photosynthesis

• the formula for photosynthesis is 6CO2+ 6H2O ----> C6 H12 O6 + 6O2
• photosynthesis is a 2 step biochemical process which takes place in the chloroplast
• light dependent reactions take place in the phospholipid bilayer of the thylakoid membrane, inside the chloroplast
• light independent reactions are the reactions that occur in the stroma of the chloroplast
• in photosynthesis NADP, ADP, Pi and water are needed for the light dependent reaction
• chlorophyll is the light absorbing pigment which is embedded in phospholipid bilayers
• chlorophyll best absorbs blue and red wavelengths of light
• What initiates the light dependent reactions in photosynthesis?

  Light of the correct wavelength strikes chlorophyll
• What happens to electrons when light strikes chlorophyll during the light dependent reactions?

  Electrons are excited and leave the chlorophyll molecule, a process known as photoionisation
• What is the term used for the process when electrons leave the chlorophyll molecule?

  Photoionisation
• What occurs after the electron is accepted by an electron carrier?

  The electron carrier is reduced
• How are electrons transferred during the light dependent reactions?

  Electrons are passed down a series of electron carriers through redox reactions
• What is the significance of the energy released during the transfer of electrons between carriers?

  The energy is used to move H+ ions from the stroma to the thylakoid space against their concentration gradient
• What happens to H+ ions during the light dependent reactions?

  H+ ions are moved from the stroma to the thylakoid space
• What happens when light strikes another chlorophyll molecule during the light dependent reactions?

  Electrons are passed down a second series of electron carriers
• What is the final acceptor of electrons and H+ ions in the light dependent reactions?

  NADP
• What is produced when NADP accepts electrons and H+ ions?

  NADPH
• the photolysis of water produces H+ ions, electrons which replace those lost from the chlorophyll, oxygen is the waste product and diffuses out of the chloroplast
• the process of light independent reactions (Clavin cycle):

  1.) RUBP combines with CO2

  2.) enzyme rubisco catalyses the reaction 

  3.) produces 2X molecules of GP

  4.) GP is reduced to triose phosphate 

  5.) using energy from ATP

  6.) also requires NADPH (reduced NADP) 

  7.) triose 2x phosphate converted back to RUBP

  8.) using energy from atp 

  9.) also produces 1/6th  of a glucose molecule 
• law of limiting factors refers to when a factor influencing photosynthesis is in short supply and this limits the rate
• the main limiting factors for photosynthesis are light intensity, water availability, CO2 concentration and temperature
• if light intensity is the limiting factor in photosynthesis this means that the light dependent reactions are effected and cannot produce the ATP and NADPH needed for the light independent reactions
• if carbon dioxide is the limiting factor in photosynthesis this means the light independent reactions are effected, Rubisco cannot convert RUBP to GP without co2 meaning there is a fall in levels of triose phosphate produced and the rate of photosynthesis is decreased
• if water availability is the limiting factor in photosynthesis this means the light dependent reactions are effected, there is a lack of electrons and h+ from the photolysis of water so the production of ATP and NADPH are disrupted
• the light dependent reactions take place in the thylakoid membranes in chloroplasts
• the light independent reactions take place in the stroma of the chlorophyll
• the role of light in photoionisation is to excite electrons and raise them to a higher energy level allowing them to be released from the chlorophyll molecule
• the 2 main stages involved in ATP production in the light dependent reactions are energy from electron transport chains and chemiosmosis
• how is a concentration gradient created during chemiosmosis?

  energy released from the electron transport chain is used to transport H+ ions from the stroma into the thylakoid space
• how does chemiosmosis produce ATP in the LDR?

  H+ ions move down their concentration gradient from the thylakoid space to the stroma via the channel protein ATP synthase - catalysing the reaction of ADP and Pi to ATP
• 3 main stages of the Calvin cycle:

  • fixation
  • reduction
  • regeneration
• the purpose of chromatography is to separate plant pigments based on their solubility in the solvent
• how can chromatography be used to separate photosynthetic pigments?

  1.) Use a capillary tube to spot pigment extract onto pencil 'start line' (origin) 1 cm above bottom of paper.

  2.) Place chromatography paper in solvent. (origin should be above solvent level).

  3)Allow solvent to run until it almost touches the other end of the paper. Pigments move different distances.
• why would a decreased temperature decrease the rate of the light independent reaction?

  enzymes are involved in the reactions. so if the temperature lowers, there is less kinetic energy and less collisions between enzyme and substrate
• why is it important that plants produce ATP via respiration as well as photosynthesis?

  • in the dark no ATP can be produced via photosynthesis 
  • some tissues cannot photosynthesise 
  • ATP cannot be stored 
  • plants use more ATP than they produce in photosynthesis 
  • ATP is used for active transport