Ap Bio Ch7 Power Point

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Capturing Solar Energy: Photosynthesis

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  • Ap Bio Ch7 Power Point

    1. 1. Photosynthesis
    2. 2. What Is Photosynthesis? <ul><li>Early cells evolved the ability to perform photosynthesis about 2 billion years ago </li></ul><ul><li>Photosynthesis is the ability to capture sunlight energy and convert it to chemical energy </li></ul><ul><li>Most forms of life on Earth depend on the chemical energy produced by photosynthetic organisms </li></ul>
    3. 3. The Photosynthetic Equation 6CO 2 carbon dioxide + 6H 2 O water + light energy  sunlight C 6 H 12 O 6 glucose (sugar) + 6O 2 oxygen Photosynthesis occurs in plants, algae, and some prokaryotes Photosynthetic organisms are autotrophs (“self- feeders”) Photosynthesis in plants occurs within chloroplasts
    4. 4. Gases, Sugar, and Water Cycle <ul><li>Production of carbon compounds like glucose (photosynthesis) is linked with energy extraction (in cellular respiration) </li></ul><ul><li>Water, CO 2 , sugar, and O 2 cycle between the two processes </li></ul><ul><li>Photosynthesis and cellular respiration are interconnected </li></ul>
    5. 5. Interconnections: Photosynthesis & Respiration
    6. 6. Adaptations for Photosynthesis <ul><li>Leaves </li></ul><ul><li>Chloroplasts </li></ul>
    7. 7. Structures of Photosynthesis
    8. 8. Leaves <ul><li>Flattened leaf shape exposes large surface area to catch sunlight </li></ul><ul><li>Upper and lower leaf surfaces of a leaf comprise the epidermis </li></ul><ul><li>Waxy, waterproof cuticle on outer surfaces reduces water evaporation </li></ul>
    9. 9. Leaf Anatomy <ul><li>Adjustable pores called stomata allow for entry of air with CO 2 </li></ul><ul><li>Inner mesophyll cell layers contain majority of chloroplasts </li></ul><ul><li>Vascular bundles (veins) supply water and minerals to the leaf while carrying sugars away from the leaf </li></ul>
    10. 10. Internal Leaf Structure <ul><li>Internal leaf structure is crucial to photosynthesis since photosynthesis occurs primarily in the leaves of land plans </li></ul>
    11. 11. Leaf Structure Mesophyll Cells Upper Epidermis Lower Epidermis Vein Stoma
    12. 12. Anatomy of a Chloroplast <ul><li>Mesophyll cells have 40-200 chloroplasts each </li></ul><ul><li>Chloroplasts are bounded by a double membrane composed of the inner and outer membranes </li></ul>
    13. 13. Anatomy of a Chloroplast <ul><li>The stroma is the semi-fluid medium within the inner membrane </li></ul><ul><li>Disk-shaped sacs called thylakoids found within the stroma in stacks called grana </li></ul>
    14. 14. Chloroplast Structure Inner & Outer Membranes Thylakoids Granum Stroma (space)
    15. 15. The Energy in Visible Light <ul><li>The sun radiates electromagnetic energy </li></ul><ul><li>Visible light is radiation falling between 400-750 nanometers of wavelength </li></ul><ul><li>Packets of energy called photons with different energy levels </li></ul><ul><ul><li>Short-wavelength photons are very energetic </li></ul></ul><ul><ul><li>Longer-wavelength photons have lower energies </li></ul></ul>
    16. 16. Light, Chloroplast Pigments, & Photosynthesis Wavelength (nanometers, nm) Gamma Rays X-Rays UV Infrared Micro- waves Radio Waves Visible Light 400 450 500 550 600 650 700 750
    17. 17. Light Captured by Pigments <ul><li>Action of light-capturing pigments </li></ul><ul><ul><li>Absorption of certain wavelengths (light is “trapped”) </li></ul></ul><ul><ul><li>Reflection of certain wavelengths (light bounces back) </li></ul></ul><ul><ul><li>Transmission of certain wavelengths (light passes through) </li></ul></ul>
    18. 18. Light Captured by Pigments <ul><li>Absorbed light drives biological processes when it is converted to chemical energy </li></ul><ul><li>Common pigments found in chloroplasts include: </li></ul><ul><ul><li>Chlorophyll a and b </li></ul></ul><ul><ul><li>Accessory pigments such as carotenoids </li></ul></ul>
    19. 19. Light Captured by Pigments <ul><li>Chlorophyll a and b absorb violet, blue, and red light but reflect green light (hence they appear green) </li></ul><ul><li>Carotenoids absorb blue and green light but reflect yellow, orange, or red (hence they appear yellow-orange) </li></ul><ul><li>Pigment absorbs visible light </li></ul>
    20. 20. Absorption Spectra Visible Light Chlorophyll Carotenoids Phycocyanin Collectively 0 20 40 60 80 100 % Light Absorption 400 450 500 550 600 650 700 750 Wavelength (nanometers) 400 450 500 550 600 650 700 750
    21. 21. Overview of Photosynthesis Glucose O 2 Light-Dependent Reactions (in thylakoids) Light-Independent Reactions (in stroma) Depleted Carriers (ADP, NADP + ) Energized Carriers (ATP, NADPH) H 2 O CO 2
    22. 22. The Photosystems
    23. 23. Light-Dependent Reactions <ul><li>Steps of the light reactions: </li></ul><ul><li>Accessory pigments in Photosystems absorb light and pass energy to reaction centers containing chlorophyll </li></ul><ul><li>Reaction centers receive energized electrons… </li></ul>
    24. 24. Light-Dependent Reactions <ul><li>Energized electrons then passed down a series of electron carrier molecules ( Electron Transport Chain ) </li></ul><ul><li>Energy released from passed electrons used to synthesize ATP from ADP and phosphate </li></ul><ul><li>Energized electrons also used to make NADPH from NADP+ + H+ </li></ul>
    25. 25. Thylakoid Structure & Light-Dependent Reactions
    26. 26. Oxygen as a By-product
    27. 27. Chemiosmosis 1
    28. 28. Chemiosmosis 2
    29. 29. Light- In dependent Reactions <ul><li>NADPH and ATP from light-dependent reactions used to power glucose synthesis </li></ul><ul><li>Light not directly necessary for light-independent reactions if ATP & NADPH available </li></ul><ul><li>Light-independent reactions called the Calvin-Benson Cycle or C 3 Cycle </li></ul>
    30. 30. The C 3 Cycle <ul><li>6 CO 2 used to synthesize 1 glucose (C 6 H 12 O 6 ) </li></ul><ul><li>Carbon dioxide is captured and linked to ribulose bisphosphate (RuBP) </li></ul><ul><li>ATP and NADPH from light dependent reactions used to power C 3 reactions </li></ul>
    31. 31. C 3 Cycle Has Three Parts <ul><li>1. Carbon fixation (carbon capture) </li></ul><ul><ul><li>6 Ribulose bisphosphate (RuBP) molecules combine with 6CO 2 </li></ul></ul><ul><ul><li>Fixation step and subsequent reactions yield twelve 3-carbon phosphoglyceric acid (PGA) molecules… </li></ul></ul>
    32. 32. C 3 Cycle Has Three Parts <ul><li>2. Synthesis of Glyceraldehyde 3-Phosphate (G3P) </li></ul><ul><ul><li>Energy is donated by ATP and NADPH </li></ul></ul><ul><ul><li>Phosphoglyceric acid (PGA) molecules are converted into glyceraldehyde 3-Phophate (G3P) molecules … </li></ul></ul>
    33. 33. C 3 Cycle Has Three Parts <ul><li>3. Regeneration of Ribulose bis-phosphate (RuBP) </li></ul><ul><ul><li>10 of 12 G3P molecules converted into 6 RuBP molecules </li></ul></ul><ul><ul><li>2 of 12 G3P molecules used to synthesize 1 glucose </li></ul></ul><ul><ul><li>ATP energy used for these reactions </li></ul></ul>
    34. 34. The C 3 Cycle of Carbon Fixation …or… Dark Reactions …or… Light-Independent Reactions …or… Calvin Cycle …or… Calvin-Benson Cycle
    35. 35. Relationship Between Reactions <ul><li>The “photo” part of photosynthesis refers to the capture of light energy (light dependent reactions) </li></ul><ul><li>The “synthesis” part of photosynthesis refers to glucose synthesis (light- in dependent reactions) </li></ul>
    36. 36. Relationship Between Reactions <ul><li>Light dependent reactions produce ATP and NADPH which is used to drive light-independent reactions </li></ul><ul><li>Depleted carriers (ADP and NADP + ) return to light-dependent reactions for recharging </li></ul>
    37. 37. A Summary of Photosynthesis Light-dependent reactions occur in thylakoids Light- independent reactions (c 3 cycle) occur in stroma
    38. 38. Water, CO 2 , and the C 4 Pathway <ul><li>The ideal leaf: </li></ul><ul><ul><li>has large surface area to intercept sunlight </li></ul></ul><ul><ul><li>are porous to allow for CO 2 entry from air </li></ul></ul><ul><li>Problem: Substantial leaf porosity leads to substantial water evaporation, causing dehydration stress on the plant </li></ul><ul><li>Plants evolved waterproof coating and adjustable pores (stomata) for CO 2 entry </li></ul>
    39. 39. When Stomata Are Closed <ul><li>When stomata close, CO 2 levels drop and O 2 levels rise </li></ul><ul><li>Carbon fixing enzyme combines O 2 instead of CO 2 with RuBP (called photorespiration ) </li></ul><ul><li>Photorespiration: </li></ul><ul><ul><li>O 2 is used up as CO 2 is generated </li></ul></ul><ul><ul><li>No useful cellular energy made </li></ul></ul><ul><ul><li>No glucose produced </li></ul></ul><ul><ul><li>Photorespiration is unproductive and wasteful </li></ul></ul>
    40. 40. When Stomata Are Closed <ul><li>Hot, dry weather causes stomata to stay closed </li></ul><ul><li>Oxygen levels rise as carbon dioxide levels fall inside leaf </li></ul><ul><li>Photorespiration very common under such conditions </li></ul><ul><li>Plants may die from lack of glucose synthesis </li></ul>
    41. 41. C 4 Plants Reduce Photorespiration <ul><li>“C 4 plants” have chloroplasts in bundle sheath cells as well as mesophyll cells </li></ul><ul><ul><li>Bundle sheath cells surround vascular bundles deep within mesophyll </li></ul></ul><ul><ul><li>C 3 plants lack bundle sheath cell chloroplasts </li></ul></ul>
    42. 42. C 3 Plants & the Pathway C 3 plants use the C 3 pathway In a C 3 plant, most chloroplasts are in mesophyll cells.
    43. 43. C 3 Plants & the Pathway Much photorespiration occurs under hot, dry conditions
    44. 44. C 4 Plants & the C 4 Pathway C 4 plants use the C 4 pathway In a C 4 plant, both mesophyll & bundle-sheath cells contain chloroplasts.
    45. 45. C 4 Plants & the C 4 Pathway Almost no photorespiration occurs under hot, dry conditions. CO 2 is captured with a highly specific enzyme. Much glucose synthesis occurs. Mesophyll cell in a C 4 plant Bundle-sheath cell in a C 4 plant
    46. 46. The end

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