PHOTOSYNTHESIS“The Process That Feeds the Biosphere”
Terminology
Heterotrophs Photoautotrophs
Important Structures
Chloroplast Chlorophyll
(pigment) Stomata Thylakoid Grana Stroma
Photosynthesis
CO2 + H2O + light C6H12O6 + O2
Photosynthesis
Organisms split water as a source of electrons, then release O2
Electrons reduce CO2 to sugars (increase in ΔG requires energy)
Two Stages
Light Reactions Light absorbed
creates NADPH Water split ATP produced Photophosphorylati
on Thylakoids
Calvin Cycle Carbon fixation Uses NADPH and
ATP Stroma
Light
Visible wavelengths drive photosynthesis
Chlorophyll a and chlorophyll b absorb different wavelengths
Carotenoids = photoprotection
Photosystems
Pigments and proteins
Absorbed energy funneled to reaction center
Photosystems II and I absorb different wavelengths of light
Non-cyclic Electron Flow
PS II electron excited to PEA
Water split to replace lost electrons (O2 formed)
Electron passed down ETC to PS I, providing energy for ATP
Repeat process in PS I NADP+ reduced by 2 e-
to NADPH
Non-cyclic Electron Flow
Cyclic Electron FLow
No use of PS II Rise in NADPH levels triggers cyclic flow
that creates only ATP
Electron Transport / ATP Synthesis
Similar proton-motive force in chloroplasts
DIFFERENCES:• Where electrons come
from• H+ reservoir area