PHOTOSYNTHESIS

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 glucose SUN photons

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

In plants, bacteria, and protists

Photosynthesis Animations Comprehensive Overview: http://www.wiley.com/college/test/0471787159/biology_basics/animations/photosynthesis.html Cyclic and Noncyclic Photophosphorylation: http://highered.mcgraw-hill.com/olc/dl/120072/bio12.swf Electron Transport Chain: http://highered.mcgraw-hill.com/olc/dl/120072/bio13.swf Light Reactions: http://www.biologyalive.com/life/classes/apbiology/documents/Unit%207/10_Lectures_PPT/media/10_17LightReactions_A.swf Photophosphorylation: http://bcs.whfreeman.com/thelifewire/content/chp08/0802002.html   Proton Pumps: http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/proton_pump.html Calvin Cycle: http://www.biologyalive.com/life/classes/apbiology/documents/Unit%207/10_Lectures_PPT/media/10_18CalvinCycle_A.swf Calvin Cycle: http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter8/calvin_cycle.html

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

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

Stomata Regulate Gas Exchange 8

Leaf Anatomy 9

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

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

Thylakoids Thylakoid Membrane Granum Thylakoid Space

Mesophyll Cell Nucleus Cell Wall Chloroplast Central Vacuole

Question: Why are plants green?

Chlorophyll Molecules Located in the thylakoid membranes. Chlorophyll have Mg+ in the center. Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red-660 nm are most important). Plants 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) 400 500 600 700 Short wave Long wave (more energy) (less energy)

The Electromagnetic Spectrum

Absorption of Chlorophyll violet blue green yellow orange red Absorption wavelength

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?

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

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

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

Reduction Reaction The gain of electrons to a substance. Or the loss of oxygen. Reduction glucose 6CO2 + 6H2O  C6H12O6 + 6O2

Oxidation (releases energy) Combining with Oxygen Loss of Electrons Loss of Hydrogen Reduction (absorbs energy) Separation from Oxygen Gain of Electrons Gain 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). 1. Light Reaction or Light Dependent Reaction 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 C3 Fixation 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) Occurs in the thylakoid membranes During the light reaction, there are two possible routes for electron flow. A. Cyclic Electron Flow B. Noncyclic Electron Flow

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 P

How a Photosystem Harvests Light

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

Cyclic Electron Flow

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

Electron transport chain Figure 10.13 Photosystem II (PS II) Photosystem-I (PS I) ATP NADPH NADP+ ADP CALVIN CYCLE CO2 H2O O2 [CH2O] (sugar) LIGHT REACTIONS Light Primary acceptor Pq Cytochrome complex PC e P680 e– + 2 H+ Fd reductase Electron Transport chain Electron transport chain P700 + 2 H+ + H+ Produces NADPH, ATP, and oxygen 7 4 2 8 3 5 1 6

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

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

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

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

Chloroplast Stroma Outer Membrane Thylakoid Granum Inner Membrane

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

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). C3 plants (80% of plants on earth). Occurs in the stroma. Uses ATP and NADPH from light rxn and also uses CO2 from air. To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

The Calvin Cycle

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

Calvin Cycle Remember: C3 = Calvin Cycle C3 Glucose

A Review of Photosynthesis

Photorespiration 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 no ATP.

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

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

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

C4 leaf anatomy and the C4 pathway

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.

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

C4 and CAM Photosynthesis Compared

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

List the reactants necessary for photosynthesis to take place. In terms of light absorption and reflection explain why most plants appear to be green. Explain the role of carotenoids in plants.