Photosynthesis

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Author:
sweetz2go
ID:
45618
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Photosynthesis
Updated:
2010-11-08 02:20:04
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Biology
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Photosynthesis
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  1. sWhat is the general chemical equaion for photosynthesis?
  2. Explain why photosynthesis is an example of a redox reduction.
    • reduction: gain electrons, shifting of electrons towords atom
    • oxidation: loses electrons, shifting of electrons away from atom

    carbon is being reduced while oxygen is being oxidized
  3. Define Autotrophs.
    organisms that make their own food (sugar) using sunlight by process of photosynthesis
  4. Where does photosynthesis occur in autotrophs?
    plants and algae -> in chloroplasts

    cyanobacteria -> cell membrane
  5. where does the light reaction of photosynthesis occur?
    • light reaction produces ATP/NADP + H
    • - it occurs at the thlakoid structure

  6. describe the roles of photosystems 1 and 2 in the light reaction.
    Photosystem 2( produces ATP )

    photosystem 1 produces NADPH,

    • To begin photosynthesis, the chlorophyll molecule in photosystem II is
    • excited by sunlight and the energy produced helps to break down a water
    • molecule (H2O) into ½O2 (with electrons removed) and 2H+. The removed
    • electrons are excited by the light energy. When the electrons prepare to
    • come to their rest state, they go through an oxidative phosphorylation
    • process and produces an ATP molecule.

    • As the electrons are coming to a resting state, they are excited again
    • in photosystem I and raised to a even higher energy state. The excited
    • electrons are then used to produce NADP+ + H+. The highly energetic
    • NADPH molecule is then fed into the Calvin Cycle to conduct carbon
    • fixation.
  7. explain, in detail, the light reaction of photosynthesis.
    • 1. As photons are absorbed
    • by pigment molecules in the antenna complexes of Photosystem II, excited electrons
    • from the reaction center are picked up by the primary electron acceptor of the
    • Photosystem II electron transport chain. During this process, Photosystem II
    • splits molecules of H2O into 1/2 O2, 2H+, and
    • 2 electrons. These electrons continuously replace the electrons being lost by
    • the P680 chlorophyll a molecules in the reaction centers of the Photosystem
    • II antenna complexes.
    • 2. During this process,
    • ATP is generated by the Photosystem II electron transport chain and chemiosmosis.
    • According to the chemiosmosis theory, as the electrons are transported down
    • the electron transport chain, some of the energy released is used to pump protons
    • across the thylakoid membrane from the stroma of the chloroplast to the thylakoid
    • interior space producing a proton gradient or proton motive force. As the accumulating
    • protons in the thylakoid interior space pass back across the thylakoid membrane
    • to the stroma through ATP synthetase complexes, this proton motive force is
    • used to generate ATP from ADP and Pi.
    • 3. Meanwhile, photons are
    • also being absorbed by pigment molecules in the antenna complex of Photosystem
    • I and excited electrons from the reaction center are picked up by the primary
    • electron acceptor of the Photosystem I electron transport chain. The electrons
    • being lost by the P700 chlorophyll a molecules in the reaction centers
    • of Photosystem I are replaced by the electrons traveling down the Photosystem
    • II electron transport chain. The electrons transported down the Photosystem
    • I electron transport chain combine with 2H+ from the surrounding
    • medium and NADP+ to produce NADPH + H+.
  8. explain 3 ways the hydrgen ion concentration gradient across the thylakoid membrance is established.
    • 1. splitting of water, generating H+
    • 2. Add more H+, pumping of proton pumps
    • 3. outside of stroma NADP+ picked up
    • - reduce Hydrogen conc. difference in stroma
  9. Where exactly does the calvin cycle of photosynthesis occur?
    stroma
  10. Explain how the calvin cycle reduces carbon dioxide to form sugar.
    • RUBISCO attaches CARBON to RuBP
    • First an enzyme (ribulose biphosphate carboxylase)
    • causes carbon dioxide to combine with ribulose biphosphate (RuBP) to form
    • a six-carbon compound that quickly decomposes to give two molecules of 3-phospho-glycerate
    • (a three-carbon compound). Then, after being changed to glyceraldehyde 3-phosphate
    • (G3P), this re-forms ribulose biphosphate with the release of the sugars
    • fructose and glucose.
    • These sugars are used in respiration
    • or as a building block in making starch and
    • cellulose

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