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Photosynthesis: Nature’s Greatest Gift to Life. I. A Historical Perspective: CO 2 + H 2 O C 6 H 12 O 6 + O 2 A. Old View: CO 2 is Split, H 2 O stays intact.

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Presentation on theme: "Photosynthesis: Nature’s Greatest Gift to Life. I. A Historical Perspective: CO 2 + H 2 O C 6 H 12 O 6 + O 2 A. Old View: CO 2 is Split, H 2 O stays intact."— Presentation transcript:

1 Photosynthesis: Nature’s Greatest Gift to Life

2 I. A Historical Perspective: CO 2 + H 2 O C 6 H 12 O 6 + O 2 A. Old View: CO 2 is Split, H 2 O stays intact CO2O2 +H2OH2OC 6 H 12 O 6 +O2O2 Why this Explanation Made Sense 1.Oxygen stays as a gas in the same ratio 2.Water has a 2:1 ratio as the carbohydrate B. New View: Water is Split, CO 2 stays intact CO 2 +H2H2 O+C 6 H 12 O 6 O2O2 Why the change in views? 1.When water was tagged with an O 2 isotope, the tag was on the released O2, not the glucose CO 2 + H 2 O C 6 H 12 O 6 + O 2 2.When CO 2 was tagged with the O 2 isotope, the tag was found in the glucose, not the released O 2 CO 2 + H 2 O C 6 H 12 O 6 + O 2

3 Organ Tissue Cell Organelle SO.. … What’s The Point? 1.The structures of a leaf must provide for the function of photosynthesis 2. The chloroplast is the func- tional unit of photosynthesis The Structure Leaf and Photosynthesis light chlorophyll enzymes CO 2 + H 2 O C 6 H 12 O 6 + O 2

4 II. The 2 Stage Process of Building Glucose Light Dependent reactions Light H2OH2O Light Independent Reactions Calvin Cycle CO 2 O2O2 ADP NADP ATP NADPH C 6 H 12 O 6 Light reactions provide Raw Materials for the “Dark” reaction 1. ATP 2. H+ (NADP) The “Dark” Reactions are building Glucose from CO2 Stage #1 Stage #2

5 III. Energy from Light (I hope you remember your physics) SO.. … What’s The Point? 1. Visible light comes in different wave lengths and energy levels 2. The pigments seen are due to different wavelengths and energy levels “Not all wavelengths are created equal”

6 SO.. … What’s The Point? 1.The color observed is the color reflected (transmitted) 2.All other colors are absorbed 3.Reflected light cannot be used for photo- synthesis because it does not absorb any light energy Why does a dark car heat up faster in the sun than a light? What would be the worst color light to use as a plant growth light? Related Questions

7 SO.. … What’s The Point? 1. ________ color is the best light for photosynthesis. The runner-up is ________ 2. The advantage to having yellow and red pigments in leaves and not just green is________

8 Go to Socrative on your cell phone. My room # is BRADYAPBIO 1.What leaf structure allows for gas exchange? a.chloroplastc. inner membrane b.stomatad. chlorophyll 2. What is the source of oxygen that is released from plant cells as a result of photosynthesis? a.carbon dioxidec. glucose b.ATPd. water

9 3. Based on the absorption spectrum in your notes, what wavelength of light is absorbed the most during photosynthesis? a.700 nmc. 450 nm b.600 nmd. 550 nm 4. Carbon dioxide becomes ______ in photosynthesis, forming glucose. a.reducedc. charged b.oxidizedd. broken down 5. Photosynthesis converts _______ energy into chemical energy in the form of glucose. a.lightc. electrical b.chemicald. thermal

10 Light Pigment E- Green Light Reflected Heat Fluorescence E- IV. How pigments react to light energyHow pigments react to light energy 1. Photosynthesis captures the energy from the excited electron to make ATP SO.. … What’s The Point? 2.The ATP is then used to build Glucose ATP

11 V. The Light Dependent Reactions Light Stroma Thylakoid space Thylakoid Chloroplast Grana Thylakoid Stroma PS II (P680) PS I (P700) H2OH2O O2O2 H+ ATP NADPH Calvin Cycle H+ E- Pq H+ Pump PC E- Fd E- H+ NADP Reductase H+ ADP Proton Motive Force ATP Synthase Chemiosomosis ADP Photophosphorylation 1. Cyclic 2. Non-Cyclic Stroma

12 Cyclic verses Non-Cyclic Photophosphorylation Non-Cyclic 1. Electron from water never “recycles” 2. Electron used to make NADPH 3.Requires Photosystem I and II 4.Takes place when plenty of H+ and ATP available (H 2 0 is plentiful) Cyclic 1.Electron recycles 2.Electron used to fill the empty electron hole 3.Only uses Photosystem I 4.Makes ATP even though H2O is unavailable

13 VI. The Calvin Cycle- Building Compounds 1 Carbon at a Time CO 2 Rubisco Phase 1 Carbon Fixation RuBP Unstable 6 Carbon compound (2) PGA (2) Bucket O’ PGAL Krebs Cycle 1. Amino Acids - Proteins 2PGAL = C 6 H 12 O 6 PhotosynthesisPhotosynthesis fills the PGAL Bucket for many metabolic products (2) PGAL(2) PGAL/G3P ATP NADPH NADP ADP Phase 2 Reduction (Ribulose BiPhosphate Carboxylase ) Ribulose BiPhosphate PGAL ATP ADP Pi 3c 5c Phase 3 Regeneration of CO2 Acceptor Making the numbers balance 2. Glycerol & Fatty Acids- Lipids Carbon dioxide acceptor (3 - 5C RubBP) (3 - 6C Unstable compounds ) (6 - 3C Stable compounds) (5 - 3C Stable compounds) Rearrangement of carbons (3 CO 2 molecules enter)

14 How Photosystems Harvest Light Slide 11

15 Photorespiration: The Dark Side of Photosynthesis The Problem: Rubisco CO 2 Calvin Cycle 2 PGAL (3C) O2O2 PGAL (3C) (2)CO 2 6 Carbon Results 1.1 Carbon gained (per turn) 1. Two carbons lost (per turn) Rubisco has an affinity to CO2 and O2. Conditions that Magnify the Problem: 1. Bright Days (High Photosynthesis) O2O2 O2O2 O2O2 O2O2 2. Dry Days (Stomata close due to water loss) Evolutionary Origins: Rubisco is an “Evolutionary Relic” that evolved in a low O 2 environment (What’s the worse case scenario?) H2OH2O H2OH2O H2OH2O H2OH2O 2.RuBP bucket refilled ( What biomes would be most affected by photorespiration?) RuBP 5 Carbon Bucket O’RuBP NormalPhotorespiration Glucose 2. RuBP bucket only emptied C3 Plants

16 Solution To the Problem: Keep Rubisco Away from High Oxygen Concentrations!!!! Strategy #1 Name: C4 Metabolism Plant Type:Grasses, Grains Description: 2. The 4 Carbon compound (C4) is transported to Bundle Sheath cells where an enzyme breaks it down to release CO 2Bundle Sheath Strategy #2 CAM (Crassulacean Acid Metabolism) Succulents (cactus) 1. Stomata only open at night (saves water) and store CO 2 as crassulacean acid 2. Stored CO 2 is released during the day as needed in the Calvin cycle 1. CO 2 bonds to a 3 Carbon Compound in Mesophyll cells Differences:Differences Alike CO 2 Organic Acid Rubisco Calvin Cycle PGAL Structure Mesophyll Bundle Sheath Time DAY Night 1. CO 2 incorporated into a 4 carbon organic acid 2. Organic acid releases CO 2 into Calvin Cycle


18 Note: All C4 plants are easy to identify by the presence of the unique Bundle Sheaths and Mesophyll cells Plasmodesmata Slide 13

19 Photosystem II sends electrons to a higher energy level Slide 9

20 E- Electron Acceptor 1. Pq (Plastiquione) 2. FD (Ferredoxin) Light Antenna Pigments Chlorophyll a Donates the electron Photosystem E- How does chlorophyll “a” refill its electrons? 1. Chlorophyll “b” 2. Carotene 3. Xanthophyll Reaction Center

21 The Structure of Chlorophyll Embedded in the membrane On membrane surface Metal that allows transfer of electrons Slide 11

22 Slide 8


24 Slide 7

25 SLIDE 11

26 The Metabolic Possibilities of PGAL Slide 11

27 PGAL H PGA Cell Respiration (Glycolysis) PGAL H 2PGA 1,3-Biphosphoglycerate Pyruvic Acid CO 2 + Ribulose Bi Phosphate Unstable 6 Carbon ATP Slide 11 Photosynthesis (Calvin Cycle) Vs.

28 Slide 9

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