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• Autotroph


  Organism that can produce complex organic compounds from simple inorganic substances, especially carbon dioxide, using energy from light or inorganic chemical reactions
• Heterotroph


  Organism that cannot produce its own food and instead obtains organic food substances by feeding on other organisms or their remains
• Photosynthetic pigment


  Pigment involved in photosynthesis
• Photosynthetic pigments have a role in photosynthesis
• Fundamental processes in photosynthesis


  1. Define

  2. Distinguish between light / 'dark' reactions

  3. Describe how photoautotrophs overcome CO2 limitations

  4. Describe the regulation of photosynthesis in relation to light, temperature and carbon dioxide
• Photosynthesis is the only biological process that can harvest energy from the sun
• Life on earth ultimately depends on energy derived from the sun
• Photosynthesis


  Converting light to chemical energy
• Photosynthesis reverses the direction of electron flow
• Water is split and electrons are transferred
• Hydrogen ions from water is transferred to carbon dioxide, reducing it to sugar
• Endergonic process


  Requires energy input
• Key components of the light reactions


  • Pigments
  • Photosystems
  • Electron transport chain
• Visible light


  Segment of the electromagnetic spectrum between 380 nm - 750 nm that is most important to life
• The atmosphere is selective and only allows visible light to pass through
• Photosynthetic pigments


  Absorb the light that powers photosynthesis
• Theodor W. Engelmann demonstrated in 1883 that light in the violet-blue and red portions of the spectrum is most effective for photosynthesis
• Chlorophyll a


  Green pigment found in plants, algae and cyanobacteria that absorbs light that powers photosynthesis through the excitation of electrons located in the porphyrin-like ring
• Chlorophyll b


  Has the same structure as chlorophyll a but the CH3 is replaced by an aldehyde group (-CHO) and absorbs at 500 - 640 nm (appearing olive green)
• Carotenoids


  Yellow, orange, red or brown pigments that absorb strongly in the blue-violet range and act as accessory pigments along with chlorophyll b
• Carotenoids provide photoprotection by preventing oxidative damage of chlorophyll during photosynthesis
• Photosynthetic pigments


  • Chlorophyll a
  • Chlorophyll b
  • Carotenoids
• Photosystem


  Where the light reactions of photosynthesis take place
• Possible fates of absorbed light energy


  1. Converting extra energy to heat or to a combination of heat and light

  2. Transferring energy to a neighbouring chlorophyll molecule - resonance energy transfer

  3. Transferring from a negative charged high-energy electron to another nearby molecule (electron acceptor)
• ATP


  Most important and versatile of the activated carriers in cells, a ribonucleotide where the terminal group is frequently split off by hydrolysis
• NADP+


  Closely related to NAD+ (nicotinamide adenine dinucleotide), picks up energy in the form of two-energy electrons plus a proton (H+)
• The electron transport chain

  1. Light energy drives the synthesis of both ATP and NADPH

  2. The oxygen evolving complex catalyzes the splitting of two water molecules (photolysis)

  3. The proton gradient drives the ATP synthase to generate ATP (photophosphorylation)
• 1. scheme


  The coupling of PSII and PSI that boosts electrons to the energy level needed to produce NADPH
• Cyclic electron flow


  1. To generate more ATP without making NADPH

  2. Switch photosystem I into cyclic mode also known as cyclic photophosphorylation
• Differences between non-cyclic and cyclic photophosphorylation


  • Photosystems involved
  • Is photolysis involved?
  • Fate of electrons
  • Products
• Light reactions


  • The splitting of water molecules (photolysis)
  • The production of oxygen
  • The excitation and transport of electrons
  • The generation of an electrochemical gradient
  • The production of NADPH and ATP
• The Calvin-Benson-Bassham cycle was awarded the Nobel Prize in Chemistry 1961 "for his research on the carbon dioxide assimilation in plants"
• The Calvin-Benson-Bassham cycle


  1. Regeneration

  2. Reduction

  3. Carboxylation

  4. Output
• RuBisCO is central to life on Earth
• Photorespiration


  Occurs when RuBisCO fixes oxygen instead of carbon dioxide, an energetically costly salvage pathway
• 75% of carbon is returned to the Calvin cycle in photorespiration, 15% is lost as CO2
• Carbon concentrating mechanisms


  • C4 plants
  • CAM plants
  • Algae
• C4 photosynthesis


  Shuttling CO2 via malate or aspartate from mesophyll cells to bundle sheath cells
• Crassulacean acid metabolism (CAM)


  Stomata in the leaves remain shut during the day, CO2 is stored as malic acid in the vacuole
• Blackman's law of limiting factors states that when a process is affected by more than one factor, its rate is limited by the factor which is nearest its minimum value