O2 Stroma Photosystem Thylakoid NADP+ ADP + Pi CO2 Sunlight

Home , Plastocyanin

Cuticle Epidermis

Mesophyll

Vascular bundle Stoma

Vacuole Cell wall

1.58 µm

Inner membrane Chloroplast Outer membrane

Courtesy Dr. Kenneth Miller, Brown University 1

Sunlight

Photosystem

H2O O2 Thylakoid

Light-Dependent Reactions

ADP + P NADP+ NADPH i ATP

CO Organic 2 Calvin Cycle molecules

Stroma

UV Gamma rays X-rays light Infrared Radio waves

Visible light

400 nm 430 nm 500 nm 560 nm 600 nm 650 nm 740 nm

high carotenoids chlorophyll a chlorophyll b Light Light Absorbtion Absorbtion

low

400 450 500 550 600 650 700 Wavelength (nm)

Chlorophyll a: R = CH R 3 H2C CH H Chlorophyll b: R = CHO H C CH CH 3 2 3 Porphyrin N N head H Mg H N N H3C CH3 H H H O CH CO CH 2 2 3 CH 2 O C O CH 2 CH CCH 3 CH 2 CH 2 CH 2 CHCH 3 Hydrocarbon CH 2 tail CH 2 CH 2 CHCH 3 CH 2 CH 2 CH 2 CHCH 3 CH3 5

Oak leaf in summer

Oak leaf in autumn © Eric Soder 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photosystem Electron Photon acceptor e– Electron donor e– Reaction center chlorophyll Chlorophyll molecule

Thylakoid membrane

e–

e– e–

e–

Chlorophyll Chlorophyll reduced oxidized Donor Acceptor oxidized reduced

+ – + –

e– – e– e

e–

8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Excited reaction center 2. The electrons pass through the b6-f Ferredoxin complex, which uses the energy 2 released to pump protons across e– the thylakoid membrane. The proton Fd Excited reaction center gradient is used to produce ATP by chemiosmosis. NADP 2 Plastoquinone reductase e– + + NADPH – NADP + H PQ 2 e b -f 6 Plastocyanin complex Reaction center e– PC Photon 2 H+

Reaction Proton gradient formed 3. A pair of chlorophylls in the reaction Energy of electrons Energyof center for ATP synthesis center absorb two photons. This Photon excites two electrons that are passed to H O + 2 2 NADP , reducing it to NADPH. Electron e– transport from photosystem II replaces + 1 2H + /2O2 these electrons. Photosystem I

Photosystem II 1. A pair of chlorophylls in the reaction center absorb two photons of light. This excites two electrons that are transferred to plastoquinone (PQ). Loss of electrons from the reaction center produces an oxidation potential capable of oxidizing water.

Photon Light-Dependent Photon Reactions H+ ATP NADP NADPH ADP + Pi ATP ADP NADPH Antenna Calvin H+ + NADP+ Cycle Thylakoid complex membrane Fd 2e–

PQ 2e– 2e– Stroma 2e– PC H O + 2 H Proton H+ Plastoquinone Plastocyanin Ferredoxin gradient H+ Water-splitting enzyme H+

1 + Thylakoid /2O2 2H space NADP ATP Photosystem II b6-f complex Photosystem I reductase synthase

3. Photosystem I absorbs 1. Photosystem II 2. The b6-f complex 4. ATP synthase uses absorbs photons, receives electrons photons, exciting the proton gradient exciting electrons from PQ and passes electrons that are to synthesize ATP that are passed to them to plastocyanin passed through a from ADP and Pi plastoquinone (PQ). (PC). This provides carrier to reduce enzyme acts as a NADP+ to NADPH. Electrons lost from energy for the b6-f channel for protons photosystem II are complex to pump These electrons are to diffuse back into replaced by the protons into the replaced by electron the stroma using this oxidation of water, thylakoid. transport from energy to drive the photosystem II. producing O2 synthesis of ATP.

Stroma of chloroplast Light-Dependent 6 molecules of Reactions Carbon ADP+ P NADP+ NADPH i ATP dioxide (CO ) 2

Calvin Cycle

Rubisco 12 molecules of 6 molecules of 3-phosphoglycerate (3C) (PGA) Ribulose 1,5-bisphosphate (5C) (RuBP) 12 ATP

12 ADP 6 ADP 12 molecules of Calvin Cycle 1,3-bisphosphoglycerate (3C) 6 ATP 12 NADPH 4 P i 12 NADP+ 10 molecules of P 12 i Glyceraldehyde 3-phosphate (3C) 12 molecules of Glyceraldehyde 3-phosphate (3C) (G3P)

2 molecules of Glyceraldehyde 3-phosphate (3C) (G3P)

Glucose and other sugars 11

Sunlight Heat

O Electron Photo- Photo- 2 ATP system system Transport II I System H2O ADP + P i

ADP + P NADP NADPH NAD+ NADH i ATP i

Calvin Cycle

CO2 Krebs Cycle ATP

ADP + P Glucose Pyruvate i

ATP 12 13

H O H O 2 2 O2 O2

CO CO Stomata 2 2 Under hot, arid conditions, leaves lose water by The stomata close to conserve water but as a evaporation through openings in the leaves result, O2 builds up inside the leaves, and CO2 called stomata. cannot enter the leaves.

Mesophyll cell Bundle-sheath cell CO 2 Mesophyll cell

RuBP Calvin Cycle

3PG (C3) G3P

Stoma Vein a. C4 pathway Bundle- CO Mesophyll cell 2 sheath cell Mesophyll cell C 4

Bundle- CO 2 sheath cell Calvin Cycle

G3 Stoma Vein b. C4 pathway a: © John Shaw/Photo Researchers, Inc. b: © Joseph Nettis/National Audubon Society Collection/Photo Researchers, Inc. 15

CO 2

Mesophyll cell

Phosphoenolpyruvate Oxaloacetate (PEP)

AMP +

PPi

ATP + P i

Pyruvate Malate

Bundle-sheath CO2 cell

Calvin Cycle

day CO2

Calvin Cycle

G3P