pigments AP BIOLOGY PHOTOSYNTHESIS Chapter 10 Light Reactions Visible light is part of electromagnetic spectrum

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1 AP BIOLOGY PHOTOSYNTHESIS Chapter 10 Light Reactions Sunlight is made up of many different wavelengths of light Your eyes see different wavelengths as different colors Visible light is part of electromagnetic spectrum Plants gather the sun s energy with light absorbing molecules called. pigments V I B G Y O R By: VanderWal 1

2 CAROTENOID PIGMENTS appear ORANGE, RED, and YELLOW Carotene appears orange The main energy absorbing molecule in green plants is CHLOROPHYLL a Xanthophyll appears yellow Pigments of photosynthesis 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 Chlorophyll & other pigments embedded in thylakoid membrane arranged in a photosystem structure-function relationship 2

3 WHY ARE PLANTS GREEN? WHY DON T WE SEE THE OTHER PIGMENTS? We see reflected light Light wavelengths that are reflected bounce back to your eyes... so leaves LOOK green. Image modified from: Carotenoids are usually hidden by the presence of chlorophyll In the fall chlorophyll production shuts down and other pigments show PHOTOSYNTHESIS HAPPENS IN CHLOROPLASTS THYLAKOIDS = sac-like photosynthetic membranes inside chloroplast GRANUM (pl. grana) = stack of thylakoids Image from BIOLOGY by Miller and Levine; Prentice Hall Publishing

4 THYLAKOID SPACE (lumen) Gel-filled space Inside the thylakoid sac SPACES STROMA Gel-filled space inside chloroplast surrounding thylakoid sac PHOTOSYNTHESIS OVERVIEW cytoplasm Gel-filled space OUTSIDE chloroplast but inside the cell membrane Pearson Education Inc; Publishing as Prentice Hall LIGHT DEPENDENT REACTIONS CHARGE UP ENERGY CARRIER = ATP Phosphate groups Adenine ATP Energy for cellular work (Energy- consuming) Energy from catabolism (Energy- yielding) ADP + P i Ribose 4

5 NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE High energy electron carrier = NADP + NADP + + 2e - + H + NADPH Photosynthesis Light reactions 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 CO 2 & synthesize C 6 H 12 O 6 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 ETC of Photosynthesis Photosystem I Photosystem II P 680 = absorbs 680nm wavelength red light Photosystem I P 700 = absorbs 700nm wavelength red light 5

6 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 H+ H + H + H+H+ H+ ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP use electron carrier NADPH 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 H 2 O & supplies them to chlorophyll splits H 2 O O combines with another O to form O 2 O 2 released to atmosphere and we breathe easier! 6

7 ETC of Photosynthesis ETC of Photosynthesis electron carrier 6 5 to the Calvin Cycle split H 2 O $$ in the bank reducing power MAKING ATP Noncyclic Photophosphorylation moves the electrons runs the pump pumps the protons forms the gradient drives the flow of protons through ATP synthase attaches P i to ADP forms the ATP ADP + P i ATP H + H + H + H + H + H + H+ H + H + Light reactions elevate electrons in 2 steps (PS II & PS I) PS II generates energy as ATP PS I generates reducing power as NADPH 7

8 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 O 2 come from? radioactive tracer = O 18 Experiment 1 6CO 2 + 6H 2 O + light C 6 H 12 O 6 6O energy + 2 Experiment 2 6CO 2 + 6H 2 O + light C 6 H 12 O 6 6O energy + 2 Proved O 2 came from H 2 O not CO 2 = plants split H 2 O LIGHT DEPENDENT REACTION Requires LIGHT Molecules embedded in THYLAKOID membranes Made up of PHOTOSYSTEMS II & I connected by ELECTRON TRANSPORT CHAIN & ATP SYNTHASE Uses light energy to change ADP + P ATP NADP + + 2e - + H + NADPH Breaks apart H 2 0 molecules and releases oxygen 8

9 LIGHT REACTIONS summary Where did the energy come from? sunlight Where did the electrons come from? From chlorophyll; replaced by H 2 O Where did the H 2 O come from? In through roots Where did the O 2 come from? Made when water splits Where did the O 2 go? Out through stomata LIGHT REACTIONS summary Where did the H + come from? Split off of water Where did the ATP come from? Produced by ATP synthase during light rxns What will the ATP be used for? Make sugar in Calvin cycle Where did the NADPH come from? Receives e - s at end of ETC What will the NADPH be used for? Make sugar in Calvin cycle stay tuned for the Calvin cycle Light & Water PHOTOSYNTHESIS Light-Dependent Reaction Oxygen CALVIN CYCLE ATP NADPH Carbon Dioxide Light-Independent Reactions CALVIN CYCLE (CH 2 O) n 9

10 * Calvin Cycle * Molecules you * need to know CALVIN CYCLE MOLECULES 5 carbon CO 2 acceptor that combines with CO 2 in the first step of the Calvin cycle Ribulose bisphosphate (RuBP) Enzyme that catalyzes the addition of CO 2 to RuBP RuBP carboxylase (RUBISCO) * X 2 See Calvin cycle animation 3 carbon sugar produced during the Calvin cycle that can be used to build glucose and other organic molecules Glyceraldehyde-3-phosphate (G3P) CALVIN CYCLE (also called ) LIGHT INDEPENDENT DOES NOT require LIGHT Happens in STROMA between thylakoids NADPH donates Hydrogen ions + electrons ATP donates ENERGY CO 2 donates Carbon & oxygen to make glyceraldehyde-3-phosphate (G3P) To make one glucose molecule C 6 H 12 O 6 the Calvin cycle uses 6 molecules of CO 2 18 molecules of ATP 12 molecules of NADPH Campbell concept check

11 CALVIN CYCLE summary STOMA (pl. STOMATA) Where does the C in G3P come from? Where does the H in G3P come from? Where does the O in G3P come from? CO 2 From H 2 O via NADPH CO 2 Where does the ADP & NADP + go? Where does the G3P go? Back to light reaction to recharge Used to make glucose and other organic molecules GUARD CELLS PROBLEMS ON HOT DRY DAYS If stomata are open to receive CO 2... results in water loss On hot, dry days if plant shuts stomata to conserve water... photosynthesis slows C 3 plants (Ex: rice, wheat, soybeans) (1 st product of carbon fixation has 3 C s- 3PG) On hot, dry days when plant shuts stomata plant switches to PHOTORESPIRATION Rubisco adds O 2 to Calvin cycle instead of CO 2 Product broken down by mitochondria/peroxisomes to release CO 2 COUNTERPRODUCTIVE: Makes NO ATP Makes NO sugar Uses ATP Decreases photosynthesis by siphoning molecules from Calvin cycle 11

12 ALTERNATIVE METHODS of CARBON FIXATION C 4 plants (Ex: corn & sugarcane CAM Crassulacean acid metabolism (Ex: succulents, cactus, pineapple,) WAYS TO AVOID DECREASE IN PHOTOSYNTHESIS DUE TO PHOTORESPIRATION SEE ANIMATION CALVIN CYCLE found in BUNDLE SHEATH CELLS in C 4 plants * PEP CARBOXYLASE adds CO 2 to make a 4 carbon molecule before entering Calvin Cycle Process of using H + gradient to generate ATP chemiosmosis = (Can refer to ATP made in mitochondria too) Process of creating ATP using a Proton gradient created by the energy gathered from sunlight. photophosphorylation = 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 photorespiration = 12