Photosynthesis

Light energy PHOTOSYNTHESIS 6 CO 2 6+ H2OH2O Carbon dioxideWater C 6 H 12 O 6 6+ O2O2 GlucoseOxygen gas Photosynthesis

–Human demand for energy Fossil fuel supplies? –Energy plantations Biomass energy

Photoautotrophs –C source? –Energy source? Heterotrophs –C source? –Energy source? Carbon and Energy

Photoautotrophs Figure 7.1A–D

Green parts… –Chloroplasts (stroma and thylakoids) –Stomata Leaf Cross Section Leaf Mesophyll Cell Mesophyll Vein Stoma CO 2 O2O2 Chloroplast Grana Stroma TEM 9,750  Stroma Granum Thylakoid space Outer membrane Inner membrane Intermembrane space LM 2,600  Where does PS happen?

By splitting water Where does O 2 come from?

Redox processes Reduction Oxidation 6 O 2 6 H 2 O Reduction Oxidation 6 O 2 6 CO 2  6 H 2 OC 6 H 12 O 6   6 CO 2  Just like respiration?

Linked Processes Photosynthesis Energy-storing Releases O 2 Requires CO 2 Aerobic Respiration Energy-releasing Requires O 2 Releases CO 2

2 stages The light reactions… –Energy capture –produce O 2 The Calvin cycle –Uses CO 2 –Makes sugar The Coenzymes –ATP –NADPH Overview Light CO 2 H2OH2O Chloroplast LIGHT REACTIONS (in thylakoids) CALVIN CYCLE (in stroma) NADP + ADP +P ATP NADPH OSugar Electrons

Visible Light Increasing energy 10 –5 nm10 –3 nm 1 nm 10 3 nm10 6 nm 1 m 10 3 m Gamma rays X-raysUVInfrared Micro- waves Radio waves Visible light nm Wavelength (nm) Transmitted light Absorbed light Reflected light Light Chloroplast 380

Pigments Colors? Wavelengths not absorbed Chlorophylls a and b Carotenoids

Chlorophylls Wavelength absorption (%) Wavelength (nanometers) chlorophyll b chlorophyll a

T.E. Englemann’s Experiment

Photons Packets of light energy Shortest wavelength (blue-violet light) = highest energy

Strike chlorophyll in photosystem Excite an electron Figure 7.7B, C Energy of electron Photon Excited state Heat Photon (fluorescence) Ground state Chlorophyll molecule e–e– Photosystem Light-harvesting complexes Reaction center Primary electron acceptor e–e– To electron transport chain Pigment molecules Chlorophyll a molecule Transfer of energy Photon Thylakoid membrane Photons and Photosystems

Photon energy transfer to reaction- center Excites electron Which is taken by the primary electron acceptor Which leads to the ETC Energy of electron Photon Excited state Heat Photon (fluorescence) Ground state Chlorophyll molecule e–e– Photosystem Light-harvesting complexes Reaction center Primary electron acceptor e–e– To electron transport chain Pigment molecules Chlorophyll a molecule Transfer of energy Photon Thylakoid membrane

Photosystem: Harvester Pigments When excited by light energy:

Electron Transfer Chain Uses electrons from reaction center Powers H+ pump to produce ATP Produces NADPH Thylakoid space Photon Stroma Thylakoid membrane 1 Photosystem II e–e– P680 2 H2OH2O O2O2 H+H+ 3 ATPElectron transport chain Provides energy for synthesis of by chemiosmosis 4 Photosystem I Photon P700 e–e– 5 + NADP + H+H+ NADPH 6

–Electrons move from photosystem II to I Make ATP –Electrons from photosystem I Reduce NADP + to NADPH Figure 7.8B e–e– ATP Mill makes ATP Photon Photosystem II Photosystem I NADPH e–e– e–e– e–e– e–e– e–e– e–e– Electron Transfer Chain

ATP Production Chloroplast Stroma (low H + concentration) Light NADP + + H+H+ NADPH H+H+ H+H+ H+H+ H+H+ ATP P ADP + Thylakoid membrane H2OH2O 1 2 O2O2 2 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Photosystem II Electron transport chain Photosystem I ATP synthase Thylakoid space (high H + concentration) +

They put the “synthesis” in photosynthesis Calvin-Benson cycle In stroma Light-Independent Reactions

Calvin-Benson Cycle Overall reactants CO 2 ATP NADPH Overall products Glucose ADP NADP + Cyclic! RuBP is regenerated

Figure 7.14_4

1 st stable molecule is 3C PGA C3 plants: tomatoes, petunias, roses, daisies, avocados C3 Plants

Hot, dry days what happens? Inside leaf? –O 2 increases –CO 2 drops PS rate?

C4 Pathway CO 2 miner 4C oxaloacetate forms in bundle sheath cells Grasses

CAM Plants Opens stomata at night Forms 4C compound Release CO 2 Succulents and cacti Slow growing

C4 and CAM

Greenhouse Effect? What is the role of PS in global warming?

–Excess CO 2 in the atmosphere Sunlight ATMOSPHERE Some heat energy escapes into space Radiant heat trapped by CO 2 and other gases Greenhouse Effect

Question of the Day Scientists at Stanford University conducted a study on California grasslands. They looked at the effects of increased levels of CO 2, soil nitrogen, and temperature (modeling our future) on plant growth. What did they find?