Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water, and carbon dioxide to produce oxygen and energy in the form of sugars. It occurs in two stages - the light reactions where light is absorbed to produce ATP and NADPH using chlorophyll, and the Calvin cycle where ATP and NADPH are used to fix carbon and produce sugars. The light reactions take place in the thylakoid membranes of chloroplasts and involve two photosystems that absorb different wavelengths of light and an electron transport chain that creates a proton gradient to produce ATP.

1. Photosynthesis “The Process That Feeds the Biosphere”

2. Terminology Heterotrophs Photoautotrophs

3. Important Structures Chloroplast Chlorophyll (pigment) Stomata Thylakoid Grana Stroma

4. Photosynthesis CO2 + H2O + light  C6H12O6 + O2

5. Photosynthesis Organisms split water as a source of electrons, then release O2 Electrons reduce CO2 to sugars (increase in ΔG requires energy)

6. Two Stages Light Reactions Light absorbed creates NADPH Water split ATP produced Photophosphorylation Thylakoids Calvin Cycle Carbon fixation Uses NADPH and ATP Stroma

7. Light Visible wavelengths drive photosynthesis Chlorophyll a and chlorophyll b absorb different wavelengths Carotenoids= photoprotection

8. Photosystems Pigments and proteins Absorbed energy funneled to reaction center Photosystems II and I absorb different wavelengths of light

9. 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

10. Non-cyclic Electron Flow

11. Cyclic Electron FLow No use of PS II Rise in NADPH levels triggers cyclic flow that creates only ATP

13. H+ reservoir areaSimilar proton-motive force in chloroplasts