Notes for Test 2

Notes for Test 2 - Chapter 6 Where it Starts Photosynthesis...

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Chapter 6 Where it Starts –Photosynthesis Photosynthesis makes food ( sugar ) out of CO2 and H2O 6.1 Sunlight as an Energy Source A. Properties of Light 1. Organisms use only a small range of wavelengths for photosynthesis and vision, including color. 2. Light is packaged as photons , which vary in energy . (use for light, sight, color) B. Pigments- The Rainbow Catchers 1. Pigment molecules in plants are on the thylakoid membranes and absorb photons . 2. Chlorophyll A and B pigments absorb in blue and red, but reflect green to our eyes. 3. Other pigments reflect yellow, oranges, red, etc. as seen in autumn leaves. 6.2 What is Photosynthesis and Where does it Happen? A. Two stages of reactions 1. Light-DEpendent reactions convert light energy to ATP (plant ATP) a. H2O is split to release O2 . b. NADP+ (plant vitamin) picks up electrons to become NADPH (used later) 2. Light INpendent reactions (anytime) assemble sugars using ATP, NADPH, and CO2. 3. Equation for Glucose formation: H2O + CO2 O2 + C6 H12 O6 + H2O Reactants Sunlight B. A look Inside the chloroplast 1. Photosynthesis occurs in chloroplast a. Thylakoids, stacks of interconnected discs , surrounded by the stroma; first reactions occur here. b. Stroma , semifluid interior is site for the second series of reactions. 2. Pigment (chlorophyll) clusters in thylakoid membranes (photo systems) trap sun’s energy . C. Photosynthesis changed the Biosphere 1. O2 by-product began accumulating in Earth’s atmosphere where 3.2 billon years ago, paving way for evolution for aerobic organisms 6.3 Light-Dependent Reactions A. Transducing the Absorbed Energy 1. Pigments in Thylakoid “harvest” photon energy from sunlight . a. Absorbed energy boosts electrons to a higher level.
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b. Electrons will eventually return to lower level but in meantime are passed along in the membrane. 2. The movement of electrons along the electron transfer chain (ETC) is first step in the light-dependent reactions . B. Making ATP and NADPH 1. ETC move e- and H+ from the stroma (fluid) into the thylakoid (disk space) a. H+ are crowded inside thylakoid b. As H+ flow out through channels into stroma, ATP synthase enzymes join P1 + ADP ATP (energized molecule) 2. Simultaneously, H2O splits to O2 (diffuses out) and still more H+ to accumulate inside thylakoid 3. Additionally, e- & H+ are also transferred to NADP to form NADPH 6.5 Light - Independent Reactions : The Sugar Factory A. These reactions are known as the Calvin - Benson cycle. 1. Participates in the synthesis of carbs are: a. ATP , which provides energy b. NADPH, which provides H+ & e- 2. Reactions take place in the stroma; NOT dependent on sunlight B. CO2 diffuses into a leaf ; then across the PM of the photosynthetic cell 1. Rubisco (enzyme) joins CO2 to RuBP to form molecules of PGA . 2. Each PGA then receives a P1 from
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This note was uploaded on 04/08/2008 for the course BISC 101 taught by Professor Sellers during the Fall '07 term at LA Tech.

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Notes for Test 2 - Chapter 6 Where it Starts Photosynthesis...

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