Photosynthesis. I. Photosynthesis overview A. Purpose B. Location. The light vs. the dark reaction Chloroplasts pigments A. Light absorption B.

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2 Photosynthesis I. Photosynthesis overview A. Purpose B. Location II. III. The light vs. the dark reaction Chloroplasts pigments A. Light absorption B. Types IV. Light reactions A. Photosystems B. Photophosphorylation V. The light independent reaction ( dark reaction) A. Carbon fixation B. Reduction C. Regeneration VI. Alternative plants

3 Photosynthesis - overview

4 Photosynthesis - overview Overall purpose: photosynthesis light chemical energy complements respiration Energy for all life on earth ultimately comes from photosynthesis

5 Cellular Respiration vs. Photosynthesis Cellular Respiration: (Exergonic) Photosynthesis: (Endergonic)

6 Photosynthesis chloroplast recap Outer membrane Inner membrane Thylakoid membrane Stroma Thylakoid space Intermembrane space

7 Photosynthesis - overview Photosynthesis - 1. light rxn: store energy & split water photo NADPH & ATP 2. dark rxn: fix CO 2 & make sugars synthesis Calvin cycle

8 Redox Reactions 6CO H 2 O + light energy Equation for photosynthesis C 6 H 12 O 6 + 6O 2 + 6H 2 O

9 light reactions: thylakoid membrane thylakoid space Photosynthesis - overview H 2 O CO 2 dark reactions: stroma Light Light Reactions NADP + ADP + P ATP NADPH Calvin Cycle Chloroplast O 2 [CH 2 O] (sugar)

10 Photosynthesis light absorption visible light ~380 to 750 nm chloroplast pigments abs blue-violet & red - transmit and reflect green

11 Photosynthesis light absorption pigments: chlorophyll a -energy-absorbing ring -hydrocarbon tail accessory pigments - chlorophyll b - carotenoids - photoprotective

12 Photosynthesis light absorption chlorophyll a abs blue-violet, red , nm chlorophyll b & carotenoids abs broadly blue-violet mid-400s more wavelengths used for photosynthesis = more light energy absorbed

13 Photosynthesis light absorption Pigments have two states: ground & excited chlorophyll abs light e- excited more energy energy transferred

14 Photosynthesis light absorption Pigments are held by proteins in the thylakoid membranes light harvesting complex energy absorbed from light - to pigments to reaction center - two special chlorophyll a - proteins - 1 electron acceptor light harvesting complex & reaction center = photosystem (PS)

15 Photosynthesis energy transfer STROMA Light Photosystem II Light Photosystem I THYLAKOID SPACE Thylakoid membrane Photosystem I (PS I) & PS II Difference light wavelength, proteins, where e- from

16 Photosynthesis energy transfer PSII: absorbs 680 nm, splits water, powerful ETC, ATP made PS I: absorbs 700 nm, e- from PSII, short ETC, NADPH made (less energy)

17 Photosynthesis energy transfer e- in PS II, from split H 2 0 e- from PS II electron transport chain (ETC) PS I e- from PS I 2 nd ETC e- carrier: NADP+ NADPH

18 Photosynthesis chemiosmosis How is ATP produced? Chemiosmosis e- down ETC, H+ to thylakoid space H+ conc. gradient H+ down gradient, ATP synthase photophosphorylation

19 Light reaction - summary inputs: light energy, H 2 O PS II, ETC, PS I, ETC outputs: ATP NADPH O 2 (waste)

20 Self-Check Step of Photosynthesis Location IN chloroplast Inputs Outputs ATP produced? e- carriers loaded? (don t need #) Light reaction overall PSII PSI Dark reaction overall Know figures of chloroplast reactions/locations!

21 Photosynthesis energy transfer

22 Dark reaction (Light-independent Reaction) 6CO H 2 O + light energy C 6 H 12 O 6 + 6O 2 + 6H 2 O Dark reaction: Calvin cycle H 2 O CO 2 regenerative anabolic Light NADP + ADP + P i RuBP 3-Phosphoglycerate Calvin Cycle CO 2 in, sugar out ATP NADPH G3P Starch (storage) during daylight Chloroplast O 2 Sucrose (export)

23 3 stages of Calvin-cycle: Carbon fixation #1 carbon fixation CO 2 link to 5-C 5-C: ribulose bisphosphate (RuBP) - enzyme: Rubisco 6-C unstable split 2(3-C) abundant

24 3 stages of Calvin-cycle: Reduction #2 reduction 3-C reduced e- from NADPH reduced 3-C: G3P

25 3 stages of Calvin-cycle: #3 regenerate C-acceptor Regeneration of C-acceptor still 5 G3P 3 RuBP multiple steps uses ATP every 3 cycles: 1 G3P made 3 RuBP regenerated C 3 plants CO 2 fixed into 3-C

26 Self-Check Step of Photosynthesis Location IN chloroplast Inputs Outputs ATP produced e- carriers loaded (don t need #) Light reaction overall PSII PSI Dark reaction overall

27 Alternate methods of C fixation

28 Alternate methods of C fixation CO 2 in stomata H 2 O CO 2 Light open, lose water NADP + ADP + P i hot, dry open stomata less; lowers water loss, lowers CO 2 Chloroplast ATP NADPH O 2 fixed photorespiration inefficient RuBP 3-Phosphoglycerate Calvin Cycle G3P Starch (storage) O 2 fix CO 2 into 4-C molecules Sucrose (export)

29 Photosynthesis summary light reaction: Light energy + H 2 O O 2, NADPH, ATP Thylakoids light-independent: CO 2, NADPH, ATP G3P (sugar), RuBP Stroma

30 Photosynthesis summary Where do photosynthetic products go?

31 Photosynthesis in context of big picture