1. Photosynthesis
Ch.6

3. (6-1) Photosynthesis
Biochemical pathway that converts light E into chemical E (organic cmpds/ carbs)

4. Obtaining E Autotrophs: use E from sun to make food
Plants, algae, some bacteria
Heterotrophs: get E from food they consume
Humans, birds

5. Overview 2 step process:
Light Rxn: light E is converted to chemical E & temporarily stored in ATP & carrier molecule NADPH
Calvin Cycle (Dark Rxn): organic cmpds formed using CO2 & stored chemical E

6. Capturing Light E
Light rxns begin w/ absorption of light in chloroplasts
Inside a chloroplast are thylakoids stacked to form grana surrounded by stroma

8. Light & Pigments
White light strikes an object & it’s colors are reflected or absorbed
Pigments: cmpds that absorb light
Colors not absorbed will be reflected back & seen

9. Light E from the Sun

10. Chloroplast Pigments
Thlyakoid membranes have pigments that absorb light E
Chlorophyll a: impt. in light rxns
Accessory pigments: assist in capturing light E
Chlorophyll b
Carotenoids

11. Why so many pigments?

12. Light Rxns Light E excites pigment e-
Photosystem 1 & 2
e- donated to e- transport chain (ETC)
Moves protons (H+) into thylakoid
Makes NADPH

13. Importance of H2O
e- replacement in PS2 needs to occur or photosynthesis stops
e- provided by H2O

14. Chemiosmosis
Making ATP using a chemical conc. gradient of H+ ions (from H2O) across the thylakoid membrane via the protein ATP synthase

18. (6-2) Calvin Cycle
Plants use E stored in ATP & NADPH during light rxns to produce organic cmpds (sugars)
Not dependent on light!
Carbon fixation: C-atoms from CO2 bonded into sugars

19. Carbon Fixation CO2 diffuses into stroma, combines with RuBP, & splits
                       
CO2 diffuses into stroma, combines with RuBP, & splits
1 new molecule uses E (ATP & NADPH) to leave the cycle to make carbs
1 new molecule gets converted back to RuBP & restarts cycle

21. Stomata
Small pores on the undersides of leaves that allow gas exchange
When stomata are partially closed H2O loss can be dec., but CO2 levels also dec., which inhibits C-fixation

22. CO2 in; H2O & O2 out

23. Alternative Pathways C4: fix carbon into a 4-C cmpd
Partially close stomata during hottest part of day
Ex: corn, sugar cane, crab grass
CAM: operates at night
Close stomata during the day
Ex: cacti, pineapples

25. Rate of Photosynthesis
Affected by:
Light intensity
CO2 level
Temp.