photosynthesis

• light dependant stage

  1. light is absorbed by chlorophyll
  2. this excites electrons
  3. electrons are passed along Electron Transport Chain
  4. energy is used to generate ATP and split water into hydrogen and oxygen
  5. oxygen is evolved and NADP picks up H to make NADPH
• light energy can be

  • absorbed to generate ATP for photolysis
  • reflected
  • transmitted (goes straight through the leaf)
• Each photosynthetic pigment absorbs different wavelengths of light. The absorption spectra shows the wavelength of light that each pigment absorbs.

  
• chlorophyll absorbs

  mostly blue and red light
• xanthophyll, carotene and chlorophyll b absorb

  other wavelengths of light. the energy that they capture is passed onto chlorophyll A
• carotenoid pigments is an advantage as

  extends the range of wavelength of light that the plant can absorb and they pass energy to chlorophyll for photosynthesis
• carbon fixation (the calvin cycle)

  1. carbon dioxide enters the cycle and becomes attached to the RuBP
  2. the carbon dioxide and RuBP combine to make 3PG using RuBisCO
  3. the 3PG then joins with the hydrogen from NADPH and is phosphorylated by the addition of phosphate from ATP which supplies the energy
  4. this process produces G3P
  5. some G3P is then used to regenerate RUBP. the remainder is used to synthesise sugars
• • sugars
  • used in respiration as an energy source
  • built into cellulose for structural use
  • built into starch providing energy store
  • other biosynthetic pathways