Capturing Solar Energy The Light-Dependent Reactions Chapter 4.1 & 4.2 McGraw-Hill Ryerson Biology 12 (2011)

Water-splitting Z-protein splits H2O into: Where do each of these go? 2 protons (H+) 2 electrons (e-) ½O2. Where do each of these go? Oxygen _______________ Protons _______________ Electrons ______________ ???

Water-splitting 1 electron goes to PSII Enters ground state In your textbook it does say 2, but that’s because the whole electron flow occurs twice

Photoexcitation Chlorophyll Molecules Ground State Excitation & Fluorescence Reaction center (chlorophyll a) P700 in PSI, P680 in PSII Primary Electron Acceptor

Refer to page 156-157 of your textbook

Noncyclic Electron Flow Primary electron acceptor (pheophytin) Redox reactions Electron carrier Plastiquinone takes excited electron

Noncyclic Electron Flow Q cycle Plastiquinone along with a protein b6-f cytochrome complex Pumps 4 protons per 2 electrons B6-f complex with plastoquinone create a complicated mechanism to introduce 4 protons into the lumen (you’ll learn this in university!)

Noncyclic Electron Flow Q cycle Plastocyanin takes excited electron Transfer electron to PSI (back in ground state)

Noncyclic Electron Flow Primary electron acceptor (pheophytin) Redox reactions Electron carrier ferredoxin takes excited electron

Noncyclic Electron Flow NADPH production Protein NADP Reductase uses 2 electrons to reduce NADP+ + H+  NADPH

Noncyclic Electron Flow ATP production Protons accumulate to create gradient ATPase complex pumps proton out Movement allows ADP + Pi  ATP

Noncyclic Electron Flow NADPH production Protein NADP Reductase uses 2 electrons to reduce NADP+ + H+  NADPH ATP production Protons accumulate to create gradient ATPase complex pumps proton out Movement allows ADP + Pi  ATP The products formed, ATP and NADPH proceed to the Calvin Cycle To review the entire process, review pg 158-159 of your textbook

Noncyclic Electron Flow

Cyclic Electron Flow Some cases where PSI does it’s own thing

Cyclic Electron Flow Some cases where PSI does it’s own thing

Cyclic Electron Flow Why do you think this would happen? What are its advantages and its disadvantages?

C3 vs C4 photosynthesis C3 photosynthesis Photorespiration AKA: Calvin Cycle Most plants go through this form Optimal temperature: (15oC – 25oC) Photorespiration O2 bonds to Rubisco instead of CO2 Rubisco + O2  PGA (3 Cs) + glycolate (2 Cs) 2 glycolate  CO2 + G3P (returned to Calvin Cycle) C3 plants continually do this and lose 20-50% of carbon

C3 vs C4 photosynthesis C4 photosynthesis AKA: “Hatch-slack pathway” A CO2 delivery system, More CO2 to outcompete O2 for rubisco in interior cells Oxaloacetate and malate are the CO2 transporters

The upper half is the C4 photosynthesis Please refer to Pg 168-170 of your textbook The lower half is the Calvin Cycle

C3 vs C4 vs CAM photosynthesis C3 Photosynthesis C4 Photosynthesis Optimal Temperature 15oC-25oC Energy Cost Uses up 18 ATP Examples of plants Soybeans, Kentucky bluegrass, sunflowers, etc. 30oC-47oC Uses up 30 ATP Tropical plants; Sugar cane, maize, corn

CAM Plants CAM – Crassulacean Acid Metabolism Stomata open at night to take in CO2 CO2 incorporated into C4 organic acids Organic acids stored in vacuoles until morning Organic acids release CO2 to enter Calvin Cycle Please refer to pg 170-171 of your textbook

C4 vs CAM Plants C4 plants have carbon fixation and Calvin cycle in different compartments Carbon fixation in mesophyll cells Calvin cycle in bundle-sheath cell CAM plants have processes occur in same compartment but different times Carbon fixation into organic acids at night Calvin Cycle during the day

Homework 4.1 Pg. 165 # 1 – 8, 11, 12 4.2 Pg. 171 #1, 3 - 13