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Chapter 8 Photosynthesis. Trophic Roles Autotrophs produce organic molecules from CO 2 & inorganic raw materials producers plants Heterotrophs consumers.

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Presentation on theme: "Chapter 8 Photosynthesis. Trophic Roles Autotrophs produce organic molecules from CO 2 & inorganic raw materials producers plants Heterotrophs consumers."— Presentation transcript:

1 Chapter 8 Photosynthesis

2 Trophic Roles Autotrophs produce organic molecules from CO 2 & inorganic raw materials producers plants Heterotrophs consumers

3 Chloroplast Structure Found in mesophyll 1 mesophyll cell may have 30 chloroplasts Stomata regulate passage of CO 2, O 2 and H 2 O

4 Chloroplast Structure

5 Chloroplast Structure (cont.) Pigments light receptors Absorb light energy Boost e - Chlorophyll Chlorophyll a main pigment blue-green Chlorophyll b accessory pigment yellow-green Accessory pigments absorb different wavelengths of light Carotenoids yellow- orange

6 Photosystems Pigment molecules absorb energy boost electrons unstable Passes energy to reaction center of antenna complex (chlorophyll a molecule) transfers energy to primary electron acceptor

7 Photosynthesis Light reactions Cyclic photophosphorylation Non-cyclic photophosphorylation Photolysis (breaking water up with light) Dark reactions Calvin Cycle

8 Photosystems (cont.) Located in thylakoid membrane Photosystem I P700 absorbs light of 700 nm Photosystem II P680 absorbs light of 680 nm Both are primarily chlorophyll a Electron acceptor NADP + NADPH

9 Non-cyclic photophosphorylation

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15 LIGHT REACTOR NADP + ADP ATP NADPH CALVIN CYCLE [CH 2 O] (sugar) STROMA (Low H + concentration) Photosystem II LIGHT H2OH2O CO 2 Cytochrome complex O2O2 H2OH2O O2O2 1 1 2 2 Photosystem I Light THYLAKOID SPACE (High H + concentration) STROMA (Low H + concentration) Thylakoid membrane ATP synthase Pq Pc Fd NADP + reductase NADPH + H + NADP + + 2H + To Calvin cycle ADP P ATP 3 H+H+ 2 H + +2 H + 2 H +

16 Cyclic Photophosphorylation Primitive used by bacteria only generates energy-- no glucose Electron boosted out of PI ETC returned to PI Electron drives proton pump chemiosmosis ATP

17 Calvin Cycle aka Dark Reactions Occur in the dark or the light Light independent reactions 3 steps Carbon fixation Reduction Regeneration of RuBP

18 Step 1: Carbon Fixation RuBP (ribulose bisphosphate) 5 C sugar catalyzed by RuBP carboxylase (Rubisco) unstable compound (splits) PGA

19 Step 2: Reduction Phosphorylated by ATP Reduced by NADPH Produces pyruvate some pyruvate glucose most pyruvate regenerate RuBP

20 Step 3: Regeneration of RuBP Pyruvate rearranged into RuBP Requires input of 3 ATP Takes 12 turns of cycle 1 glucose

21 http://www.science.smith.edu/departments/Biology/Bio231/calvin.html

22 Alternative mechanisms: Photorespiration Competitive reaction between RuBP, CO 2 and O 2 Rubisco substitutes O 2 for CO 2 2 C compound (phosphoglycerate) Eventually broken down releases CO 2 Non-productive C 3 plants rice, wheat, soybeans (hot, bright days) Photo (light) respiration( releases CO 2 /consumes O 2 )

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24 Alternative mechanisms: C 4 Plants Sunny ecosystems Carbon fixed outside cells (in bundle sheath cells very efficient requires extra ATP Balances out photorespiration Corn is a C 4 plant

25 Alternative mechanisms: CAM Plants Crassulacean acid metabolism Hot/dry climates Orchids, cacti, etc. Stomates open at night to reduce water loss evaporation CO 2 is fixed, used later

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