AP BIOLOGY PHOTOSYNTHESIS Chapter 10 Light Reactions http://vilenski.org/science/safari/cellstructure/chloroplasts.html AP BIOLOGY PHOTOSYNTHESIS Chapter 10 Light Reactions http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG

different wavelengths as different ___________ wavelengths Sunlight is made up of many different _______________ of light Your eyes “see” different wavelengths as different ___________ wavelengths colors http://www.simontucket.com/_Portfolio/PortLarge/L_Il_Prism.jpg

Visible light is part of electromagnetic spectrum Y O R

pigments Plants gather the sun’s energy with light absorbing molecules called _______________. pigments By: VanderWal

The main energy absorbing molecule in green plants is http://fig.cox.miami.edu/Faculty/Dana/chlorophyll.jpg The main energy absorbing molecule in green plants is __________________ CHLOROPHYLL a

CAROTENOID PIGMENTS appear ORANGE, RED, and YELLOW http://www.rnzih.org.nz/images/gardenimages/carrots_d.jpg CAROTENOID PIGMENTS appear ORANGE, RED, and YELLOW Carotene appears orange Xanthophyll appears yellow http://www.webexhibits.org/causesofcolor/images/content/7C_chlorophyll_in_leaves.jpg

Pigments of photosynthesis Chlorophyll & other pigments embedded in thylakoid membrane arranged in a “photosystem” structure-function relationship

Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of light chlorophyll a absorbs best in red & blue wavelengths & least in green other pigments with different structures absorb light of different wavelengths

WHY ARE PLANTS GREEN? We “see” reflected light Light wavelengths that are reflected bounce back to your eyes . . . so leaves “LOOK” green. Image modified from: http://www.visibledreams.net/Web/color/color_3.html

WHY DON’T WE SEE THE OTHER PIGMENTS? Carotenoids are usually hidden by the presence of chlorophyll

In the fall chlorophyll production shuts down and other pigments “show” http://www.litzsinger.org/weblog/archives/email%20AutumnTrees5%20LREC%20102605.jpg http://sps.k12.ar.us/massengale/ecology_notes_bi.htm

PHOTOSYNTHESIS HAPPENS IN CHLOROPLASTS THYLAKOIDS = sac-like photosynthetic = stack of thylakoids membranes inside chloroplast GRANUM (pl. grana) Image from BIOLOGY by Miller and Levine; Prentice Hall Publishing©2006

SPACES THYLAKOID SPACE (lumen) STROMA cytoplasm Gel-filled space inside chloroplast surrounding thylakoid sac Gel-filled space Inside the thylakoid sac cytoplasm Gel-filled space OUTSIDE chloroplast but inside the cell membrane http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG

PHOTOSYNTHESIS OVERVIEW Pearson Education Inc; Publishing as Prentice Hall

ATP LIGHT DEPENDENT REACTIONS CHARGE UP ENERGY CARRIER = _____ Adenine Phosphate groups Ribose

Energy for cellular work (Energy- consuming) ATP Energy for cellular work (Energy- consuming) Energy from catabolism (Energy- yielding) ADP + P i

NADP+ + 2e- + H+ → NADPH High energy electron carrier = _____________ NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE High energy electron carrier = _____________ NADP+ NADP+ + 2e- + H+ → NADPH

Photosynthesis Light reactions Calvin cycle light-dependent reactions energy production reactions convert solar energy to chemical energy Make ATP & NADPH Calvin cycle light-independent reactions sugar production reactions use chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6

Photosystems of photosynthesis 2 photosystems in thylakoid membrane Both have a REACTION CENTER • CHLOROPHYLL a molecules • PRIMARY ELECTRON ACCEPTOR Surrounded by light-gathering “ANTENNA COMPLEX” • Accessory pigments (chlorophyll b, carotenoids) Collect light energy and pass it on to chlorophyll a Photosystem II P680 = absorbs 680nm wavelength red light Photosystem I P700 = absorbs 700nm wavelength red light

ETC of Photosynthesis Photosystem II Photosystem I Two places where light comes in. Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy. Need to look at that in more detail on next slide

ELECTRON TRANSPORT CHAIN Plastoquinone Cytochrome Plastocyanin Ferredoxin

Light Dependent reactions Electron Transport Chain membrane-bound proteins in organelle electron acceptors NADPH proton (H+) gradient across inner membrane Where’s the double membrane? ATP synthase enzyme Not accidental that these 2 systems are similar, because both derived from the same primitive ancestor.

Chloroplasts transform light energy into chemical energy of ATP use electron carrier NADPH ETC of Photosynthesis Two places where light comes in. Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy. Need to look at that in more detail on next slide

LIGHT DEPENDENT REACTIONS ETC produces from light energy ATP & NADPH go to Calvin cycle PS II absorbs light excited electron passes from chlorophyll to “primary electron acceptor” need to replace electron in chlorophyll enzyme extracts electrons from H2O & supplies them to chlorophyll splits H2O O combines with another O to form O2 O2 released to atmosphere and we breathe easier!

ETC of Photosynthesis to the Calvin Cycle 3 1 H+ 4 H+ PS II absorbs light Excited electron passes from chlorophyll to the primary electron acceptor Need to replace electron in chlorophyll An enzyme extracts electrons from H2O & supplies them to the chlorophyll This reaction splits H2O into 2 H+ & O- which combines with another O- to form O2 O2 released to atmosphere Chlorophyll absorbs light energy (photon) and this moves an electron to a higher energy state Electron is handed off down chain from electron acceptor to electron acceptor In process has collected H+ ions from H2O & also pumped by Plastoquinone within thylakoid sac. Flow back through ATP synthase to generate ATP. 4 H+ ADP + Pi ATP

ETC of Photosynthesis to the Calvin Cycle 3 1 2 H+ 4 H+ ATP ADP + Pi

$$ in the bank… reducing power ETC of Photosynthesis electron carrier 6 to the Calvin Cycle 5 Need a 2nd photon -- shot of light energy to excite electron back up to high energy state. 2nd ETC drives reduction of NADP to NADPH. Light comes in at 2 points. Produce ATP & NADPH $$ in the bank… reducing power

ETC of Photosynthesis split H2O Two places where light comes in. Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy. Need to look at that in more detail on next slide split H2O

MAKING ATP moves the electrons runs the pump pumps the protons forms the gradient drives the flow of protons through ATP synthase attaches Pi to ADP forms the ATP H+ ADP + Pi ATP

Noncyclic Photophosphorylation Light reactions elevate electrons in 2 steps (PS II & PS I) PS II generates energy as ATP PS I generates reducing power as NADPH 1 photosystem is not enough. Have to lift electron in 2 stages to a higher energy level. Does work as it falls. First, produce ATP -- but producing ATP is not enough. Second, need to produce organic molecules for other uses & also need to produce a stable storage molecule for a rainy day (sugars). This is done in Calvin Cycle!

Cyclic photophosphorylation PS I doesn’t pass electron to NADP… it cycles back to ETC & makes more ATP, but no NADPH coordinates light reactions to Calvin cycle Important in maintaining proportion of ATP & NADPH for Calvin Calvin cycle uses more ATP than NADPH X

Photophosphorylation cyclic photophosphorylation noncyclic photophosphorylation

Experimental evidence Where did the O2 come from? radioactive tracer = O18 6CO2 6H2O C6H12O6 6O2 light energy  + Experiment 1 6CO2 6H2O C6H12O6 6O2 light energy  + 6CO2 6H2O C6H12O6 6O2 light energy  + Experiment 2 Proved O2 came from H2O not CO2 = plants split H2O

LIGHT DEPENDENT REACTION Requires ______________ Molecules embedded in ________________________ Made up of __________________ connected by ______________________ & ___________________ Uses light energy to change ADP + P → _______ NADP+ + 2e- + H + → _________ Breaks apart ______ molecules and releases _____________ LIGHT THYLAKOID membranes PHOTOSYSTEMS II & I ELECTRON TRANSPORT CHAIN ATP SYNTHASE ATP NADPH H20 oxygen

LIGHT REACTIONS summary Where did the energy come from? Where did the electrons come from? Where did the H2O come from? Where did the O2 come from? Where did the O2 go? sunlight From chlorophyll; replaced by H2O In through roots Made when water splits Out through stomata

LIGHT REACTIONS summary Where did the H+ come from? Where did the ATP come from? What will the ATP be used for? Where did the NADPH come from? What will the NADPH be used for? Split off of water Produced by ATP synthase during light rxns Make sugar in Calvin cycle Receives e-’s at end of ETC Make sugar in Calvin cycle …stay tuned for the Calvin cycle

PHOTOSYNTHESIS Light-Dependent Reaction Light & Water Oxygen ATP NADPH (CH2O)n Carbon Dioxide Light-Independent Reactions CALVIN CYCLE

http://vilenski.org/science/safari/cellstructure/chloroplasts.html CALVIN CYCLE http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG

*Molecules you need to know Calvin Cycle *Molecules you need to know * * * See Calvin cycle animation X 2

CALVIN CYCLE MOLECULES 5 carbon CO2 acceptor that combines with CO2 in the first step of the Calvin cycle ________________________________ Enzyme that catalyzes the addition of CO2 to RuBP ________________________ 3 carbon sugar produced during the Calvin cycle that can be used to build glucose and other organic molecules ______________________________ Ribulose bisphosphate (RuBP) RuBP carboxylase (RUBISCO) Glyceraldehyde-3-phosphate (G3P)

CALVIN CYCLE ____________ require ____________ (also called _________________________) ____________ require ____________ Happens in _________ between thylakoids NADPH donates _______________ ATP donates _________________ CO2 donates ______________ to make __________________________ LIGHT INDEPENDENT DOES NOT LIGHT STROMA Hydrogen ions + electrons ENERGY Carbon & oxygen glyceraldehyde-3-phosphate (G3P) http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookCHEM2.html

To make one glucose molecule C6H12O6 the Calvin cycle uses _____ molecules of CO2 _____ molecules of ATP _____ molecules of NADPH 6 18 12 Campbell concept check 10.3

CALVIN CYCLE summary Where does the C in G3P come from? Where does the H in G3P come from? Where does the O in G3P come from? Where does the ADP & NADP+ go? Where does the G3P go? CO2 From H2O via NADPH CO2 Back to light reaction to recharge Used to make glucose and other organic molecules

STOMA (pl. STOMATA) GUARD CELLS http://www.cbu.edu/~seisen/Stomata.jpg

PROBLEMS ON HOT DRY DAYS If stomata are open to receive CO2 . . . results in water loss On hot, dry days if plant shuts stomata to conserve water . . . photosynthesis slows http://www.ipm.iastate.edu/ipm/icm/files/images/spider-mite-field.jpg

PHOTORESPIRATION C3 ____ plants (Ex: rice, wheat, soybeans) (1st product of carbon fixation has 3 C’s- 3PG) On hot, dry days when plant shuts stomata plant switches to ______________________ Rubisco adds O2 to Calvin cycle instead of CO2 Product broken down by mitochondria/peroxisomes to release CO2 COUNTERPRODUCTIVE: Makes NO ATP Makes NO sugar Uses ATP Decreases photosynthesis by siphoning molecules from Calvin cycle PHOTORESPIRATION

ALTERNATIVE METHODS of CARBON FIXATION ______ plants (Ex: corn & sugarcane ______ Crassulacean acid metabolism (Ex: succulents, cactus, pineapple,) WAYS TO AVOID DECREASE IN PHOTOSYNTHESIS DUE TO PHOTORESPIRATION CAM SEE ANIMATION

CALVIN CYCLE found in BUNDLE SHEATH CELLS in C4 plants * PEP CARBOXYLASE ________________________ adds CO2 to make a 4 carbon molecule before entering Calvin Cycle

photophosphorylation Process of using H+ gradient to generate ATP = ________________________ (Can refer to ATP made in mitochondria too) Process of creating ATP using a Proton gradient created by the energy gathered from sunlight. Process that consumes oxygen, releases CO2, generates no ATP, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide = ___________________________________ chemiosmosis photophosphorylation photorespiration