BukhariH/4.3.1 Photosynthesis Pigments.md

f) define the term photosynthetic pigment;

• Photosynthetic pigments are molecules that absorb light energy.
• Each pigment absorbs a specific wavelength of light in the visible light region
• Each pigment also has specific peak of absorption
• Wavelengths outside the range a reflected
• This reflected light is the colour which they appear to us as

g) explain the importance of photosynthetic pigments in photosynthesis;

• Photosynthetic Pigments are held in place by proteins in the thylakoid membranes
• They are arranged in a funnel shape structure called a photosystem
• There are two type of pigments:
  • Primary Pigments
    • Structure:
      • Consist of a long phytol chain and porphyrin group
        • The porphrin group is similar to the haem group but contains Magnesium instead of Iron
    • Light hitting the chlorophyll causes a pair of electrons belonging to Magnesium to become excited
    • Primary pigments are Chlorophyll a and Chlorophyll b
      • Chlorophyll a has two forms - P680 and P700
        • They both appear yellow-green
        • Each absorb red light at slightly different wavelengths
        • Both also absorb blue light around the wavelength of 450 nm
        • Both are found in the Primary Pigment Reaction Centre
        • P680 is found in photosystem I
        • P700 is found in photosystem II
      • Chlorophyll b absorbs light around wavelength of 500 nm and 640 nm
        • it appears blue-green
  • Accessory Pigments
    • They absorb wavelengths that chlorophyll doesn't absorb well and pass the energy down to chlorophyll
    • Carotenoid absorb blue light and reflect yellow and orange light
    • Not directly involved in the light dependent reaction
    • Do not contain the porphyrin (magnesium) group
    • Carotene (orange) and xanthophyll (yellow) are the main carotenoid pigments