LEC: photosynthesis

• Photosynthesis

  the process that converts solar energy into chemical energy

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

  
  

  - endergonic reaction: puts energy in

  - anabolic reaction: BUILDS sugar
• Autotrophs

  sustain themselves without eating anything dervied from other organisms
• Photoautotrophs

  use the energy of the sunlight to make organic molecules from H2O and CO2
• Chlorophyll

  the green pigment within chloroplasts - on the thylakoid membrane

  
  

  - light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast
• Chloroplast


  membrane-bound organelle found in plant cells
• Stomata


  microscopic pores in a leaf where CO2 enters and O2 exits

  
  

  "mouth" "where the leaf breaths"
• Mesophyll


  cells of a leaf that contain chloroplasts

  
  

  - contain most of the chloroplasts of a leaf

  - found in interior tissue of a leaf
• Thylakoids

  membrane stacks found within the chlorplast

  
  

  - stacked in columns (grana)

  - chlorophyll is found in the membrane of the thylakoids

  - where light reaction occurs (on the membranes)
• Stroma


  a dense fluid within a chlorplast

  
  

  - where synthesis occurs (calvin cycle)

  - surrounds the thylakoids
• Water in Photosynthesis

  water = source of electrond, oxygen is a by-product

  - chlorplasts split water into hydrogen and oxygen, incorporating the ELECTRONS of hydrogen into the sugar molecule
• The Light Reaction

  - split water

  - release oxygen

  - reduce NADP+ to NADPH (electron carrier)

  - generate ATP

  
  

  takes place in the thylakoids
• Calvin Cycle


  forms sugar from CO2 using ATP and NADPH

  - carbon fixation

  - reduction (sugar is made)

  - regeneration of the CO2 acceptor (RuBP)

  
  

  "dark reaction", takes place in the stroma
• Wavelength


  the distance between crests of waves

  
  

  - determines the type of electromagnetic energy and how powerful that energy is

  smaller wavelength = higher energy = more powerful

  larger wavelengh = lower energy = less powerful
• Electromagnetic Energy


  (electromagnetic radiation) travels in rythmic waves

  
  

  light is a form of electromagnetic energy (photon: particle that constitutes the light)
• Electromagnetic Spectrum


  the entire range of electromagnetic energy
• Visible Light Spectrum


  wavelengths that produce colors we can see
• Pigments

  substance that absorbs visible light

  
  

  - molecule that reacts with light

  - different pigments absorb different wavelengths and reflect/transmit others

  ex: leaves appear green because chlorophyll reflects and transmits green light, every other color is absorbed
• Common Pigments

  chlorpophyll a, chlorophyll b, carotenoids
• Chlorophyll a


  main photosynthetic pigment
• Chlorophyll b

  broaden the spectrum for photosynthesis
• Carotenoids


  absorb excess light that would damage chlorophyll
• Apsorption Spectrum

  a graph plotting a pigments light absorption versus wavelength
• Action Spectrum


  profiles the relative effectivenes of different wavelengths of different radiations in a driving process
• Photosystems

  consists of a reaction-center complex (type of protein complex) and is surrounded by a light-harvesting complex

  - photosystem II and photosystem I
• Photosystem II


  (PS II) functions first, is the best at absorbing wavelength of 680nm (P680)
• Photosystem I


  (PS I) functions second, best at absorbing a wavelength of 700 (P700)
• Primary Electron Acceptor

  in the reaction-center, takes the excited electron

  
  

  - holds the excited electrons (in excied state: when pigments absorb light)
• Linear Electron Flow

  primary pathway, produces ATP and NADPH - O2 is a by-product

  PS II first, then PS I second

  - light excites electron

  - electron transfered to primary electron acceptor

  - electron falls down electron transport chain

  - passed to the next
• Cyclic Electron Flow

  only uses photosystem I and produces ATP, not NADPH

  - reuses electrons

  - protects cells from light damage

  - prevents build up of oxygen
• Rubisco


  (RuBP) enzyme that takes CO2 for carbon fixation
• Photorespiration

  rubisco adds O2 to the CalvinCycle due to the lack of CO2 (closed stomata)

  - uses up excess oxygen (useful)

  - consumes O2 and burns off organic fuel (wasteful)

  
  

  - limits damaging products of light reaction that build up in the absence of the calvin cycle
• C3 Plant


  most plants, initial fixation of CO2 using rubisco to make three-carbon compound (G3P)
• C4 Plant


  minimixe the cost of photorespiration by incorperatinfincorporating CO2 in four-carbon compounds in mesophyll cells

  
  

  - requires enzyme, PEP Carboxylateminimize
• PEP Carboxylate


  used by C4 plants

  - only grabs CO2 and gives it to rubisco

  - will grab CO2 for fixation even when levels are low

  - will grab CO2 until it is all used up
• CAM Plant

  Crassulacean acid metabolism: stores carbon dioxide at night, releases it during the day

  
  

  - open stomata at night (less heat = less water loss)

  - close stomata during the day

  - increasing the efficiency of photosynthesis