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Photosynthesis (Factors affecting photosynthesis (Light (Light intensity…

- - - - Slowest reaction
      - Factor which is nearest min. value
  - - - Low; Rate of photo. (ROP) increases linearly
      - No longer limiting --> light saturated
      - Not normally the major limiting factor
      - Very high: may damage chlorophyll, decrease ROP
        
        Plants naturally exposed to such conditions usually protected by thick cuticles and hairy leaves
    - - Compensation pt is the pt at which ROP is equal to rate of respiration (ROr)
      - All CO2 produced during respiration used for photosynthesis
      - All O2 produced used for respiration
      - No net gaseous exchange between plant and environment
      - Reached at low light intensities
    - - Shade plants
        
        lower ROr
        
        Thin with fewer palisade mesophyll layers
        
        Has fewer cells--> less energy for maintenance
        
        Reach compensation point at lower light intensity & faster
      - Sun plants
        
        Higher ROr & ROP
        
        Thick, more palisade mesophyll layers
        
        Trap more light energy for prodn of carbohydrates
        
        More cells--> more energy for maintenance
        
        Absorb @ higher light intensities
    - - Wavelength inversely proportional to energy possessed by light
        
        Blue light more energy than red
  - - - Mol. move more rapidly, greater chance of colliding
  - - - Diseases, mineral deficiency, normal ageing process, lack of light
    - - Chlorotic
        
        chlorosis
  - - - Short circuits non- cyclic e flow in chloroplast--> inhibits LDR
    - - Disrupts bond interactions between R groups of proteins in ETC
  - - - Close stomata, prevent access of CO2 for photosunthesis
      - Abscisic acid, growth inhibitor, accumulates in H2O deficient leaves of some specieis
  - - - Oxygen competes with CO2 with Rubisco, which combines CO2 with RuBP during LIR
      - O2 high [ ] compared to CO2
      - ATP used instead of being produced
- - - - Outer: selectively permeable
      - Inner: Highly permeable, transporters for substance
  - - - Circular DNA, 70S ribosomes, starch granules, oil droplets and enzymes in CC
  - - - Thylakoid lumen: Compartmentalisation allows chemiosmosis, ATP to be produced by photophosphorylation
  - - - Increase SA, amt of pigments for LDR
    - - Connect thylakoid compartments into single, continuous compartment within stroma
- - - - Chlorophyll embedded in thylakoid membrane
  - - - Chlorophyll a
        
        Major pigment; absorbs red and blue light
        
        Other pigments absorb light and transfer energy to ca of the reaction centre (accessory pigments), initiate LDR
        
        chlorophyll b
- - - - Some energy used to make ATP
  - - - NAD
      - NADP
      - FAD
- - - - Carotenoids peak at slightly higher wavelengrh than ca cb
    - - Absorb intermediate wavelengths of light, broadening spectrum of colours driving photosynthesis
        
        not very effective; transfer only 10% energy
    - - Absorb excessive light, prevent auto-oxidation of chlorophyll
        
        Prevents photobleaching
- - - - Resonance energy transfer
  - - - Synthesise NADPH and ATP using light energy from light harvesting stage
      - Chemical energy trapped in ATP and NADPH
      - NADPH and ATP used in light- dependent rxn to fix C02, trapped in glucose
    - - Both PSII & PSI, ATP & NADPH produced
      - Steps
        
        Photon of light strikes pigment mol in a LHC, energy relayed via resonance energy transfer until it reaches 1 of 2 special ca mol in PSII rxn centre --> excites P680 to higher energy state
        
        P680 captured by primary e acceptor in rxn centre, missing e now
        
        Photolysis of water
        
        Enzymes splits water mol into 2 e, 2 H ions and O atom--> e released replenish deficit of e from rxn centre PSII; O2 released
        
        Energised e passes from PSII to PSI via 1st ETC: Pq> cytochrome (b-f) complex > Pc . Increasing e affinity--> transport of e down ETC unidirectional
        
        Free energy released from exergonic reaction used to pump protons against conc gradient from stroma to thylakoid space--> proton gradient > ATP synthesis, photophosphorylation
        
        Same steps as 1, except now in PSI, P700, e deficit replenished by e from PSII
        
        Excited e --> Fd (2nd ETC)
        
        Enzyme NADP reductase transfers e from Fd to NADP --> 2 E for reduction to NADPH
    - - PI, NO NADPH
      - Light absorbed by LHC passed on to ca in rxn centre PSI
      - P700 mol emit energised e, raised to higher energy level, picked up by primary e acceptor
      - Energised e from PSI passed to Fd, cycled back to cytochrome (b-f) complex and Pc
      - Energy released synthesis ATP from ADP and Pi-->ATP
    - - Mechanism of ATP prod
      - Thylakoid impermeable to H+> accumulation of H + during light rxn
      - e flow from PSII to PSI--> free energy--> cytochrome complex pumps H+ against conc gradient from stroma into thylakoid space
      - Photolysis of water produces H+
      - Proton gradient
        
        synthesis of ATP through ATP synthase complex
        
        H+ diffuse down gradient from thylakoid space across thylakoid membrane into stroma through ATP synthase complex
  - - - CO2 combines with RuBP to form unstable 6C intermediate--> enzyme Rubisco
        
        Unstable 6C Breaks down into 2 mols of GP
    - - GP phosphorylated by ATP--> 1,3 BPG
        
        Pair of e from NADPH reduced BPG to TP
    - - 3 CO2--> 3 RuBP and 6 mol of TP formed
        
        TP
        
        5 TP used to regenerate 3 mol of RuBP --> 3 more ATP invested
    - - 2 mol of TP--> 1 mol of hexose sugar
        
        1 mol of hexose sugar needs 6 turns of calvin cycle
- - - - Light energy captured using a mixture of pigments including chlorophyll
    - - Light energy harnessed, excite and displace e from chlorophyll
      - Light energy converted to chemical energy through a flow of e that is coupled to ATP synthesis
      - NADPH produced
      - Photolysis of water
  - - - Chemical energy of ATP and NADPH used in reduction of C--> manufacture of sugars
- - - - A pair of special ca molecules which act as a irreversible trap for energy
- - - - TP converted to hexose sugars, esp glucose and fructose--> respiratory substrates for ATP prod
      - Glucose mol covalently linked together, stored as starch granules
      - Glucose mol. polymerised to form cellulose ; needed for structural growth of plants
    - - GP converted o acetyl group --> added to coenzyme a to from acetyl CoA
        
        Converted to fatty acids in cytoplasm and chloroplasts
      - Glycerol from TP
        
        Fatty acids and glycerol --> triglycerides & phospholipids
    - - GP an TP precursors of aa
      - nitrogen incorporated into product mol
        
        Plants use these mol to make nitrogen- containing compounds, including nuclotides for DNA and RNA synthesis
- - - - Trnaferring energy directly to neighbouring chlorophyll mol.
    - - e returns to orignal state by taking up a low-energy e from electron donor (water)