photosynthesis

• where does light dependant reaction take place?

  thylakoid membrane
• what are the reactants of the light dependant reaction

  water and light
• what are the products of the light dependant reaction?

  ATP and NADPH (Reduced nadp)
• Light dependent reaction - non cyclic phosphorylation

  1. Light energy absorbed by chlorophyll in photosystem II

  2. Excites electrons causing them to move down the electron transport chain

  3. Energy released from this causes water to split into protons, electrons and oxygen (this is called photolysis)

  4. Energy also used to transport protons into thylakoid membrane so it has a higher concentration of protons than stroma to create a proton gradient

  5. Protons move down gradient via ATP synthase, releasing energy for photophosphorylation

  6. Light energy also excites electrons in photosystem I, transferring them to NADP with a proton to form NADPH
• what is photophosphorylation


  process that combines ADP+pi to form ATP
• How are the thylakoid membrane adapted for function?

  • large SA
  • contain atp synthase channels
  • selectively permeable allowing a proton gradient
• GRANA


  stacks of flattened sacs (thylakoid)
• LAMELLAE


  Join thylakoids together
• STROMA


  fluid filled matrix
• What factor could inc the light dependant reaction

  inc light intensity
• CYCLIC PHOSPHORYLATION

  • only uses ps1 and only produces ATP
  • light energy excites electrons causing them to move down the electron transport chain providing energy to make ATP
  • electrons passed back into PSI via electron carriers meaning electrons are recycled and the process flows
• product of cyclic phopshorylation

  atp
• what does photolysis do?

  replaces electrons lost in pigment and uses protons for proton gradient
• where does light independent cycle take place?

  stroma
• what is needed for photosynthesis to take place?

  • CO2 and h20 supply
  • light energy
  • presence of photosynthetic pigments
  • suitable temperature
• STEPS IN LIGHT INDEPENDANT REACTION

  • CO2 enters leaf via diffusion and is combined with ruBP catalysed by rubisco
  • this produces 2x GP (3c)
  • ATP and NADPH from light dep. provides energy to turn GP into TP
  • TP then converted to glucose or back into Rubp
• 3 turns of the cycle produces how many molecules of tp?

  6
• optimum conditions for photosynthesis

  • high light intensity of certain wavelength
  • temp around 25 degrees as if too high then stomata will close and enzymes will denature
  • co2 level of 0.4 as storm will close if too high
• glucose/sugars synthesised used in respiration
• atp synthesised in condensation reaction of adp and pi used enzyme atp synthase
• what can you use to determine what pigments are in a leaf?

  TLC
• HOW TO DO TLC

  • grind up leaf and add anhydrous sodium sulphate and propanone
  • transfer liquid to tube and add petroleum ether and shake
  • 2 layers will form, transfer top layer into a diff test tube with anhydrous sodium sulfate
  • draw pencil line on TLC plate and add drop of solution onto it
  • put plate into container with prepared solvent so that solution is a bit above solvent
  • when solvent has almost reached top, remove and mark the solvent front
  • calc rf and repeat process for plant you comparing it against
• shady plants produce what pigments?

  dark red and purple
• what's a solvent front?

  furthest point the solvent has reached
• why should you investigate photosynthesis pigments in fume cupboard

  chemicals used are volatile and vapours are toxic
• a coloured solution absorbs more light than a colourless solution
• investigating DCPIP

  • cut leaves
  • use pestle and mortar to grind up leaf with chilled isolation solution
  • filter liquid into beaker through funnel lined with muslin cloth
  • centrifuge sample for 10mins at high speed to form a pellet
  • re suspend pellet in fresh chilled isolation sol. and store in ice for rest of experimnt
  • set up colorimeter with red filter and zero it using a cuvette containing chloroplast sol and distilled water
  • set up rack certain distance from lamp
  • add set vol chloroplast sol and dcpip &mix
  • immediately take sample of mix and add to clean cuvette and record absorbance in calorimeter
• how do you know if dehydrogenase activity is taking place?

  absorbance will decrease as DCPIP is reduced and loses blue colour
• the faster the rate dehydrogenase activity, the faster absorbance will decrease
• what can you use as a control when testing for dehydrogenase activity

  • 1 test tube containing only DCPIP and chilled isolation
  • 1 test tube contain dcpip and chloroplast extract but wrapped in tinfoil (prevent light)
  • no change in absorbance should occur between these two