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Photosynthesis and Respiration

Photosynthesis and Respiration

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Photosynthesis and Respiration

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  1. Photosynthesis and Respiration

  2. Definitions • Photosynthesis • How a Plant Harnesses Light Energy to Make Chemical Energy • Respiration • Turning Chemical Energy into Fuel for Growth, Development and Reproduction

  3. Photosynthesis

  4. Leaves and Leaf Structure • The Raw Materials of Photosynthesis Enter the Cells of the Leaf • Water and Carbon Dioxide • The Products of Photosynthesis Leave the Leaf • Sugar and Oxygen

  5. Nature of Light • Visible Light Is only a Small Portion of the Electromagnetic Spectrum • p. 108, text • Plants Use Light Energy mostly in the Visible Light Range for PS

  6. Nature of Light • When Light Hits an Object, 3 Possibilities • Absorbed by Object • Reflected off Object • Transmitted through Object • Colors We See Are actually Light Reflected from an Object • Something that Appears Green Is Reflecting Green Light and either Absorbing or Transmitting the other Wavelengths • Plants Reflect Green, but Absorb other Wavelengths for Use in PS

  7. Nature of Light • Plant Color Can Be an Indicator of Plant Health • Satellite Imagery (Remote Sensing) Can Be Used to Indicate Crop Health • Measures some Visible Light but also Measures Infrared • Drought-Stressed Plants Give off more Infrared Wavelengths • Can Use this System to Indicate Weed Impact and other Factors

  8. Nature of Light • Red and Blue Wavelengths most Important for PS • Captured by Chloroplasts and Used to Initiate PS Reactions

  9. Photosynthetic Reactions • Photos (light) • Synthesis (to put together) • Light Energy to Chemical Energy • Life on Earth Depends on this Process • Supplies Our Oxygen

  10. Photosynthetic Reactions • Overall Equation • C = Carbon • O = Oxygen • H = Hydrogen

  11. Photosynthetic Reactions • Overall Equation • Carbon Dioxide Has 1 Carbon and 2 Oxygen Atoms, Arranged O=C=O in the Molecule of Carbon Dioxide • Water Has 2 Hydrogen and 1 Oxygen Atoms, Arranged H=O=H in the Water Molecule

  12. Photosynthetic Reactions • The Overall Equation for PS Is Deceptively Simple • In Fact, a Complex Set of Physical and Chemical Reactions must Occur in a Coordinated Manner for the Synthesis of Carbohydrates • To Produce a Sugar Molecule such as Sucrose, Plants Require nearly 30 Distinct Proteins that Work within a Complicated Membrane Structure

  13. Chlorophyll and Accessory Pigments • A Pigment Is any Substance that Absorbs Light • The Color of the Pigment Comes from the Wavelengths of Light Reflected • Chlorophyll, the Green Pigment Common to all Photosynthetic Cells, Absorbs all Wavelengths of Visible Light Except Green, which It Reflects to Be Detected by Our Eyes

  14. Chlorophyll and Accessory Pigments • Chlorophyll Is a Complex Molecule • Several Modifications of Chlorophyll Occur among Plants and other Photosynthetic Organisms • All Photosynthetic Organisms Have Chlorophyll a • Accessory Pigments Absorb Energy that Chlorophyll a Does not Absorb • Chlorophyll b • Xanthophylls • Carotenoids (Beta-Carotene)

  15. Chlorophyll and Accessory Pigments • If a Pigment Absorbs Light Energy, 1 of 3 Things Will Occur • Energy Is Dissipated as Heat • The Energy may Be Emitted Immediately as a Longer Wavelength (a Phenomenon Known as Fluorescence) • Energy may Trigger a Chemical Reaction, as in PS • Chlorophyll Triggers a Chemical Reaction when It Is Associated with Proteins Embedded in a Membrane (as in a Chloroplast)

  16. Chloroplasts • Organelles in a Plant Cell • Location of Photosynthesis

  17. Chloroplasts • Inside the Chloroplast • Intertwined and Stacked Network of more Membranes • Thylakoids • Wafer-Like Structures • Granum/Grana • Stack of Thylakoids • Stroma • Areas between Grana • Chloroplast Has 3 Membrane Systems, Forming 3 Compartments

  18. Chloroplasts • Photosynthesis Takes Place inside these Structures

  19. Photosynthesis Stages • 2-Stage Process • Light Reactions • Require Light to Occur • Involves the Actual Harnessing of Light Energy • Occur in\on the Grana • Dark Reactions • Do not Need Light to Occur • Involve the Creation of the Carbohydrates • Products of the Light Reaction Are Used to Form C-C Covalent Bonds of Carbohydrates • Occur in the Stroma

  20. Light Reactions • Electron Transfer • When Light Strikes Magnesium (Mg) Atom in Center of Chlorophyll Molecule, the Light Energy Excites a Mg Electron and It Leaves Orbit from the Mg Atom • The Electron Can Be Converted to Useful Chemical Energy

  21. Light Reactions • Photophosphorylation • The Excited Electron (plus Additional Light Energy) eventually Provides Energy so a Phosphate Group Can Be Added to a Compound Called Adenosine Diphosphate (ADP), Yielding Adenosine Triphosphate (ATP) • ATP Is an Important Stored Energy Molecule

  22. ATP • ATP = Adenosine - (PO4-) - (PO4-) - (PO42-) • 3 Phosphate Groups Stuck off the End of an Adenosine Molecule • Fairly Simple Compound Containing Nitrogen • The String of 3 Phosphate Groups Is Held Together by Covalent Bonds • All Macromolecules Are Held Together by Covalent Bonds • For some Reason, Phosphate Groups in a String Need a Really, Really Strong Bond to Hold Them Together • So the Ones within the String Are Extremely Strong • Think of the Bond Like a Rope in a Tug-of-War with 2 People Pulling on the Rope in Opposite Directions • If someone Comes along and Cuts the Rope the 2 People Will Go Flying • They Go Flying off because Lots of Energy Was Being Stored in the Rope and the Energy Was Released as the People Fell • When the Bond that Attaches 1 of the Phosphate Groups onto ATP Is Broken, It Becomes ADP • Adenosine - (PO4-) - (PO42-)      +     (PO42-)      +     Energy

  23. Light Reactions • Photolysis (Hill Reaction) • The 2 Water Molecules Are Split into Hydrogen and Oxygen • The Hydrogen Is Attached to a Molecule Called Nicotinamide Adenine Dinucleotide Phosphate (NADP) • Produces NADPH2 • The Oxygen Is Given off as Oxygen Gas • 2 H20 + NADP + light  NADPH2 + O2

  24. Light Reactions • ATP and NADPH2 Are Common Energy-Carrying Molecules in all Plant and Animal Cells • ATP Gives up the Phosphate Group when It Is Involved in a Chemical Reaction • This Gives off a Lot of Energy which Helps the Needed Reaction Occur • Same Thing Happens when NADPH2 Gives off the Hydrogen Atoms as Part of a Reaction • It Provides Energy to Drive that Reaction • ATP and NADPH2 Are Renewable or Recyclable Energy Sources

  25. Dark Reactions • ‘Calvin Cycle’ • ‘Carbon Reactions Pathway’ • Do not Require Light Energy to Occur • Do Require Energy Captured by Light Reactions

  26. Dark Reactions • Occur at same Time as Light Reactions • Cease Soon if Light Energy Is not Available to Make Light Reaction Products • Exception: some Xerophytes

  27. Dark Reactions • 2 Main Steps • Carbon Dioxide Fixation • Sugar Formation • Occur in the Stroma of the Chloroplasts

  28. Carbon Dioxide Fixation • ‘Carbon Dioxide Assimilation’ • CO2 Is Incorporated into a 3-Carbon or 4-Carbon Chain • C3 Plants • C4 Plants

  29. Carbon Dioxide Fixation • C3 Plants • Most Plants Use an Enzyme Called RuBP Carboxylase (RuBisCo) to Carry out the CO2 Fixation • Enzymes Are Natural Proteins that Help Catalyze/Carry out Reactions • Rubisco Is the most Abundant Enzyme on Earth! • This Occurs in the Mesophyll Cells • Palisade or Spongy • Creates a 3-Carbon Product Ready for Sugar Formation • Called C3 Plants because the 1st Stable Carbon Chain Made from CO2 Has 3 Carbons • C3 Crops • Wheat, Soybeans, Cotton, Tobacco, Small Grains, Legumes, Tomatoes, Potatoes, Peppers, Cucurbits,

  30. Carbon Dioxide Fixation • C4 Plants • ‘Hatch-Slack Pathway’ • Process of CO2 Fixation for many Plants of Dry or Tropical Origins • Plants Use a Different Enzyme Called PEP in the Mesophyll Cells for CO2 Fixation • PEP Carboxylase Has a much Higher Affinity for CO2 than Does Rubisco • At Low CO2 Pressures, Rubisco Doesn’t Distinguish Well between O2 and CO2 so Stomata usually Have to Be Wide Open for PS to Occur • Creates a 4-Carbon Product

  31. Carbon Dioxide Fixation • C4 Plants • This 4-Carbon Chain Is then Transported into Bundle Sheath Cells where the CO2 Is Released and then Immediately Fixed by Rubisco as Part of the C3 Cycle • Bundle Sheath Cells Are Specialized Cells that Surround the Vascular Bundles in the Leaves • Same Fixation with Rubisco as in C3 Plants but Occurs in the Bundle Sheath Cells, not Mesophyll Cells,

  32. Carbon Dioxide Fixation • Transport of CO2 to the Mesophyll Cells Allows the C4 Plants to Build up a Higher Concentration of CO2 in the Bundle Sheath Cells than what Is Normally Found in the Mesophyll Cells of C3 or C4 Plants

  33. Carbon Dioxide Fixation • 1st Part of Calvin Cycle Occurs in Bundle Sheath Cells of C4 Plants and in Mesophyll Cells of C3 Plants

  34. PEP Carboxylase vs. Rubisco • PEP Carboxylase Works Well at Warm Temperatures but not Optimally at Cool Temps • This Is the Reason why C4 Grasses Are Referred to as Warm Season Grasses, and Why They Don’t Compete Well with C3 Grasses at Cooler Temps • C4 Grasses Have an Edge in Dry Warm Sites or Open Sunny Sites as They Can Keep Leaf Stomata Closed during Mid-Day and Extract every Last CO2 Molecule in the Leaf • In Contrast, C3 Grasses that Keep Stomata Closed in Dry Sunny Sites Undergo High Amounts of Respiration

  35. Carbon Dioxide Fixation • Both Types of Plants Use Energy from ATP and NADPH2 to Carry out the Reactions • The Energy from ATP Is Given by ATP Giving up Its 3rd Phosphorus • ATP → ADP + P • The Energy from NADPH2 Is Given by NADPH2 Giving up Its Hydrogens • NADPH2→ NADP + H2

  36. Sugar Formation • Carbon Chain Formed in step 1 Is Converted to Glucose • C6H12O6 • Overall PS Reactions and Energy Transfers Can Be Seen in Text

  37. Photosynthesis Logistics • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Carbon Dioxide Source • CO2 Enters Leaves through Stomata by Diffusion • Passive Process • Dissolves in Water Inside the Plant to Become the Bicarbonate Ion (HCO3-)

  38. Photosynthesis Logistics • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Water Source • Water Enters the Plant through the Roots • Moves up through Plants • Some Passive Movement • Active Process (Requires Chemical Energy to Occur) during some Parts of the Journey

  39. Photosynthesis Logistics • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Oxygen Output • Fate of Oxygen Produced by PS • Diffuse out through Stomata • Be used in Respiration or other Reactions • Only about 40% of Oxygen Produced Is Used by the Plant, so Plants Are a Net Oxygen Producer

  40. Photosynthesis Logistics • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Water Output • Fate of Water Produced by PS • Used in other Reactions or Plant Transport • Diffuses as Water Vapor out of Leaf through Stomata imagecollection.html

  41. Photosynthesis Logistics • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Sugar/Glucose Output • Fate of Glucose Produced by PS • Converted to Sucrose • Main Plant Sugar Used by Plants for Growth and Reproduction • Common Table Sugar • Water Soluble and Readily Transported to Sinks • Converted to Starch or other Storage Carbs • Starch Is a Long-Chain Polymer of many Glucose Molecules Linked Together • Water-Soluble to Be Able to Be Mobilized Later by Plants if Needed • Common Form of Stored Carbohydrates • Mainly Starch: White Potato and Sweet Potato Tubers, Seed Cotyledons, Endosperm

  42. Photosynthesis Logistics • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Sugar/Glucose Output • Fate of Glucose Produced by PS • Converted to Cellulose or other Structural Carbohydrate • Long-Chain Polymer of many Glucose Molecules Linked Together • Linked with Different Bond than Starch, so Cellulose Is not Water-Soluble • Formed by Cellulose and Related Compounds • Cell Walls • Plant Fibers (Cotton, Hemp, Jute) • Wood (Lignin is the main Structural Carbohydrate in Wood)

  43. Factors Affecting Photosynthesis • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Availability of CO2 • CO2 Supply Diminishes if Stomates Close • Air Movement Replaces CO2 Taken up by Plants • On Still Days within Crop Leaf Canopy • CO2 Levels may Drop Below Optimum, Slowing PS Slightly

  44. Factors Affecting Photosynthesis • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Availability of CO2 • Normal [CO2] Is 400 ppm (0.04%) • Increasing [CO2] can Increase Plant Photosynthetic Rates • Occurring due to Environmental Changes • Artificial Enhancement usually not Practical in Field Production • Has Been Used Effectively in some Greenhouse Production

  45. Factors Affecting Photosynthesis • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Availability of Water • Water (almost always) Is not a Limiting Factor for PS • So Little Is actually Used (Less than 1% of Water Absorbed) and Plants Are Made up of so much Water • Water Stress that Causes Stomata to Close can Slow or Stop PS due to Lack of CO2

  46. Factors Affecting Photosynthesis • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Light Quality (Color) • Chlorophyll Absorbs Light in Red (660 nm) and Blue (450 nm) Wavelengths • These Are the Photosynthetic Wavelengths of Light • Called Photosynthetically Active Radiation (PAR)

  47. Factors Affecting Photosynthesis • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Light Duration (Photoperiod) • Plants Need Sufficient Length of Light Period to Produce enough Carbs for Normal Growth • Longest Days in Northern Hemisphere Occur in June • December in Southern Hemisphere

  48. Factors Affecting Photosynthesis • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Light Intensity (Brightness) • As Light Intensity Increases, PS Rates Increase • Up to a Certain Level of Intensity • Light Saturation Point • PS Reaches Its Maximum Point • Increasing Light Intensity no Longer Increases PS Rate

  49. Factors Affecting Photosynthesis • 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O • Leaf Chlorophyll Content • Pigment that Captures Light Energy and Begins the Transformation of that Energy to Chemical Energy • Located in Chloroplasts • About 20 to 100 Chloroplasts/Mesophyll Cell in Leaves

  50. Factors Affecting Photosynthesis • Leaf Chlorophyll Content • Chlorosis is Yellowing of Leaf from Lack of Chlorophyll • If Chlorophyll Is Reduced, PS Will Be Reduced • Causes of Chlorosis • Nutrient Deficiencies • N and Mg Are Parts of the Chlorophyll Molecule • K Needed for Enzyme Activation in Production of Chlorophyll • Any other Nutrient Deficiencies that Cause Chlorosis also Reduce PS • Diseases