Leo says Ger” Loss of electrons is oxidation; Gain of electrons is reduction. or “Oil Rig” Oxidation is loss; Reduction is gain.

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).

An Overview of Photosynthesis: Cooperation of the Light Reactions and the Calvin Cycle

1. Light Reaction (Electron Flow) thylakoid membranesOccurs in the thylakoid membranes light reaction two possible electron 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

How a Photosystem Harvests Light

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

Cyclic Electron Flow

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

Produces NADPH, ATP, and oxygen Figure Photosystem II (PS II) Photosystem-I (PS I) ATP NADPH NADP + ADP CALVIN CYCLE CO 2 H2OH2O O2O2 [CH 2 O] (sugar) LIGHT REACTIONS Light Primary acceptor Pq Cytochrome complex PC e P680 e–e– e–e– O2O2 + H2OH2O 2 H + Light ATP Primary acceptor Fd e e–e– NADP + reductase Electron Transport chain Electron transport chain P700 Light NADPH NADP H + + H

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)

How Noncyclic Electron Flow During the Light Reactions Generates ATP and NADPH

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

Chloroplast Granum Thylakoid Stroma Outer Membrane Inner Membrane

Chemiosmosis

The light reactions and chemiosmosis: the organization of the thylakoid membrane

Comparison of chemiosmosis in mitochondria and chloroplasts

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 and also uses CO 2 from air. To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

The Calvin Cycle

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

A Review of Photosynthesis

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

Photorespiration Because of photorespiration Plantsspecial 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

C 4 leaf anatomy and the C 4 pathway

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 (Stomata Open)Day (Stomata 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

C 4 and CAM Photosynthesis Compared

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