photosynthesis

• what wavelength of light do both photosystems absorb

  • PS11 : 700nm
  • PS1 : 680nm
• describe the process of non-cyclic phosphorylation

  • light absorbed at PS11 excites electrons at the reaction centres
  • electrons move across ETC (cytochromes)
  • ATP made from chemiosmosis
  • e- lost at PS11 are replaced by ones from photolysis and e- lost at PS1 are replaced by ones from PS11
  • NADP accept e- and H+ to form NADPH
• describe the process of cyclic phosphorylation

  • some e- that are released from the PS1 ETC are not picked up by NADP
  • and are recycled to PS1
  • so more energy can be produced through chemiosmosis
  • results in ATP but not NADPH
• define photolysis

  • the splitting of water into O2 , H+ and e- using light energy absorbed by chlorophyll
  • catalysed by the oxygen evolving complex which forms part of PS11
• describe the process of chemiosmosis

  • excited e- move along ETC
  • energy used to pump H+ from stroma into thylakoid lumen
  • electrochemical gradient set up
  • H+ pass through ATP synthase using proton motive force
• how is RuBP regenerated (3)

  • for 1 glucose molecule 6 Co2 are required
  • the Calvin cycle turns 6x and 12 3C TP molecules are produced
  • 2/12 TP molecules are used to make glucose
  • leaving 30 carbons / 5 = 6 RuBP
• summarise the Calvin cycle into three steps

  • carbon fixation
  • reduction of GP -> TP
  • regeneration of RuBP
• why at higher light intensities the rate of photosynthesis would still plateau ?

  • other factor (temperature or CO2 concentration) becomes limiting factor
  • Calvin cycle is dependant on temperature because it is enzyme controlled
  • Carbon fixation is dependant on CO2 concentration
• name two polysaccharides that can be synthesised from TP

  • starch
  • cellulose
• define autotroph and heterotroph

  • makes organic molecules from CO2
  • obtains organic molecules from digesting organic molecules / organisms
• describe how light is harvested in the chloroplast membranes

  • primary (chlorophyll A ) and accessory (chlorophyll B , carotenoids and xanthophylls ) form an antenna complex
  • photons absorbed by pigment and provides energy to excite e-
  • energy/photons passed from pigment to pigment until reaction centre with chlorophyll a is reached
  • range or pigments means range of wavelengths can be absorbed
• how would a weedkiller binding to electrons in PS1 result in the death of a plant

  • stops non cyclic photophosphorylation
  • no e- available to form NADPH
  • ATP still produced from cyclic photophosphorylation
  • no NADPH and less ATP available for Calvin cycle