1. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Photosynthesis Copyright © McGraw-Hill Companies Permission required for reproduction or display

2. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Chloroplast Organelle found in plants and photosynthetic organisms Major site of photosynthesis Located in the cells of mesophyll Contains the pigment chlorophyll

3. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Structure of Chloroplast: Internal membranes organized into sacs of thylakoids (coins) and stacked to form granum or grana (stack of coins). Semiliquid fluid (stroma) surrounds thylakoid membrane.

4. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Functional Unit of a Chloroplast * photosystems - photosynthetic pigments clustered in membranes of thylakoids. - when light of proper wavelength strikes a pigment molecule, excitation of electrons pass from one molecule to another.

5. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Biophysics of Light Light moves through the air as oscillating electric and magnetic fields.  Energy content of a photon is inversely proportional to the wavelength of light. - Short wavelengths contain photons of higher energy than long wavelengths.

6. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies (Biophysics of Light) Ultraviolet Light  Shorter wavelength and more energy than visible light. Absorption Spectrum - the range and efficiency of photons a molecule is capable of absorbing.  When a photon strikes a molecule, its energy is either lost as heat or absorbed by the electrons boosting them into higher energy levels.

7. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies (Biophysics of Light) Pigments – molecules that absorb light  Photosynthesis uses two pigments: - Chlorophyll and Carotenoids

8. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Two types of Chlorophyll in green plants: 1. Chlorophyll a (main pigment) 1. Acts directly to convert sunlight to chemical energy 2. Chlorophyll b (accessory pigment) 1. Increases the proportion of the photons in sunlight that plants can harvest 2. has an absorption shifted toward green wavelengths. 3. Absorbs yellow and green light

9. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

10. Chlorophylls and Carotenoids All plants, algae, and cyanobacteria use chlorophyll a as their primary pigment.  Achieve higher overall photon capture rates with chlorophyll than with other pigments. Carotenoids absorb photons with a wide array of energies, but are not as efficient in transferring energy as chlorophyll.

11. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Three Stages of Photosynthesis:  Capture energy from sunlight.  Use energy to make ATP and NADPH.  Use ATP and NADPH to fix carbon. ATP (adenosine triphosphate) – energy is stored in bonds between phosphate groups. NADP + (nicotineamide adenine dinucleotide phosphate) – temporarily stores energized electrons; proton carrier NADP + → NADPH (oxidized)(reduced)

12. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Organizing Pigments Into Photosystems Light reactions take place in four stages:  Primary Photoevent (electron acceptor)  Charge Separation  Electron Transport  Chemiosmosis Light is absorbed by clusters of chlorophyll and accessory pigments collectively called a photosystem.

13. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Organizing Pigments Into Photosystems Photosystem consists of two components:  Antenna Complex - Captures photons from sunlight.  Reaction Center - Pair of chlorophyll a molecules act as trap for photon energy, passing an excited electron to an acceptor.

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15. Photosystem Function Bacteria Use a Single Photosystem  Electron joined with a proton to make hydrogen.  Electron is recycled to chlorophyll. - Electron transfer process leading to ATP formation is termed cyclic phosphorylation.  Major limitation is that it is only geared towards energy production, not biosynthesis.

16. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Photosystem Function Plants Use Two Photosystems  Photosystem I – reaction center chlorophyll is known as P700; absorbs light having  ג= 700nm  Photosystem II (P680)uses another arrangement of chlorophyll a to absorb more shorter wavelength, high energy photons. - Enhancement Effect

17. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Photosystems I and II Copyright © McGraw-Hill Companies Permission required for reproduction or display

18. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Two Photosystems Work Together Two-stage photosystem referred to as non- cyclic phosphorylation.  Photosystem II acts first. - High energy electrons generated by photosystem II used to synthesize ATP, and then passed to photosystem I to drive NADPH production.

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20. Calvin Cycle Phase I – Carbon Fixation Calvin Cycle begins when CO 2 binds RuBP to form PGA. Also called C 3 photosynthesis. Carbon fixation is made possible due to the attachment of CO 2 to ribulose 1, 5- bisphosphate (RuBP); rubisco.  6C molecule is unstable and forms two three-carbon molecules of phosphoglycerate (PGA or 3PGA).

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22. Summary of Calvin Cycle Phase II- CO 2 reduction (1) PGA forms (2) G3P’s We need to go through 3 cycles to continue the production of carbohydrates, as a result we need 3 CO 2 to form (6) G3P’s of these:  (1 C) of the G3P’s (precursor of a sugar molecule) goes to form Carbohydrates  (5 C) of the G3P’s goes to reforming rubisco  Cycle uses (6) ATP and (6) NADPH to generate (6) G3P and the cycle uses (3) ATP to regenerate rubisco.

23. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Photorespiration Photorespiration incorporates O 2 into ribulose1,5-bisphosphate and releases CO 2.  Under normal conditions, 20% of photosynthetically-fixed carbon is lost to photorespiration. - Loss rises as temperature increases. C 4 photosynthesis produces a four carbon compound which does not go through photorespiration.

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25. Decreasing Photorespiration C 4 plants conduct photosynthesis in mesophyll cells and the Calvin Cycle in bundle sheath cells.  Creates high local levels of CO 2.  Examples: corn, sugarcane, grasses Crassulacean Acid Metabolism (CAM) plants open stomata during the night and close them during the day to minimize water loss.  Use C 4 during the night and C3 during the day.  Examples: Pineapples, cacti, succulent plants  Used to reduce photorespiration

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27. Review Chloroplasts Biophysics of Light Chlorophylls and Carotenoids Photosystems Calvin Cycle Photorespiration

28. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Copyright © McGraw-Hill Companies Permission required for reproduction or display