1. Chapter 7 PHOTOSYNTHESIS

2. Life Depends on Photosynthesis ] What if there is a nuclear winter? F What is it F What would cause it? F What are the repercussions?

3. What is a photosynthate? ] Glucose and other carbohydrates F Runs photorespiration F Makes amino acids, starch, cellulose, rubber, quinine, spices, etc

4. Who came first: Autotrophs or Heterotrophs ? ] Heterotrophs CREATED a heavy CO 2 atmosphere. F Almost became extinct when resources disappeared. F Environmental pressure allowed heterotrophs to begin to photosynthesize F Autotrophes kick out TONS of O 2

5. Who came first: Autotrophs or Heterotrophs?, con’t ] How did the rise of autotrophes change the earth? F Decrease CO 2 in atmosphere so climate got cold F Created polar ice caps F Lowered ocean levels F O 2 levels increased to above today’s levels v Jurassic – much higher ARE LEVELS STABLE NOW?????

7. A. Light Visible light makes up only a small portion of the electromagnetic spectrum. Sunlight consists of: ] 4% Ultraviolet (UV) radiation ] 44% Visible light ] 52% Infrared (IR) radiation

8. Characteristics of Visible Light: is a spectrum of colors ranging from violet to red (ROY G BIV) is a spectrum of colors ranging from violet to red (ROY G BIV) consists of packets of energy called photons photons travel in waves, having a measurable wavelength ( λ ) λ = distance a photon travels during a complete vibration [measured in nanometers (nm)]

9. A photon’s energy is inversely related to its wavelength...photon’s energy...the shorter the λ, the greater the energy it possesses. Which of the following photons possess the greatest amount of energy? Green photons λ = 530nm Red photons λ = 660nm Blue photons λ = 450nm

10. What happens to light when it strikes an object? reflected (bounces off) Only absorbed wavelengths of light function in photosynthesis. Visible light provides just enough energy to “excite” or energize molecules transmitted (passes through) absorbed

11. B. Photosynthetic Pigments Molecules that capture photon energy by absorbing certain wavelengths of light. 1. Primary pigments Bacteriochlorophyll - green pigment found in certain bacteria. Chlorophylls a & b - bluish green pigments found in plants, green algae & cyanobacteria.

12. Chlorophyll a is the dominant pigment in plant cells. Central Mg atom with 4 N atoms –area where energy transfer occurs Tail anchors molecule to chloroplast

13. 2. Accessory Pigments Carotenoids - red, orange, yellow pigments found in plants, algae, bacteria & archaea. Xanthophylls – red and yellow pigments found in plants, algae & bacteria. Fucoxanthin – brown pigment found in brown algae, diatoms, & dinoflagellates Phycoerythrin - red pigment found in red algae. Phycocyanin - blue pigment found in red algae & cyanobacteria. Bacteriorhodopsin – purple pigment found in halophilic archaea Each pigment absorbs a particular range of wavelengths.

15. C. Chloroplasts (hyperlink chloroplasts)Chloroplasts Sites of photosynthesis in plants & algae. Concentrated in mesophyll cells of most plants.

16. Chloroplast structure: Stroma - gelatinous matrix; contains ribosomes, DNA & various enzymes. Thylakoid - flattened membranous sac; embedded with photosynthetic pigments.

17. D. Photosynthesis Occurs in two stages: Light reactions (pink hyperlink)- harvest photon energy to synthesize ATP & NADPH. Light reactions Carbon reactions (Calvin cycle) - use energy from light reactions to reduce CO 2 to carbohydrate. 6CO 2 + 12H 2 O  C 6 H 12 O 6 + 6O 2 + 6H 2 O

18. Overview of Photosynthesis

19. 1. Light ReactionsLight Reactions require light occur in thylakoids of chloroplasts involve photosystems I & II (light harvesting systems). Photosystems contain antenna complex that captures photon energy & passes it to a reaction center.

20. Light Reactions of Photosynthesis

21. LIGHT REACTION Uses light and water Synthesizes ATP and NADPH O2 released here (comes from water) Begins in thylakoid membrane 4 clusters of proteins involved 2 clusters make 2 photosystems other 2 clusters form electron transport chain (ETC) notice different light lengths

22. Light Reaction, con’t Photosystem II happens first SUN Antenna Complex Chlorophyll a in reaction center P680 e-e- 1 st carrier molecule in ETC Energy (electron) goes to Photosystem I ATP, produced from ADP, comes out of thylakoid and into stroma for Calvin cycle Powers Calvin Collects photons sends electrons Receives electrons sends electrons Redox reactions Oxygen is released here when H 2 O is split

23. Light reaction, con’t Photosystem I is next Sun 1 st carrier molecule in new ETC Antenna complex Electrons change (reduce) NaDP + to NaDPH Chlorophyll a in reaction center P700 e-e- Powers Calvin

24. ATP Production ATP Production by Chemiosmotic Phosphorylation

25. 2. Carbon Reactions (Calvin cycle; C 3 cycle) do NOT require light (occur in both darkness & light as long as ATP & NADPH are available) occur in stroma of chloroplasts require ATP & NADPH (from light reactions), and CO 2

26. Calvin Cycle

27. CALVIN CYCLE (aka carbon cycle, aka C 3 cycle) Found in plants that only use calvin: cereals, peanuts, tobacco, spinach, most trees and lawn grasses C3 named for 3 carbon compound: phosphoglyceric acid (PGA)- 1st stable compound in pathway Calvin – discovered this system Goal of calvin cycle: Fix C from CO2 into organic compounds (glucose) Occurs in both light and dark (as long as ATP and NADPH is available CO2 enters through stoma (plural: stomata) Powered by ATP/NADPH from light reaction Diagram on pg 117 is good Rubisco – most abundant and important protein in the world 85% of plants use this system

28. Calvin cycle, con’t RuBp (ribulose Biphosphate CO 2 from the atmosphere Unstable 6 Carbon molecule PGA 3-C PGA 3-C Combines with (assisted by rubisco- an enzyme) (uses ATP and NADPH as energy from LR) Becomes More ATP & NADPH used here PGAL C 3 H 6 O 3 Converts to glucose then to other carbohydrate Can be rearranged to form RuBP (starts cycle over) (Phosphoglyceraldehyde: 1 st carbohydrate product of Calvin) (C 3 H 6 O 3)

29. Plants that use only the Calvin cycle to fix carbon are called C 3 plants. Ex. cereals, peanuts, tobacco, spinach, sugar beets, soybeans, most trees & lawn grasses.

30. Photosynthetic Efficiency ] Only.037% of atmosphere is CO 2 ] Yet 200 billion tons of carbon (from CO 2 used to make glucose ] If each photosystem gets all the CO 2 possible, efficency is only 30%- reality is much lower! ] Cloudy days are only.1% efficient ] Cultivated plants only 3% efficient ] Greatest natural efficiency – evening primrose – 8% ] Sugarcane – 7%

31. E. Photorespiration Process that counters photosynthesis. Occurs when stomata close under hot, dry conditions: O 2 levels in plant increase CO 2 levels in plant decrease Under these conditions, rubisco fixes O 2 (rather than CO 2 ). Thus, PGAL is NOT produced.

32. Photorespiration ] Occurs when conditions are low CO2 or high O2 ] Rubisco uses O2 instead of CO2 as substrate ] Results in loss of Carbon for calvin (carbon) reaction ] High temperatures complicate things: fixing and releasing CO2 occurs at the same rate. No net C gain, no glucose produced ] Stomata too open (trying to get more CO2) means dehydration

33. C 4 Photosynthesis Adaptations that allow certain plants to conserve water and reduce photorespiration at higher temperatures. ] Found in sugarcane, corn, millet, sorghum, all flowering plants in hot, open environments (about.4% of all plants) ] Use 4-carbon compound to concentrate carbon within special cells ] CO2 is fixed in mesophyll cells first ] This keeps CO2 concentration 20-120 times greater than in C3 cycle ] Not efficient in normal climates: used 2 ATP for every carbon that is moved from the mesophyll cells ] Then it is fixed as normal via Calvin cycle ] These plants require about half as much water due to recycling of compounds during the pathway

34. C 4 Respiration C 4 plants reduce photorespiration by physically separating the light reactions and Calvin cycle. C4 plants even fix CO2 when stomata begin to close – preserves water – plants require ½ the water of C3 CO 2  malic acid  migrates to bundle sheath cells and enters C 3  glucose (instead of PGA)

35. Leaf anatomy of a C 4 plant C 4 Photosynthesis: Light reactions occur in chloroplasts of mesophyll cells. Calvin cycle occurs in chloroplasts of bundle sheath cells.

36. 2. CAM Photosynthesis CAM plants reduce photorespiration by acquiring CO 2 at night. Night: mesophyll cells fix CO 2 as malic acid malic acid is stored in vacuoles. Day: malic acid releases CO 2 which enters Calvin cycle. Malic acid

37. CAM (crassulcean acid metabolism)Respiration ] Includes cacti, pineapple, Spanish moss, orchids, some firns and wax plants (10% of all plant species) ] Take in CO2 at night ] Fix it in calvin cycle the next day ] Stomata stay closed during the day to preserve water ] Plants acidic at night – more alkaline in day ] Malic acid formed in large vacuoles in same cells that contain chloroplasts ] Malic acid enters chloroplast during the day where C3 begins