Photosynthesis: Life from Light AP Biology How are
Photosynthesis: Life from Light AP Biology How are they connected? Heterotrophs and Autotrophs making energy & organic molecules from ingesting organic molecules glucose + oxygen carbon + water + energy dioxide C6H12O6 + 6O2 6CO2 + 6H2O + ATP exergonic Autotrophs
making energy & organic molecules from light energy Wheres the ATP? carbon + water + energy glucose + oxygen dioxide 6CO2 + 6H2O + light C6H12O6 + 6O2 energy AP Biology endergonic Photoautotrophs AP Biology
Plant structure Obtaining raw materials sunlight leaves = solar collectors CO2 stomates = gas exchange Found under leaves H2O uptake from roots
Nutrients N, P, K, S, Mg, Fe uptake from roots AP Biology 2005-2006 Plant structure Chloroplasts double membrane stroma thylakoid sacs grana stacks Chlorophyll & ETC in thylakoid membrane
H+ gradient built up within thylakoid sac H +H + H H H + H+ H+ HH+ H+ H + AP Biology + + + Pigments of photosynthesis
chlorophyll & accessory Why does this structure make sense? pigments photosystem embedded in thylakoid membrane structure function AP Biology 2005-2006 Photosynthesis = Light Reactions + Calvin Cycle photo
AP Biology synthesis Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of light chlorophyll a (dominant pigment) absorbs best in red & blue wavelengths & least in green other pigments with different structures absorb light of different wavelengths Why are
plants green? AP Biology Photosynthetic pigments Pigments absorb different of light chlorophyll absorb violet-blue/red light, reflect green chlorophyll a (blue-green): light reaction, converts solar to chemical E chlorophyll b (yellow-green): conveys E to chlorophyll a carotenoids (yellow, orange): photoprotection, broaden color spectrum for
photosynthesis Types: xanthophyll (yellow) & carotenes (orange) anthocyanin (red, purple, blue): photoprotection, antioxidants AP Biology Photosynthesis Light reactions light-dependent reactions energy production reactions convert solar energy to chemical energy ATP & NADPH
Calvin cycle Its the Dark Reactions! light-independent reactions sugar production reactions uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6 AP Biology Light Reactions Summary: Light energy splits H2O to O2 releasing high energy electrons
(e-) Movement of e- used to generate ATP Electrons end up on NADP+, reducing it to NADPH AP Biology Light reactions Electron Transport Chain (like cell respiration!) membrane-bound proteins in organelle electron acceptor NADPH proton (H+) gradient across inner membrane ATP synthase
enzyme AP Biology 2005-2006 Photosystem: reaction center & light-harvesting complexes (pigment + protein) AP Biology Photosystems 2 photosystems in thylakoid membrane act as light-gathering antenna complex Photosystem II chlorophyll a
P680 = absorbs 680nm wavelength red light Photosystem I chlorophyll b P700 = absorbs 700nm wavelength red light AP Biology reaction center ETC of Photosynthesis ETC produces from light energy
ATP & NADPH NADPH (stored energy) goes to Calvin cycle PS II absorbs light AP Biology excited electron passes from chlorophyll to primary electron acceptor at the REACTION CENTER. splits H2O (Photolysis!!) O2 released to atmosphere ATP is produced for later use ETC of Photosynthesis Photosystem II Photosystem I AP Biology
Electron Flow Two routes for electron flow: A. Linear (noncyclic) electron flow B. Cyclic electron flow AP Biology Light Reaction (Linear electron flow) 1.Chlorophyll excited by light absorption 2.E passed to reaction center of Photosystem II (protein + chlorophyll a) 3.e- captured by primary electron acceptor
Redox reaction e- transfer e- prevented from losing E (drop to ground state) 4.H2O is split to replace e- O2 formed AP Biology 5.e- passed to Photosystem I via ETC 6.E transfer pumps H+ to thylakoid space 7.ATP produced by photophosphorylation 8.e- moves from PS Is primary electron acceptor to 2nd ETC 9.NADP+ reduced to NADPH AP Biology 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 AP Biology 2005-2006 Cyclic photophosphorylation If PS I cant pass electron to NADP,
it cycles back to PS II & makes more ATP, but no NADPH AP Biology X coordinates light reactions to Calvin cycle Calvin cycle uses more ATP than NADPH 2005-2006
From Light reactions to Calvin cycle Calvin cycle Chloroplast stroma Need products of light reactions to drive synthesis reactions ATP NADPH What is there left to do? Make sugar! AP Biology 2005-2006
Calvin Cycle: Uses ATP and NADPH to convert CO2 to sugar Occurs in the stroma Uses ATP, NADPH, CO2 Produces 3-C sugar G3P (glyceraldehyde3-phosphate) Three phases: 1. 2. 3. AP Biology Carbon fixation Reduction Regeneration of RuBP (CO2 acceptor) From CO2 C6H12O6 CO2 has very little chemical energy
fully oxidized C6H12O6 contains a lot of chemical energy reduced endergonic Reduction of CO2 C6H12O6 proceeds in many small uphill steps each catalyzed by specific enzyme using energy stored in ATP & NADPH AP Biology Calvin cycle 3. Regeneration of RuBP
ribulose bisphosphate RuBP 3 ATP PGAL to make glucose sucrose cellulose etc. CO2 1. Carbon fixation Rubisco
-enzyme that Binds CO2 to RuBP 3 ADP PGAL 5C 1C 6C 2x 3C 3C x2 PGA 2. Reduction
6 NADPH 6 NADP AP Biology 2x 6 ATP 3C 6 ADP Calvin cycle PGAL important intermediate Six turns of Calvin Cycle = 1 glucose PGAL
AP Biology glucose carbohydrates lipids amino acids nucleic acids Summary Light reactions produced ATP produced NADPH consumed H O 2 produced O as by product 2 Calvin cycle consumed CO2 produced PGAL
regenerated ADP regenerated NADP AP Biology ADP NADP Factors that affect Photosynthesis Enzymes are responsible for several photosynthetic processes, therefore, temperature and pH can affect the rate of photosynthesis. The amount and type of light can affect the rate. A shortage of any of the reactants,CO2 and/or H2O, can affect the rate.
AP Biology Supporting a biosphere On global scale, photosynthesis is the most important process for the continuation of life on Earth each year photosynthesis synthesizes 160 billion tons of carbohydrate heterotrophs are dependent on plants as food source for fuel & raw materials AP Biology Energy cycle sun Photosynthesis
CO2 H 2O glucose Cellular Respiration The Great Circle of Life! AP Biology Wheres Mufasa? ATP O2 Photosynthesis involves both Light
ENERGY Light Reaction in which stored in O22 evolved H22O split m ec by ha of nis m
organic molecules chemiosmosis s energized s pa wn electrons do Calvin Cycle CO22 fixed to RuBP Reduce NADP+ to C33
phosphorylated ETC NADPH and reduced g n i s u to form regenerate G3P ATP RuBP using in process called photophosphorylation AP Biology
glucose & other carbs Alternative mechanisms of carbon fixation have evolved in hot, arid climates Photorespiration Metabolic pathway which: Uses O 2 & produces CO2 Uses ATP No sugar production (rubisco binds O 2 breakdown of RuBP) Occurs on hot, dry bright days when stomata close (conserve H2O) Why? Early atmosphere: low O2, high CO2?
AP Biology Evolutionary Adaptations 1.Problem with C3 Plants: CO2 fixed to 3-C compound in Calvin cycle Ex. Rice, wheat, soybeans Hot, dry days: partially close stomata, CO2 AP Biology
Photorespiration photosynthetic output (no sugars made) 2.C4 Plants: CO2 fixed to 4-C compound Ex. corn, sugarcane, grass Hot, dry days stomata close 2 cell types = mesophyll & bundle sheath cells mesophyll : PEP carboxylase fixes CO2 (4-C), pump CO2 to bundle sheath
bundle sheath: CO2 used in Calvin cycle photorespiration, sugar production WHY? Advantage in hot, sunny areas AP Biology C4 Leaf Anatomy AP Biology 3.CAM Plants:
Crassulacean acid metabolism (CAM) NIGHT: stomata open CO2 enters converts to organic acid, stored in mesophyll cells DAY: stomata closed light reactions supply ATP, NADPH; CO2 released from organic acids for Calvin cycle Ex. cacti, pineapples, succulent (H2Ostoring) plants WHY? Advantage in arid conditions AP Biology LIGHT REACTIONS AP Biology Calvin cycle
Mitochondria AP Biology Chloroplast Comparison RESPIRATION Plants + Animals Needs O2 and food Produces CO2, H2O and ATP, NADH Occurs in mitochondria membrane & matrix Oxidative phosphorylation Proton gradient across membrane AP Biology
PHOTOSYNTHESIS Plants Needs CO2, H2O, sunlight Produces glucose, O2 and ATP, NADPH Occurs in chloroplast thylakoid membrane & stroma Photorespiration Proton gradient across membrane Summary of photosynthesis 6CO2 + 6H2O + light C6H12O6 + 6O2 energy
Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the H2O go? Where did the energy come from? Whats the energy used for? What will the C6H12O6 be used for? Where did the O2 come from? Where will the O2 go? What else is involved that is not listed in this equation? AP Biology 2005-2006
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