photosynthesis - occurs in bacteria, algae, stems/leaves of plants 

• Jan Baptista van Helmont - showed that soil didn't add mass to plants; believed that water provided the extra mass
• Joseph Priestly - found that living vegetation restores oxygen into the air
• Jan Ingenhousz - found that plants' green leaves (not roots) only restore air in presence of sunlight
• chloroplasts - organelles that carry out photosynthesis
  • mesophyll - thick layer of cells rich in chloroplasts
  • thylakoids - internal chloroplast membranes
  • grana - stacks of thylakoids
  • stroma - semi-liquid substance that holds enzymes needed to synthesize organic molecules
• light-dependent reactions - capturing energy from sunlight, using energy to make ATP/NADPH
  • takes place on thylakoid membrane
• Calvin cycle (light-independent reaction) - carbon fixation
  • synthesizes organic molecules from CO2 in air and energy in ATP/NADPH
  • doesn't need light to work
  • takes place in stroma
• photosystem - clusters of photosynthetic pigments in thylakoids
  • each pigment can capture photons (energy packets)
  • energy of excited electrons move from chlorophyll molecule to chlorophyll molecule
  • ATP/NADPH generation starts as energy reaches membrane-bound protein

F. F. Blackman - proposed that photosynthesis is comprised of multiple steps 

• found that first part of photosynthesis required light
• dark reactions limited by CO2, not directly involved w/ light
• temperature increased dark reactions up until 35°C, where it would start to denature proteins
• enzymes involved in dark reactions

C. B. van Niel - discovered roles of light/dark reactions 

• discovered that O2 produced came from H2O, not CO2
• NADPH and ATP formed in light reactions are used in Calvin cycle to form simple sugars from CO2
• carbon fixation - process where reducing power from splitting of water is used to convert CO2 to organic matter
• high energy electrons form the C-H bonds of new organic molecules
• lack of CO2 leads to accumulation of ATP

biophysics of light - contains units of energy called photons 

• photoelectric effect - photons transfer energy to electrons, facilitating passage of electricity
• short-wavelength light has higher energy than long-wavelength light
• gamma rays - shortest wavelength, highest energy
• radio waves - longest wavelength, lowest energy
• violet - shortest wavelength in visible light
• red - longest wavelength in visible light
• UV light - has more energy, shorter wavelength than visible light
  • important source of energy for early life
  • can cause mutations by messing up DNA bonds
• photon energy either lost as heat or absorbed by electrons when photons strike something
• absorption spectrum - range/efficiency of photons a substance can absorb

pigments - good absorbers of light  

• chlorophyll - absorbs violet-blue/red light; reflects green light
• chlorophyll a - main photosynthetic pigment; only pigment that can directly convert light to chemical energy
• chlorophyll b - secondary light-absorbing pigment; can absorb wavelengths that chlorophyll alpha can’t
• carotenoids - absorbs wavelengths not efficiently absorbed by chlorophyll