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photosynthesis (photosynthesis and respiration (photosynthesis occurs in…

- - - - light dependant stage occurs in grana
      - thylakoids in different grana are connected via intergranal lamellae
      - lots or grana and many chloroplasts there is a large surface area for distribution of photosystems which contain photosynthetic pigments that trap sunlight and electron carriers and ATP synthase enzymes need to convert light energy to ATP
      - proteins in thylakoid membranes hold photosystems in place
      - grana is surrounded by stroma so products of light dependant can be used in light independent
    - - contains enzymes needed to catalyse light independent reactions
      - contains starch grains, fat droplets, small ribosomes and dna
      - loop of dna contains code for proteins needed for photosynthesis which are assembled at ribosomes
    - - photosystems contain photosynthetic pigments
      - each pigment absorbs a specific wavelength of light and thus appears the colour of the wavelengths its reflecting
      - the energy is transferred from accessory pigments to primary pigments in reaction centre
      - chlorophylls
        
        structure= porphyrin ring containing a magnesium atom and a long hydrocarbon chain
        
        chlorophyll a= appear blue/green, and absorb red light, p680 in PSII, p700 in PSI, also absorbs some blue light at 440nm
        
        chlorophyl b= absorbs light of wavelengths 400-500nm, reflect yellow and orange light, appears yellow green
      - accessory pigments
        
        carotenoids= absorb blue light of wavelengths 400-500nm and reflect orange/ yellow light
        
        xanthophyll absorb blue and green light at wavelengths 375-550 and reflect yellow light
- - - - takes place in thylakoid membrane
      - light energy is absorbed by photosynthetic pigments in photosystems and are converted to chemical energy
      - the light energy is used to add a phosphate group to ADP to form ATP and to reduce NADP to NADPH (reduced NADP- transfers hydrogen and electrons to other molecules so is energy rich)
      - H2O is oxidised to O2
      - ATP transfers energy, NADPH transfers hydrogen
    - - (calvin cycle)
      - occurs in stroma
      - ATP and NADPH supply the energy and hydrogen to make glucose from CO2
  - - - light energy absorbed by PSII and transported to primary pigment reaction centre
      - light energy excites electrons in chlorophyll
      - the electrons move to a higher energy level
      - these electrons are captured by electron carrier (protein with iron centre) in thylakoid membrane and move along electron transport chain to PSI
    - - as the excited electrons leave PSII to move along electron transport chain they must be replaced
      - light energy splits water into photons, electrons and oxygen
      - 2H2O---> 4H+ + 4e- + O2
    - - the excited electrons lose energy as they move along the electron transport chain
      - this energy is used to transport H+ into the thylakoid via membrane proteins called protein pumps so the thylakoid has a HIGHER CONCENTRATION of protons than the stroma forming a proton gradient
      - protons move down the conc gradient into stroma via ATP synthase enzyme. the energy from this movement combines ADP with an inorganic phosphate to form ATP
      - when iron ion combines with electron it becomes reduced (Fe2+) when it donates electron to next carrier protein it becomes deoxidised (Fe3+)
    - - light energy absorbed by PSI excites electrons to move to an even higher energy level
      - finally the electrons are accepted by ferredoxin and transferred to NADP along with a H+ in the stroma to form NADPH
      - NADP reduction is catalysed by NADP reductase
- - - - CO2 enters leaf via stomata and diffuses into chloroplast stroma
      - its combined with RuBP which produces an unstable 6 carbon intermediate compound which breaks down into 2 molecules of GP (3 carbon compounds)
      - RuBisCO catalyzes the reaction
    - - ATP (produced from light dependant reaction) provides energy to turn GP into TP
      - this reaction also required H+ ions which comes from NADPH which is then recycled to NADP and used in LD reaction again
      - TP is converted into useful organic compounds e.g. glucose, carbohydrates, lipids, amino acids