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
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