Where does most of our society s energy come from (think of fossil fuels), how does that energy become fixed for human use?

The Photosynthesis equation 6 CO 2 + 12 H 2 O + Light energy C 6 H 12 O 6 + 6 O 2 + 6 H 2 O Simplified - 6 CO 2 + 6 H 2 O + Light energy C 6 H 12 O 6 + 6 O 2

Autotrophs sustain themselves without eating other organisms (producers of the biosphere) (a) Plants (c) Unicellular protist 10 µm (e) Purple sulfur bacteria 1.5 µm (b) Multicellular alga (d) Cyanobacteria 40 µm

light reactions (the photo part) Makes ATP Makes NADPH Calvin cycle (the synthesis part) Uses CO2 from the air and ATP and NADPH from the light reaction to make sugar Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 10-5-4 H 2 O CO 2 Light Light Reactions NADP + ADP + P ATP i Calvin Cycle NADPH Chloroplast O 2 [CH 2 O] (sugar)

Capture solar energy using pigments

A photosytem the complex shown light-harvesting complexes (pigment molecules bound to proteins) funnel the energy of photons to the reaction center Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Electrons fall down an electron transport chain Energy helps pump hydrogen ions into the thylakoids Diffusion of H + (protons) across the membrane drives ATP synthesis Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 10-13-5 2 H + + 1 / 2 O 2 3 H 2 O Primary acceptor e 2 Pq 4 Cytochrome complex Pc Primary acceptor e Fd e e 7 8 NADP + reductase NADP + + H + NADPH e e P680 5 P700 Light 1 Light 6 ATP Photosystem II (PS II) Pigment molecules Photosystem I (PS I)

Fig. 10-14 ATP e e e e e e NADPH Mill makes ATP e Photosystem II Photosystem I

Fig. 10-16 Mitochondrion Chloroplast MITOCHONDRION STRUCTURE Intermembrane space Inner membrane Electron transport chain H + Diffusion CHLOROPLAST STRUCTURE Thylakoid space Thylakoid membrane Key Matrix ATP synthase Stroma ADP + P i H + ATP Higher [H + ] Lower [H + ]

Fig. 10-17 STROMA (low H + concentration) Light Photosystem II 4 H + Cytochrome complex Light Photosystem I Fd NADP + reductase 3 NADP + + H + Pq NADPH H 2 O THYLAKOID SPACE (high H + concentration) e e 1 1 / 2 O 2 +2 H + 2 4 H + Pc To Calvin Cycle STROMA (low H + concentration) Thylakoid membrane ATP synthase ADP + P i H + ATP

The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Carbon enters the cycle as CO 2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P) For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO 2 The Calvin cycle has three phases: Carbon fixation (catalyzed by rubisco) Reduction Regeneration of the CO 2 acceptor (RuBP) Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 10-18-1 Input 3 (Entering one at a time) CO 2 Phase 1: Carbon fixation Rubisco 3 P Short-lived intermediate 3 P P 6 P Ribulose bisphosphate 3-Phosphoglycerate (RuBP) P

Fig. 10-18-2 Input 3 (Entering one at a time) CO 2 Phase 1: Carbon fixation Rubisco 3 P Short-lived intermediate 3 P P 6 P Ribulose bisphosphate 3-Phosphoglycerate (RuBP) P 6 6 ADP ATP Calvin Cycle 6 P P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP + 6 P i 6 P Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction Output 1 P G3P (a sugar) Glucose and other organic compounds

Fig. 10-18-3 Input 3 (Entering one at a time) CO 2 Phase 1: Carbon fixation Rubisco 3 P Short-lived intermediate 3 P P 6 P Ribulose bisphosphate 3-Phosphoglycerate (RuBP) P 6 6 ADP ATP 3 ATP 3 ADP Calvin Cycle 6 P P 1,3-Bisphosphoglycerate Phase 3: Regeneration of the CO 2 acceptor (RuBP) 5 P G3P 6 P Glyceraldehyde-3-phosphate (G3P) 6 NADPH 6 NADP + 6 P i Phase 2: Reduction Output 1 P G3P (a sugar) Glucose and other organic compounds

Dehydration is a problem for plants On hot, dry days, plants close stomata, which conserves H 2 O but also limits photosynthesis by reducing CO 2 and causes O 2 to build up These conditions favor a seemingly wasteful process called photorespiration rubisco adds O 2 instead of CO 2 in the Calvin cycle releases CO 2 without producing ATP or sugar Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

C 4 plants minimize the cost of photorespiration by incorporating CO 2 into four-carbon compounds in mesophyll cells bundle-sheath cells, where they release CO 2 that is then used in the Calvin cycle Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon CAM plants open their stomata at night, incorporating CO 2 into organic acids Stomata close during the day, and CO 2 is released from organic acids and used in the Calvin cycle Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 10-20 Sugarcane C 4 Pineapple CAM CO 2 CO 2 Mesophyll cell Organic acid 1 CO 2 incorporated into four-carbon organic acids (carbon fixation) Organic acid Night Bundlesheath cell CO 2 CO 2 Calvin Cycle 2 Organic acids release CO 2 to Calvin cycle Calvin Cycle Day Sugar (a) Spatial separation of steps Sugar (b) Temporal separation of steps

The energy from the sun gets stored as chemical energy Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits Produces the O 2 in our atmosphere Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings