BISC221 Lecture12 - Chapter 10 Photosynthesis Overview The...

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Chapter 10 Photosynthesis
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Overview: The Process That Feeds the Biosphere Photosynthesis is the process that converts solar energy into chemical energy Directly or indirectly, photosynthesis nourishes almost the entire living world Autotrophs sustain themselves without eating anything derived from other organisms Autotrophs are the producers of the biosphere, producing organic molecules from CO 2 and other inorganic molecules Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules from water and carbon dioxide
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Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes These organisms feed not only themselves but also the entire living world Heterotrophs obtain their organic material from other organisms Heterotrophs are the consumers of the biosphere Almost all heterotrophs, including humans, depend on photoautotrophs for food and oxygen
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Photosynthesis converts light energy to the chemical energy of food Chloroplasts are organelles that are responsible for feeding the vast majority of organisms Chloroplasts are present in a variety of photosynthesizing organisms Leaves are the major locations of photosynthesis Their green color is from chlorophyll, the green pigment within chloroplasts Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast Through microscopic pores called stomata, CO 2 enters the leaf and O 2 exits
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Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf A typical mesophyll cell has 30-40 chloroplasts The chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana Chloroplasts also contain stroma, a dense fluid Photosynthesis
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Photosynthesis • Photosynthesis converts light energy to the chemical energy of food • Chloroplasts are the sites of photosynthesis in plants • The leaves of plants are the major sites of photosynthesis
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LE 10-3 Leaf cross section Vein Mesophyll Stomata CO 2 O 2 Mesophyll cell Chloroplast 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid space Thylakoid Granum Stroma 1 µm
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Tracking Atoms Through Photosynthesis • Photosynthesis is summarized as: 6 CO 2 + 12 H 2 O + Light energy ----> C 6 H 12 O 6 + 6 O 2 + 6 H 2 O • Chloroplasts split water into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules 6 CO 2 12 H 2 O Reactants: Products: C 6 H 12 O 6 6 H 2 O 6 O 2 Photosynthesis is a redox process in which water is oxidized and carbon dioxide is reduced
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The Two Stages of Photosynthesis Photosynthesis consists of the light reactions (the photo part) and the Calvin cycle (the synthesis part): The light reactions (in the thylakoids) split water, release O 2 , produce ATP, and form NADPH The Calvin cycle (in the stroma) forms sugar from CO 2 , using ATP and NADPH The Calvin cycle begins with carbon fixation, incorporating CO 2 into organic molecules
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LE 10-5_1 H 2 O LIGHT REACTIONS Chloroplast Light
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LE 10-5_2 H 2 O LIGHT REACTIONS Chloroplast Light ATP NADPH O 2
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