Photosynthetic Pigments

• Light wavelengths not absorbed but are reflected or transmitted (these are colours we see), mostly chlorophyll a and chlorophyll b, but there are also carotenoids (β-carotene) and xanthophylls
• Photosynthetic pigments are coloured compounds in thylakoid membranes which absorb light energy, there are many different pigments and each absorbs a distinct range of light wavelength, with absorption peaks at certain wavelengths
• Photosynthetic Pigments

  A) 700

  B) 680

  C) 700

  D) 680

  E) I

  F) II

  G) Blue-green

  H) I + II

  I) 420-430

  J) blue-violet

  K) 670

  L) red

  M) Hydrophobic

  N) thylakoid

  O) Hydrophilic

  P) porphyrin

  Q) magnesium

  R) Yellow-green

  S) 460

  T) blue

  U) 650

  V) red-orange

  W) Red

  X) orange

  Y) yellow

  Z) brown

  [) 450-510

  \) UV

  ]) mutagenic

  ^) hydrocarbon rings

  _) hydrocarbon chains

  `) porphyrin

  
• Photosystems

  • Photosynthetic pigments cluster in a funnel-shape embedded in thylakoid membrane; each photosystem has one primary pigment molecule (chlorophyll a) at reaction centre and many accessory pigments (200+)
  • Protein molecules support pigments in optimal energy transfer positions and hold their position in two types: Photosystem 1 (PSI or P700) and Photosystem 2 (PSII or P680)
• • Absorption spectrum: Graph shows light absorption by pigments at wavelengths: Quote wavelength at maximum absorption, indicate wavelengths with higher absorption peak if multiple peaks exist and quote range where absorption is lowest

  A) chlorophyll a

  B) chlorophyll b

  C) carotenoid

  
• Action spectrum: Graph showing rate of photosynthesis at different visible light wavelengths; spectra shapes are very similar, indicating photosynthetic pigments absorb wavelengths of light used in photosynthesis