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Photosynthesis

Photosynthesis. Light Reactions Calvin Cycle. 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2. Photosynthesis. “ Construction by light” Basic Equation. Take home message: The atoms that make up the reactants are the EXACT SAME atoms that make up the products. Photosynthesis.

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Photosynthesis

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  1. Photosynthesis Light Reactions Calvin Cycle

  2. 6CO2 + 6H2O  C6H12O6 + 6O2 Photosynthesis • “ Construction by light” • Basic Equation

  3. Take home message: The atoms that make up the reactants are the EXACT SAME atoms that make up the products.

  4. Photosynthesis • Occurs in Producers or Autotrophs: (make their food) • Algae, Plants, some bacteria • uses SMALL portion of the sun’s energy  Visible Light

  5. Photosynthesis • Consumers or Heterotrophs can’t use the sun’s light to make food • Get glucose by eating other plants or animals which eat plants • Herbivores,Carnivores,Omnivores

  6. There are actually poems written about photosynthesis! http://www.pbs.org/wgbh/nova/nature/photosynthesis.html

  7. Structures for Photosynthesis Can all cells photosynthesize? - NO In plants, only: MESOPHYLL cells (found in the leaf) can do PS. ANIMATION!! http://dendro.cnre.vt.edu/forestbiology/photosynthesis.swf

  8. Structure of the leaf

  9. Photosynthesis – The Leaf • Body of Leaf • light absorption & CO2 diffusion • Veins – transport tissue • Xylem: H20 & minerals from roots to leaf • Phloem: newly made glucose to rest of plant

  10. Structures of the Leaf • Spongy Mesophyll • Middle layer made of cells loaded with chloroplasts • Spaces for CO2 /O2 exchange and water vapor • Epidermis – top and bottom of the leaf • Secretes a waxy cuticle

  11. Structures of the Leaf • Stoma • Openings on underside of leaf through which gases diffuse • Guard cells are located on either side and control whether stoma is open or closed

  12. Stomates

  13. Role of the Stomates • When open • Oxygen out • Transpiration: letting water vapor out • CO2 in • Stomates close when water is low • When there is enough H20: open during day, closed at night

  14. Role of the Stomates • Rate of photosynthesis depends on CO2 levels in leaf • Stomates closed no CO2  no PS

  15. Structure of a chloroplast:

  16. In the Chloroplasts • Pigments: molecules that absorb light • Main pigment is chlorophyll (green) • Found in thylakoid membrane • Light energy converted to Chemical energy • Chem. Energy stored as glucose and starch

  17. In the Chloroplasts • Different pigments absorb/reflect different wavelengths with in visible light spectrum • Why do we see green?

  18. In the Chloroplasts

  19. The key Players in PS • We already know: chlorophyll, CO2, water and light • New players: • Electrons • NADP+/NADPH: an electron carrier

  20. http://dendro.cnre.vt.edu/forestbiology/photosynthesis.swf ANIMATION!!!!

  21. Step one: Light Reactions – convert visible light into chemical energy • Photosystems are groups of pigments that absorb light energy • These groups of pigments are embedded in the thylakoid membrane

  22. Step one: Light Reactions – convert visible light into chemical energy • Light energy splits H20 freeing H+ (protons) and electrons • A Proton gradient is established to make ATP using ATP synthase • Electrons are given to NADP+ to make NADPH

  23. Step one: Light Reactions – convert visible light into chemical energy • ATP and NADPH provide energy for step two http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html • http://www.stolaf.edu/people/giannini/flashanimat/metabolism/photosynthesis.swf • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html#

  24. Step two: light independent • Calvin Cycle • Energy in NADPH and ATP is used to build 2 3-carbon sugars and then 1 glucose from CO2 • Energy is now stored in the sugars • If not needed, turned to starch

  25. Three stages in Calvin Cycle • Carbon Fixation • CO2 attaches to RuBP  2 molecules of 3-PGA • Chemical Reshuffling • 3-PGA  G3P • Reforming RuBP • For every 6 molecules of G3P, created, • One is used toward the creation of sugars • Five are converted back to RuBP

  26. Key things to know • What is the purpose of the light reactions • What are the reactants and the final products • What is the purpose of the Calvin Cycle? • What is/are the reactants and the final products? • Why is carbon fixation and why do we need different methods to fix carbon?

  27. After Photosynthesis • glucose can be used immediately • Broken down; mitochondria converts energy to ATP • Glucose can be stored for later • Linked together to make starch • Stored glucose/starch can become food for other organisms

  28. Carbon Fixation Alternatives • Used by plants in Hot, Dry Climates • Photorespiration • Occurs at high light intensities and temperatures > 30 C • Low CO2, and High O2  decrease in carbon fixation (use O2, lose CO2)- inefficent (low) production of sugars.

  29. Carbon Fixation Alternatives • C4 plants • Carbon fixed into 4-carbon compounds • Occurs during the day, but uses two types of cells (mesophyll and BSC) • “same time, different place” • CAM Pathway (another modification of C4 metabolism) • Stomates open at night, closed in the day • Within the same cells • Different time , same place

  30. C4 plants (25% of all PS on land) • high daytime temperatures • intense sunlight. • Crabgrass, corn (maize), sorghum, sugar cane • CAM - • high daytime temperatures • intense sunlight • low soil moisture. • Cacti, pineapple, sedums

  31. Why aren’t all plants C4? • More energy intensive with less productivity • CAM PLANTS GROW SLOWLY!!!! • WHY…need to make starch or malate, then break it down (PEP CARBOXYLASE) • C3 is EFFICIENT… • Actually, if C4 plants are given enough water…will revert to C3 (can do both)

  32. C4 Pathway • Examples: Sugar cane, Corn, Crabgrass • Stomata partially closed during the day • Lose less water than C3 plants, but produce same amount of CHO (water efficient, growth efficient) • Part of carbon fixation done in a “different” cell (CO2 is “concentrated in these cells to increase the likelihood of creating sugars, instead of photorespiration.

  33. CAM PATHWAY • Stomates open at night, closed in the day • Take in CO2 at night and fix it into organic compounds • Slow growth, but very water efficient

  34. Hmmm what about water plants?

  35. Hydrophytic leaves are adapted to an aquatic existence.   Note that the upper palisade mesophyll is well developed for photosynthesis while the lower portion of the mesophyll is very loosely arranged with considerable open space which helps the leaf float to the surface.  The loosely arranged tissue of the lower mesophyll is aerenchyma.  stoma are located in the upper epidermis.

  36. The pine leaf is well adapted to dry conditions with a thick epidermis with stoma recessed into the into the surface.  Beneath the epidermis is the thick walled cells of the hypodermis which helps reduce water evaporation from the leaf.  The pine leaf has an endodermis inside the mesophyll which is not seen in either of the other leaf types observed.

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