BIO 105-03

Bio 105 Lecture 9 Notes
I. Photosynthesis Equation Summary

II. Process 1: Light-DEPENDENT Reactions
A. Basic Info

  • absolutely requires light to occur
  • occurs in grana membrane of chloroplast
  • part 1: light energy excites electrons in chlorophyll
    • electrons come from breaking apart h2o
      • frees hydrogens for making glucose
      • releases oxygen gas as waste
    • part 2: excited electrons’ energy used to make ATP and NADPH

B. Chlorophyll and Photosystems
1. Basic Info

  • chlorophyll arranged in groups by type of light absorbed
  • groups = photosystems
    • photosystems have multiple pigments that act as antennae to collect light and transmit it to the chlorophyll
    • 2 types that sit in grana modules

2. Exciting Electrons in Chlorophyll

  • electrons get energy boost from sunlight and jump to higher energy level
  • electrons can’t stay at that leevel w/o added energy so the fall back to original level (1 millionth of a second)
  • process is how glow sticks work
    • the chemical reaction boosts electrons to higher energy level
    • as the electrons fall back to normal level they give off light energy

3. First Photosystem (Water-Splitting Photosystem)

  • in first ps, electorn doesn’t fall back to chlorophyll
    • electron caught by another molecule: primary electron receptor
    • new electrons for chlorophyll come from splitting water
      • H goes to stroma
      • O is waste

4. Photosystem to Electron Acceptors

  • first photosystem sends electrons to the 2d photosystem via electron acceptors
  • after primary electron acceptor there are 3 electron acceptors in the grana membrane
    • as the electron and its energy is passed to each acceptor, the acceptor puts a H ion inside the grana
    • each handoff loses some of the electron’s energy

5. First Photosystem to Second Photosystem

  • the last electron acceptor transfers its electron and energy to the 2d photosystem
    • each time the electron is passed it loses a little energy
  • the 2d photosystem needs to be stimulated with light energy again to excite the electron high enough to be caught and useful
  • the electron then goes to another primary electron acceptor

6. Photosystem to NADPH

  • after the primary electron acceptor
    • the electron and a Hydrogen are transferred to NADP
    • NADP becomes NADPH

7. Hydrogens to ATP

  • each of the electron acceptors use the energy passing throu to put a Hydrogen ion into the grana
  • there is a buildup of H ions
  • the buildup can be used as energy to make ATP
    • ATP synthase is enzyme
    • hydrogens go from high concentration in grana to low concentration in stroma
      • works similar to waterfalls making electricity

B. Process 2: Light-INDEPENDENT Reactions
1. Basic Info

  • does NOT require light to occur, DOES require the products from the light dependent reactions
  • occurs in stroma or chloroplast
  • chloroplast uses energy stored in ATP and electrons in NADPH
    • get CO2 from air
    • forms new bonds between carbons and oxygen from carbon dioxide and hydrogens from water
    • process is called CALVIN CYCLE
    • product is actually G3P, can be used to make glucose or other products

C. Photosynthesis Summary
1. Basic summary of molecule

  • light provides energy to convert
    • ADP to ATP
    • NADP+ to NADPH
  • water is broken down and O released
  • ATP, NADPH and CO2 are then used in the light independent reactions to make G3P
  • G3P is used to make glucose

2. Overall Energy Transfer

  • energy from sun to electrons
  • energy from electrons to ATP and NADPH
  • energy from ATP and NADPH to glucose bonds
  • energy from glucose bonds used for organisms
  • all energy ultimately comes from sunlight

Clicker Questions
In which organelle does photosynthesis occur?
1.Cell wall
What would be an example of one of the antenna pigments?
How many times must the Calvin cycle turn for the plant to be able to produce a single
molecule of glucose?


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