Transcript File
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 Where’s the ATP? carbon + water + energy glucose + oxygen dioxide 6CO2 + 6H2O + light C6H12O6 + 6O2 energy AP Biology endergonic 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… AP Biology uptake from roots 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+ AP Biology + + H + H H+ + H H + H+ H+ H+ + H H Pigments of photosynthesis chlorophyll & accessory Why does this structure make sense? pigments “photosystem” embedded in thylakoid membrane structure function AP Biology 2005-2006 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 Photosynthesis Light reactions light-dependent reactions energy production reactions convert solar energy to chemical energy ATP & NADPH Calvin cycle It’s the Dark Reactions! light-independent reactions sugar production reactions uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6 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 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 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 can’t 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 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 5C 1C 1. Carbon fixation Rubisco -enzyme that Binds CO2 to RuBP 3 ADP PGAL sucrose cellulose etc. CO2 6C 2x 3C 3C x2 PGA 2. Reduction 6 ATP 6 NADPH 6 NADP AP Biology 2x 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 H2O produced O2 as by product 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 Where’s Mufasa? ATP O2 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? What’s 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 Alternative Pathways The Calvin Cycle is the MOST Common Pathway for Carbon Fixation. Plant Species that fix Carbon EXCLUSIVELY through the Calvin Cycle are known as C3 PLANTS. Plants in hot dry environments have a problem with water loss, so they keep their stomata partly closed... this results in: CO2 deficit (Used in Calvin Cycle), and the level of O2 RISES (as Light reactions Split Water Molecules). AP Biology Figure 7.10 C4 plants and CAM plants use an alternate pathway to FIX carbon dioxide from the air. AP Biology Figure 7.11 THE CAM PATHWAY - Plants that use the CAM Pathway open their stomata at night and close during the day. At night, CAM Plants take in CO2 and fix into organic compounds. During the day, CO2 is released from these Compounds and enters the Calvin Cycle. Because they have their stomata open only at night, they grow slow. AP Biology