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Photosynthesis and Energy Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Photosynthesis reaction solar energy chemical energy. LIGHT CO2 + 2H2A (CH2O) + H2O +2A LIGHT CO2 + 2H2S (CH2O) + H2O + 2S LIGTH 3CO2 + 6H2O C3H6O3 + 3O2 + 3H2O Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Why is photosynthesis important? • Photosynthesis is arguably the most important biological process on earth. • Production of sugars • Liberation of oxygen • Responsible for removal of ~ 200 billion tons of C from the atmosphere yearly. • Leaves, flowers, seeds, roots, fruits, bark, pollen, etc. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Thylacoid: Minimum unit inside the chloroplast containing chlorophyll Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Electromagnetic Spectrum high energy short wavelength gamma rays x-rays low energy long wavelength ultraviolet infrared microwaves radiowaves visible light Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 8.2 A substance that absorbs light is known as a pigment. Color is associated with the concept of light absorption. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Primary photosynthetic pigment : chlorophyll a Accessory pigments: chlorophyll b, chlorophyll c, carotenoids, (carotens and xanthophylls) and phycobilins (phycoerythrin and phycocyanin). Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. carotens and xanthophylls A big number of plants drop their leaves and twigs and go dormant during dry spells. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. phycobilins Abundant red algae and cianobacteria Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Electrons (ē) are boosted As the ē to the ground state the energy released would be: a) Converted completely or partially to heat (fluorescence) b) The energy can pass from one excited chlorophyll to another… c) A high energy ē is transferred to an ē receptor chain. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Stages of Photosynthesis • There are two primary stages to photosynthesis. light-dependent reactions: Energy-transduction reactions light-independent reactions: Carbon fixation reactions Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Stage 1: The Steps of the Light Reactions • In the first stage, called the light reactions, electrons derived from water are energetically boosted by the power of sunlight. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Stage 1: The the Light Reactions Stage 1:Steps The of Steps of the Light Reactions sunlight photosystem I photosystem II Water is split, yielding both electrons and oxygen. The electrons move through the light reactions. The oxygen is what organisms such as ourselves breathe in. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Photosystem II is located in the grana Photosystem I and ATP Synthase are located mainly stroma tylakoids and outer portions of the grana Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Stage 2: The Calvin Cycle • In this second stage, the Calvin cycle, the electrons are brought together with carbon dioxide and a sugar. Carbon + ATP +NADPH ----------Glucose and other derivatives Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Stage 2: The Calvin Cycle Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. G3P • G3P can be used for energy or for plant growth. • Everything in the plant ultimately is derived from this sugar, in association with minerals and water that the plant absorbs through its roots. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Photorespiration C4 plants Saturate CO2 into mesophyll cells Oxaloacetate C4 = oxaloacetate PEP carboxylase (PEPCase) Requires additional energy corn sugarcane PEPCase PEP + CO2 Oxaloacetate Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Different metabolic pathways C3 vs. C4 Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. C4 plants efficiency Photosynthesizes faster than C3 plants under high light intensity and high temperatures • CO2 is delivered directly to RUBISCO. • Oxygen don’t undergo photorespiration. Has better water use efficiency • PEP Carboxylase brings in CO2 faster. • Not need to keep stomata open as much. • Less water lost by transpiration for the same amount of CO2 gain for photosynthesis. C4 plants include several thousand species in at least 19 plant families. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. CAM (crassulacean-acid metabolism) Called CAM after the plant family in which it was first found (Crassulaceae) and because the CO2 is stored in the form of an acid before use in photosynthesis. CO2 malate PEP-case The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released to RUBISCO for photosynthesis Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Crassulaceae tissue ★ Substomatal chamber Protected stoma Compact mesophyll Tissue for water storage Deep cuticule Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. CAM Plants CAM plants include many succulents such as cactuses and agaves and also some orchids and bromeliads Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. CAM efficiency Commonly, stomata are open at night when transpiration rates are lower CAM plants can just leave their stomata closed night and day. • Oxygen given off in photosynthesis is used for respiration • CO2 given off in respiration is used for photosynthesis. The plant to survive dry spells, and it allows the plant to recover very quickly when water is available. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Attendance Where does the oxygen come from that is released during the process of photosynthesis? Why is water necessary for the overall process of photosynthesis? Why are the light-dependent reactions necessary for photosynthesis? What is the function and characteristics of peroxisomes? Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.