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Photosynthesis 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?


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

Stomata (stoma):

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

Mesophyll Cell:

Mesophyll Cell Cell Wall Nucleus Chloroplast Central Vacuole


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


Thylakoid Thylakoid Membrane Thylakoid Space Granum


Question: Why are plants green?

Chlorophyll Molecules:

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 .

Wavelength of Light (nm):

Wavelength of Light (nm) 400 500 600 700 Short wave Long wave (more energy) (less energy)

Absorption of Chlorophyll:

Absorption of Chlorophyll wavelength Absorption violet blue green yellow orange red


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

Fall 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:

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

Oxidation Reaction:

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

Reduction Reaction:

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

Breakdown of Photosynthesis:

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:

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

1. Light Reaction (Electron Flow):

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:

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

A. Cyclic Electron Flow:

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

B. Noncyclic 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 O 2 , ATP and NADPH

B. Noncyclic Electron Flow:

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 + 2H + ATP NADPH Photon 2e - 2e - 2e - 2e - 2e - SUN Photon

B. Noncyclic Electron Flow:

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


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 .


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

Calvin Cycle:

Calvin Cycle 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 (C3 fixation):

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

Calvin Cycle:

Calvin Cycle Remember: C3 = Calvin Cycle C 3 Glucose


Photorespiration Occurs on hot, dry, bright days . Stomates close . Fixation of O 2 instead of CO 2 . 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:

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:

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 C 3 Malate Transported glucose Vascular Tissue

CAM Plants:

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 CO 2 is present.

CAM Plants:

CAM Plants Night (Stomates Open) Day (Stomates Closed) Vacuole C-C-C- C Malate C-C-C- C Malate Malate C-C-C- C CO 2 CO 2 C 3 C-C-C Pyruvic acid ATP C-C-C PEP glucose


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

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