Chapter 6 Photosynthesis
Sunlight energyfood energy
Plants and algae are autotrophs
They just need CO2 and light to make food
Key to the first steps in photosynthesis are
pigments
Light is part of the electromagnetic spectrum
Low energy/high wavelength/low frequency
High energy/ low wavelength/high frequency
InfraredROYGBIVUltraviolet
When pigments absorb light, they get charged up
(reduced)
6H20 + 6CO2  6O2 + C6H12O6
Low energy  high energy
Endergonic
1) Light dependent reactions (require light)
Sunlight energy  electron carriers (reduced
molecules) ATP and NADPH
2) Light independent reactions (require CO2)
Electron carriers  sugar molecules
Chloroplasts contain stacks of thylakoids; stacks
are called grana. More thylakoids=more
photosynthesis.
Photosystem II
Energy from sunlight is used to make P680 a very
powerful reducing agent, powerful enough to
reduce water
H2O  oxygen + hydrogen
Electrons are removed from water (low energy
state); raised to a high level of energy
Electrons flow down electron transport chain,
Energy is used to make ATP (high energy)
Photosystem I
Takes sunlight energy, raises electron energy
again, electrons flow down a second electron
transport chain, energy used to NADP+NADPH
NADPH (reduced, high energy)
Light independent reactions (Calvin Cycle)
ATP + NADPH + CO2  G3P (very small, 3
carbon sugar)
Sometimes the Calvin Cycle is delayed following
the Light Dependent Reactions.