Purpose of Photosynthesis: To convert light energy into chemical energy

Where does photosynthesis take place?
     Organism- Green Plants
    Organ- Mostly in the leaves        
    Organelle- Chloroplasts
                         Grana- (made up of stacks of flat sacs called thylakoids)--
                                    the light reaction occurs here
                                    Thylakoids contain chlorophyll.
                         Stroma- the liquid surrounding the grana-- the dark
                                    reaction occurs here
 
Light's role in photosynthesis:
    1. Light is made of photons that travel in waves
    2. The range of wavelengths of light that humans can see is called the Visible Spectrum
    3. The wavelengths in the Visible Spectrum are from 350nm to 750nm
    4. The colors in the Visible Spectrum are (ROYGBIV) red, orange, yellow, green,
        blue, indigo and violet.
    5. The shortest wavelength is violet (350nm) and the longest is red (750nm)
    6. The shorter wavelengths have the most energy.
    7. When light strikes an opaque object, the light is either reflected or absorbed.
    8. Light which is reflected, gives the object its color.
    9. Light which is absorbed, is usually converted to heat energy.
    10. Light which is absorbed by chlorophyll is converted to chemical energy during
        photosynthesis.
 
 
 

The Light Reaction- occurs in the grana      (Animation)
    I. The function of the light reaction is to capture the light energy
    II. The light reaction requires light.
    III. Summary of events:
        1. Water is split:  H₂O --> 2H + O₂   (oxygen is released into the air; H picked up by NADP⁺)
        _{2. ATP is made:  ADP + P -->  ATP}
        3. NADPH is made:  NADP⁺ + 2H --> NADPH
 
 

The Dark Reaction- (Calvin Cycle) occurs in the stroma
    I. The function of the dark reaction is to arrange the carbon chain using
        energy from the light reaction
    II. The dark reaction does not require light; it can occur in either light
          or darkness.
          However, a major limiting factor is presence of CO₂.
    II. Summary of events:
        1.Entering the Calvin Cycle:
            a. ATP and H from the light reaction
            b. 6CO₂ from the air
        2. CO₂ receptor is ribulose biphosphate (RuBP), the enzyme catalyzing this is rubisco
        3. Each CO₂ enters the cycle separately
        4. One glyceraldehyde 3-phosphate(G3P) (a 3-carbon sugar) is formed for every three
            CO₂ molecules that enters the cycle.
        5. Two molecules of G3P combine to form glucose.
 
 

Introduction to Photosynthesis-  check out this link for more details

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©1998 Linda Pellegrini. All rights reserved.