PHOTOSYNTHESIS

• Label the Diagram

  A) Outer Membrane

  B) Intermembrane Space

  C) Inner Membrane

  D) Stroma

  E) Granum

  F) Thylakoid

  G) Lamella

  H) Lumen

  
• Photolysis: The splitting of water into oxygen and hydrogen using light energy.
• Light dependent stage: Takes place between the lumen of the thylakoids. Electrons are excited by light energy and transferred to load the NADP+ coenzyme to become NADPH. Hydrogen Ions exit the Lumen through ATP Synthase, forming ATP. Water is split to replace missing electron in PSII, producing O2 and H ion.
• Where does the light-dependent stage occur?

  (Lumen of) Thylakoids
• Light Dependent stage

  Label the diagram

  A) Cytochrom

  B) Chlorophyll abosrbs light and excites and electron

  C) Electron Moves to cytochrome

  D) Electron moves to PSI, where it has lost its energy

  E) Chlorophyll absorbs light and re-energises electron

  F) Electron is picked up NADP+, forming NADPH

  G) Hydrolysis occurs when chlorophyll absorbs light energy

  H) Everytime the electron is moved, a H+ moves into lumen

  I) H+ exit via ATP synthase due to high concentration

  J) When H+ exits, ADP + Pi is combined to form ATP

  
• What are the inputs for the light dependent stage?

  H2O

  ADP+Pi

  NADP+
• What are the outputs of the Ligh-dependent stage?

  O2

  ATP

  NADPH
• Light Independant stage

  Glucose molecules are produced from CO2 in the Calvin Benson Cycle: Carbon Fixation, Reduction, and Regeneration.
• Carbon Fixation


  A CO2 molecule (1C) is fixed onto RuBP (5C) by using Rubisco, forming an unstable 6C molecule. This breaks down into two GP (3C) molecules.
• Reduction


  GP (3C) is reduced into GALP (3C) using NADPH and ATP. The now unloaded coenzyme go back to the light-dependent stage to be loaded again.
• Regeneration


  Some of the GALP molecules (3-C) become glucose (6C) through and intermediate process. The other GALP molecules are recombined to regenerate the RuBP in the first step, requiring ATP to do so.
• Inputs of the light-independent stage

  CO2

  NADPH

  ATP
• Outputs of the light-independent stage

  H2O

  NADP+

  ADP+Pi

  Glucose
• C3 Plants: Most plant species. Doesn't have any photosynthetic adaptations to reduce photorespiration.
• C4 Plants: The Calvin cycle and other processes are physically separated, with the reactions occurring in the mesophyll cells and the Calvin cycle occurring in bundle-sheath cells. Because the mesophyll cells constantly pump CO2  into neighbouring bundle-sheath cells in the form of malate, there’s always a high concentration of  CO2 relative to O2 right around rubisco. This strategy minimizes photorespiration.
• 1. Atmospheric CO2 is fixed in the mesophyll cells by PEP Carboxylase, forming oxaloacetate.
  2. Oxaloacetate is converted into malate, which can be transferred to the bundle sheath cells.
  3. In the bundle sheath cells, malate breaks down, releasing CO2.
  4. Rubisco fixates CO2 to RuBP as part of the calvin cycle.
  5. ATP is required to convert the 3C product of malate back into PEP

  
• C3 Plants are best adapted to cool or temperate climates. C4 plants are best adapted to hot climates. CAM plants are best adapted to arid, dry environments.
• CAM Plants: Open stomata at night when it’s cooler and less water loss occurs. During the day, they close their stomata to prevent water loss from transpiration. They use stored carbon dioxide (made through C4 pathways from the previous night, stored in the vacuoles) during the daytime to produce glucose through the Calvin Cycle.
• Photosynthesis Equation:

  light energy

  6CO2+12H2O ----------> C6H12O6+6O2+6H2O

  chlorophyll
• Carbon Dioxide levels:

  As Co2 concentration increases, rate of photosynthesis increases. Highest rate can be reached generally at 0.1%
• Temperature:

  Rate of Photosynthesis increases as temperature increases as increased molecular collisions occur.

  At high temperatures, Rubisco has an increased affinity for oxygen rather than carbon, increasing rate of photorespiration and decreasing rate of photosynthesis.
• Photosynthetic Autotrophs: synthesise their carbon compounds from inorganic materials using light as the energy source to do so.
• Water availability

  Water is an input, so low levels means low rate of PS

  If plant loses too much water, stomata will become flaccid and close, reducing amount of Co2 entering the plant, therefore decreasing rate of PS.
• Limiting factors

  A factor that is holding back the rate of PS.

  I.e. when light availability is at optimal level, but rate of PS is still low, limiting factors may include low Co2 concentration.