1 Review Summarize what happens during the light dependant reactions 2 Explain How do each of the three primary factors affect the rate of photosynthesis 3 Review What are the different ways that plants cope with water shortages CH 8 PHOTOSYNTHESIS 8.3 The Process of Photosynthesis Why do chloroplasts contain so many membranes? Membranes are the key to capturing light energy. Light Dependant Reactions: Generating ATP and NADPH Photosystems Series of proteins in the thylakoid that absorb sunlight and make high-energy electrons. Electron Transport Chain Series of electron carriers that shuttle high-energy electrons during ATP-generating reactions Electron Transport Chain (ETC). Photosystem II Light energy is absorbed by electrons High energy electrons move through the ETC. Photosystem II Thylakoid provides new electrons from water Water breaks up into 2 electrons, 2 H+ ions, and 1 oxygen atom. Photosystem II 2 electrons replace the high-energy electrons that have been lost to ETC H+ ions released inside thylakoid Oxygen is released into the air. Photosystem II Energy from electrons is used by proteins in ETC to pump H+ ions from the stroma into the thylakoid space. Photosystem II The ETC gives electrons to Photosystem I. Photosystem I Electrons used energy to pump H+ ions so have less energy Photosystem I uses energy from light to reenergize the electrons. Photosystem I After 2nd ETC, NADP+ molecules in the stroma pick up high-energy electrons and H+ ions at the outer surface of the thylakoid membrane to become NADPH. Hydrogen Ion Movement and ATP Formation H+ ions accumulate within the thylakoid space from splitting water and pumping them across. Hydrogen Ion Movement and ATP Formation Gradient of H+ ions Charge and concentrations. Hydrogen Ion Movement and ATP Formation H+ ions cannot directly cross membane ATP synthase that allows H+ ions to pass through Causes it to rotate and bind ADP and a phosphate. Protein Hydrogen Ion Movement and ATP Formation Produces NADPH and ATP. The Light-Independent Reactions: Producing Sugars Called the Calvin Cycle Plants use ATP and NADPH to build stable highenergy carbohydrate compounds that can be stored for a long time. Carbon Dioxide Enters the Cycle Carbon dioxide molecules enter the Calvin cycle from the atmosphere Combine CO2 with 5-carbon compounds 6 CO2 enter, twelve 3-carbon compounds are produced. Enzymes convert the 3carbon compounds into higher-energy forms using ATP and NADPH. Sugar Production Two of the 3-carbon molecules are removed to make sugar. Sugar Production Remaining ten 3carbon molecules are converted back into six 5-carbon molecules Combine with the new CO2 to start the next cycle. ADP ATP Summary of the Calvin Cycle Uses 6 molecules of carbon dioxide to produce a single 6carbon sugar. ADP ATP Energy for the reactions is supplied by compounds produced in the light-dependent reactions. ADP ATP Sugars are used by the plant for energy needs and to build other macromolecules for growth and development. ADP ATP Factors Affecting Photosynthesis Temperature Light intensity Water availability. Temperature Enzymes work best between 0°C and 35°C Lower temps slow enzymes Higher temps denature enzymes. Light Intensity High light intensity increases the rate of photosynthesis There is a maximum to light intensity increasing photosynthesis. Water Availability Water is needed in the reaction Water shortage can stop reaction Certain plants have special adaptations C4 plants CAM plants. C4 Photosynthesis Very good and getting CO2 Uses a 4 carbon molecule Requires added energy Corn, sugar cane, and sorghum. CAM Plants Open their leaves at night and trap CO2 Seal leaves shut during day to conserve water and use trapped CO2 Pineapple trees and many desert cacti.