photosynthesis pt2

• Photosynthesis


  The process by which plants and other organisms use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar

  
• Photosynthesis reaction


  Explain the reaction of photosynthesis

  
• Chloroplast

  • Draw and label the structure of a chloroplast
• Photosynthesis equation


  Learn the balanced form of the overall equation for photosynthesis

  
• Photosynthetic process


  1. Differentiate between light-dependent and light-independent reactions

  2. Calvin cycle and carbon fixation

  3. Recognize what each pathway contributes to photosynthesis

  
• Photosystem


  Define photosystem, antenna complex, and reaction center

  
• Photosystems location


  Recognize where photosystems are located within a plant cell

  
• Antenna complex


  Explain how an antenna complex gathers light energy
• Photosystems and chlorophyll


  Relate the photosystems and the chlorophyll pigment to the photoelectric effect (conversion of light energy to chemical energy)

  
• Light-dependent reactions


  1. NADPH (electrons and proton) is produced

  2. ATP is generated with the help of ATP synthase
• Chloroplast


  • Explain the role of chloroplast membranes and compartments, in the transport of electrons, protons, synthesis of ATP and glucose (G3P) production
• Photochemiosmotic model


  Summarize the photochemiosmotic model of ATP production in chloroplasts and compare it to the mitochondria

  
• Calvin cycle


  Summarize the three main phases of the Calvin cycle
• Photorespiration


  Define photorespiration, compare and show how plants have adapted ways to minimize it (C3, C4 plants and CAM)

  
• Organelles and environment


  Link the exchange of materials between the organelles and the environment for each process
• The Calvin cycle reaction convert inorganic carbon into organic carbon in the form of carbohydrates

  
• Phases of the Calvin cycle

  1. Carbon fixation

  2. Reduction

  3. Regeneration of RuBP

  
• Rubisco


  A large multienzyme complex that catalyzes the fixation of CO2 and RuBP to PGA
• Carbon fixation


  A carbon atom from CO2 is added to a five-carbon molecule (RuBP)
• Reduction


  1. Energy from ATP add a phosphate to the 3 carbon molecule

  2. This phosphate is afterward replaced by and hydrogen atom from NADPH (and electron)
• Regeneration of RuBP


  10 molecule of G3P will be used to regenerate RuBP
• To build a carbohydrate like glucose, the cells use carbon from CO2, reduction potential of NADPH, and energy from ATP

  
• Net equation of the Calvin cycle

  6 CO2 + 18 ATP + 12 NADPH + Water -> 2 G3P + 16 Pi + 18 ADP + 12 NADP+

  
• Photosynthesis - Light-Independent Step

  1. Use carbon from the CO2

  2. Reduction potential of the NADPH provides H+ and electrons to bind to carbon atoms

  3. Energy from ATP produced by the light-dependent step

  
• Calvin Cycle


  6 CO2 + 18 ATP + 12 NADPH + Water → 2 G3P + 16 Pi + 18 ADP + 12 NADP+
• The light-dependent step of photosynthesis produces 1 NADPH and a little more than 1 ATP per pair of electrons (or water molecule)

  
• We need a ratio of 1.5 ATP per NADPH for the Calvin cycle
• Light-Dependent Step: Cyclic Phosphorylation


  1. Light energy absorbed at PS I is used for ATP synthesis rather than NADPH synthesis

  2. High-energy electrons generated are transferred to the cytochrome bf complex rather than to NADP+

  3. The cytochrome bf complex pump H+ from the stroma to the thylakoid lumen

  4. The H+ gradient is used to create ATP by the ATP synthase
• Rubisco catalyzes the fixation of CO2 to RuBP (carboxylation)


  Creates PGA
• Oxidation of RuBP occurs when oxygen levels are relatively high, because O2 and CO2 compete for the same active site on RUBISCO
• At 25°C, photorespiration is 20% of the carboxylation reaction, and at 28°C it is 50%

  
• Stomata


  • Little doors that can open and close to let water and gases go in or out of leaves
  • In hot temperatures, plants will close their stomata to prevent water loss, limiting the entrance of CO2 and exit of O2
• Stomata are closed in high temperature conditions


  Leads to accumulation of O2 and decrease in CO2, increasing photorespiration
• C3 plants


  Temperate plants where the first fixed carbon molecule (PGA) is a 3 carbon molecule
• C4 plants


  Tropical plants that have found ways to avoid the problem of photorespiration by separating the fixation of CO2 and the Calvin cycle into two different cells

  
• C4 Photosynthesis


  1. PEP carboxylase fixes carbon from CO2 to phosphoenol pyruvate (PEP) creating oxaloacetate

  2. Oxaloacetate is transformed to malate and transported to the bundle-sheath cell

  3. Malate is decarboxylated directly at the site of rubisco, allowing for a high concentration of CO2 without the presence of O2

  
• The C4 process requires additional ATP compared to the Calvin cycle alone
• CAM plants


  Tropical plants that have found ways to avoid the problem of photorespiration by separating the fixation of CO2 and the Calvin cycle in the same cells but at different times (night/day)

  
• CAM Photosynthesis


  1. Fixation of CO2 into oxaloacetate (C4) happens at night when stomata are open

  2. Oxaloacetate is transformed into organic acids that accumulate at night

  3. During the day, the organic acids are decarboxylated to provide CO2 for the Calvin cycle while the stomata are closed

  
• CAM photosynthesis also requires additional ATP investment compared to the Calvin cycle alone