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