CH 8 Lecture Notes
 Photosynthesis: Process that converts Solar E to chemical E
 Provides fuel for entire living world
 Made by plants algae and some prokaryotic organisms
Autotroph don’t consume anything derived from other organisms
 Are the producers  make organic molecules from inorganic molecules, CO2 and
sunlight
 Photoautotrophs or chemoautotrophs
Heterotroph consumers, depend on autotrophs for fuel and O2
Structure: chloroplasts are membrane bound enzymes and molecules
 Makes photosynthesis efficient (remember SA)
 Descended from bacteria (remember endosymbiosis)
 CO2 enters and O2 exits via stomata (microscopic pores)
 Photosynthesis occurs in leaves (mesophyll—interior tissue)
 Chloroplasts: Are green from chlorophyll (pigment), found in thylakoids (stacked in
grana)
 Chloroplasts split H2O into H+ and O and uses e- to create sugar mol. Releases O2 as a by
product
Electron flow is opposite of cell resp. Redox Rxn  H2O is oxidized, CO2 is reduced.
 Endergonic Rxn: energy produced from sunlight
Process: 2 steps
 Light Rxns (photo): Splits H2O, releases O2, Reduces NADP+ to NADPH, generates ATP
through photophosphorylation
 Calvin cycle (synthesis):First carbon is fixed (CO2 incorporated into organic molecules.
Forms sugar from CO2 using ATP and NADH
Light Rxns: chloroplasts are solar powered chemical factories.
 Thylakoids transform light energy to chemical Energy in ATP and NADPH
Light: electromagnetic E, or radiation. Travels in waves
 Wavelength= distance between crests of waves, determines type of energy
 Electromagnetic spectrum entire range of wavelengths, or E
 Also acts as a particle  photon
Visible light: wavelengths that produce colors that we can see
Pigment: substances that absorb visible light
 wavelengths that are not absorbed are reflected/transmitted
 Leaves are green because chlorophyll reflects/transmits green light
 Spectrophotometer: measures pigments ability to absorb wavelengths
 Absorption spectrum: Graph that plots pigment’s light absorption vs. wavelength
 Chlorophyll α (primary chlorophyll) works best with Violet-blue and Red light
 Caroteniods: absorb otherwise harmful light waves
 Chlorophyll B (and others) absorb slightly different wavelengths, extend types of light
that will work for photosynthesis  Accessory Pigments
 Pigments absorb light moves from ground to excited state (unstable)
o Fall back down releases photon (fluorescence light and heat
Photosystems: 2 components
 1. light harvesting complex which transfer E of photons to the Rxn center complex
 2. rxn-center complex (protein complex) : Houses the primary e- acceptor (PEA) which
accepts e- from chlorophyll (and is reduced)  Frist step of light Rxn
Two photosystems: PS II and PS I. Linear flow of electrons:
1. Photon hits pigment and is passed from pigment to pigment in the light-harvesting
complex
2. Excited e- transferred to the PEA from final pigment (P680)becomes P680+
3. H2O is split into H+, O and e- by an enzyme and the e- are transferred to P680+. O2
released
4. e- falls down ETC from PS II PEA to PS I
5. E released in ETC creates a proton gradient: diffusion of H+ across membrane drives ATP
synthesis
6. In PS I (like PS II), transferred light energy excites P700, lose an e - to PEA, becomes
P700+
7. P700+ accepts e- from PS II via the ETC to become P700 again
8. Excited electrons “fall” down an ETC from PEA of PS I to the protein ferredoxin (Fd)
9. The e- are transferred to NADP, reducing it to NADPH, and become available for the
reactions of the Calvin cycle
10. This process also removes an H from the stroma
Calvin Cycle: Chem E of ATP and NADH reduced CO2 to sugar
 Like Krebs cycle, regenerates its starting materials, BUT is anabolic
 Build sugar out of smaller molecules using ATP and reducing power of e Carbon enters as CO2, leaves as glyceraldehyde 3-phosphate (G3P)
 Net synthesis of 1 G3P= 3 cycles (3 CO2 needed)
3 phases:
1. Carbon fixation: CO2 incorporated into RuBP using Rubisco (Enzyme)
2. Reduction: G3P produced using RuBP, ATP and NADPH
3. Regeneration: other G3P rearranged to regenerate RUBP (initial CO2 receptor)