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Energy Fixation by Autotrophs

Energy Fixation by Autotrophs. Solar energy converted to chemical energy CO 2 converted to Carbohydrate Solar energy + 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2. Photosynthesis:. Happy Rays of Sunshine. You need to know this. O 2 (to air). CO 2 (from air). C 6 H 12 O 6. H 2 O.

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Energy Fixation by Autotrophs

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  1. Energy Fixation by Autotrophs

  2. Solar energy converted to chemical energy CO2 converted to Carbohydrate Solar energy + 6CO2 + 6H2O→ C6H12O6 + 6O2 Photosynthesis: Happy Rays of Sunshine You need to know this O2 (to air) CO2 (from air) C6H12O6 H2O

  3. Radiant Energy • Photosynthesis converts solar energy into the chemical energy of a carbohydrate by two sets of reactions: • Solar energy + 6CO2 + 6H2O→ C6H12O6 + 6O2 Reduced Oxidized Carbohydrate (glucose) Electrons from H2O are energized by the sun.

  4. Oxidation-Reduction • Oxidation is the loss of electrons (energy) and reduction is the gain of electrons (energy). • In covalent rxn’s, oxidation also refers to the loss of hydrogen atoms, and reduction refers to the gain of hydrogen atoms.

  5. Chloroplast structure Double membrane Thylakoids are interconnected Chlorophyll and other pigments are found in the thylakoids

  6. Photosynthesis Overview • Composed of light-dependent and light-independent reactions • Light-dependent reactions (Thylakoids) • Capture solar energy and excite electrons • Water molecule is split and electrons and H+ enter the electron transport system • O2, NADPH, and ATP are produced • Light-independent reactions (Stroma) • CO2 is reduced to a carbohydrate • NADPH and ATP are consumed

  7. Light-dependent Reactions Solar energy is used excite electrons (increases potential energy). ADP and NADP+ are reduced to ATP and NADPH. ATP and NADPH are then used to power the light-independent reactions. Water is split  H+, e-, and O2 *Considered an electron donor*

  8. Light-independent Reactions • Calvin Cycle – three stages • CO2 fixation, CO2 reduction, RuBP regeneration • Reactions require energy, which is supplied by ATP and NADPH

  9. Light-independent Reactions-Calvin Cycle Fixation of CO2 From light-dependant reactions From light-dependant reactions

  10. Photosynthesis in Chloroplast Light Independent ReactionsLight Dependant Reactions CO2 H2O Solar Energy Calvin Cycle Electron Pathways RuBP PGAL ATPO2 NADPH Glucose Aerobic Cellular Respiration in Mitochondria makes new ATP

  11. Overview of Cellular Respiration • Cellular respiration is the step-wise release of energy from molecules (usually carbohydrates) used to synthesize ATP molecules. • This is an aerobic process that requires oxygen (O2) and gives off carbon dioxide (CO2), and involves the complete breakdown of glucose to carbon dioxide and water.

  12. Mitochondrion structure Mitochondria are bounded by a double membrane surrounding fluid-filled matrix. The inner membranes of mitochondria are cristae. The matrix contains enzymes that break down carbohydrates and the cristae house protein complexes that produce ATP.

  13. Drives ATP synthesis Oxidation of glucose is an exergonic reaction (releases energy) which drives ATP synthesis - an endergonic reaction (energy is required).

  14. Phases of Complete Glucose Breakdown • Glycolysis - yields 2 ATP; occurs in cytoplasm • Citric acid cycle (yields 2 ATP) and Electron transport system (yields 32-34 ATP); occur in the mitochondria • Net ATP produced from respiration: 36-38

  15. Overview of Glycolysis Glucose (6-C sugar) 2 ADP 6-C sugar diphosphate 3-C sugar-phosphate 3-C sugar-phosphate 2 ATP 2 ATP 2 NADH 2 NADH 3-C pyruvate 3-C pyruvate

  16. Fermentation inputs and outputs per glucose molecule Inputs: glucose 2 ATP 4 ADP + 2 P Outputs: 2 lactate or 2 alcohol and 2 CO2 2 ADP 2 ATP (net) Pyruvate (Oxygen present) (Oxygen not present) Cellular Respiration Fermentation

  17. 2 NAD+ 2 NADH + H 2Pyruvate + 2CoA 2 Acetyl-CoA + 2CO2 Pyruvate oxidation: if oxygen is present Pyruvate is converted to a C2acetyl group attached to coenzyme A (CoA), and CO2is released. This occurs in the cytoplasm if oxygen is present.

  18. Krebs Cycle • The Krebs cycle is a cyclical metabolic pathway located in the matrix of the mitochondria. • At the start of the citric acid cycle, CoA carries the C2 acetyl group to join a C4 molecule, and C6citrate results.

  19. Citric acid (Kreb’s) cycle: Substrate-level phosphorylation results in a gain of one ATP per every turn of the cycle; it turns twice per glucose. Produces CO2, ATP and NADH

  20. Electron Transport Chain • The electron transport chain located in the cristae of mitochondria is a series of protein carriers • Electrons carried by NADH and FADH2 enter the electron transport chain. • As a pair of electrons is passed from carrier to carrier, energy is released and is used to form ATP molecules by oxidative phosphorylation.

  21. Overview of the electron transport chain Oxygen receives energy-spent electrons at the end of the electron transport system. Next, oxygen combines with hydrogen, and water forms: ½ O2 + 2 e- + 2 H+→ H2O

  22. Photosynthesis is the process that produces energy rich organic molecules from energy deficient inorganic materials. Photosynthetic organisms are thus termed producers – they produce food for themselves as well as consumer organisms! Plants and consumers harvest energy from photosynthetic products through cellular respiration.

  23. Primary Production • Primary production - the synthesis of organic matter by autotrophs • Always measured as a rate per unit of time • Sugar cane farmers  kg/ha/yr cane production • To accumulate organic matter, photosynthesis must be greater than respiration • Compensation point – when photosynthesis = respiration • No growth / no reproduction

  24. Two Measures of Production = = NPP = GPP - Respiration You need to know this

  25. Worldwide Gross Primary Production

  26. Primary Productivity Heat Energy Chemical Energy (ATP) Solar Energy CO2 Respiration Photosynthesis C6H12O6 O2 Available to Consumers Biomass (g/m2/yr) GPP NPP

  27. Measuring Primary Production: Terrestrial • Primary production measured as a rate per unit time • Can measure CO2 uptake rate during the day = net production • CO2 released at night = respiration

  28. Energetic Equivalents 12H20 + 6CO2 + 2966kj + solar energy  C6H12O6 + 6O2 + 6H20 • Absorption of 6 moles of CO2 indicates that 2966kj of energy has been absorbed • This gives us a relationship between carbonaccumulated and energy gained • We can determine the amount of carbon in a plant be measuring the amount of energy in that plant

  29. Harvest Method B = B2 – B1 • Whole plant, aerial production, or root production: • Two possible losses must be recognized L = biomass losses by death of plants or plant parts G = biomass losses to consumer organisms • With those values: NPP = B + L + G

  30. Aquatic Primary Production • The most important primary producers in aquatic systems are phytoplankton • Single cell plants suspended in the water column • Estimate primary production by measuring gas-exchange using light bottle dark bottle • Light bottle determines oxygen produced by photosynthesis • Dark bottle measures oxygen consumed by respiration

  31. Phytoplankton:

  32. Measure initial oxygen concentration in both bottles Place bottles in water for a specific period during the day Measure final oxygen concentration in both bottles Light – Dark Bottle LBI = initial O2 in the light bottle DBI = initial O2 in the dark bottle LBF = final O2 in the light bottle DBF = final O2 in the dark bottle GPP = LBF – DBF (Total oxygen produced) NPP = LBF – LBI (Oxygen increase) Respiration = DBI – DBF(Oxygen decrease)

  33. GPP = LBF – DBF (Total oxygen produced) NPP = LBF – LBI (Oxygen increase) Respiration = DBI – DBF(Oxygen decrease) LBI = 5.3 DBI = 5.3 LBF = 6.8 DBF = 4.2; 1 hr GPP = LBF – DBF = 6.8 – 4.2 = 2.6 mg/L/hr NPP = LBF – LBI = 6.8 – 5.3 = 1.5 mg/L/hr Respiration = DBI –DBF= 5.3 – 4.2 = 1.1 mg/L/hr NPP = GPP – Respiration = 2.6 – 1.1 = 1.5 mg/L/hr

  34. What Does Production Actually Mean?? • More carbon fixed from the atmosphere = more food available • The greater the productivity, the greater the biomass of heterotrophs that can be supported

  35. How to Estimate Carbon Produced • 1 mg/L O2 = 0.375 g Carbon • GPP = 2.6 mg O2/L/hr * 0.375 = 0.975 mg C/L/hr • NPP = 1.5 mg O2/L/hr * 0.375 = 0.563 mg C/L/hr • For this example, 0.563 mg of carbon per liter of water per hour are added as biomass to the system

  36. Estuaries Swamps and marshes Tropical rain forest Temperate forest Northern coniferous forest (taiga) Savanna Agricultural land Woodland and shrubland Temperate grassland Lakes and streams Continental shelf Open ocean Tundra (arctic and alpine) Desert scrub Extreme desert 800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600 Average net primary productivity (kcal/m2/yr) Net Primary Production (measure of produced energy)

  37. Estimated NPP

  38. Ocean Productivity • On a per square meter basis the oceans are about as productive as the arctic tundra • Sometimes called a biological desert • However, because the ocean’s make up 71% of the Earth’s surface, they account for 46% of total productivity

  39. Energy fixed by primary production* Energy input per unit area per unit time Efficiency of GPP = X 100 Photosynthetic Efficiency • Percentage of received solar energy a plant uses: *Calculate number of carbon atoms from plant weight. Can then calculate the amount of energy required to build the plant.

  40. = 0.42% 20,991 kJ/m2/yr gross primary production 4,973,604 kJ incident sunlight Efficiency of GPP = X 100 Efficiency of Lake Mendota, Wisconsin

  41. dldt = kl Limiting Factors – Aquatic Communities • Depth of light penetration determines the photic zone: Where: l = amount of solar radiation (joules per m2 per unit of time) t = depth k = extinction coefficient • Typically, more than half of the solar radiation is absorbed in the first meter of water:

  42. Attenuation of Solar Radiation Coastal seawater ~k=0.3 Mississippi River? -Turbulence Pure water Oceanic seawater

  43. Lake Classification Based on Production • Eutrophic – high production but little light penetration • Oligotrophic – low production but high light penetration

  44. Rate of Photosynthesis Measured as grams of carbon fixed per m2 Eutrophic Intermediate Oligotrophic Note the scale

  45. Marine Communities North Pacific Gyre Euphotic Zone – the surface down to 1% light level Nutrient Limited?

  46. Why are the Ocean’s so Unproductive? P – High; N – Low Nitrogen, not phosphorous, is limiting Surprising because of the ability of cyanobacteria to fix atmospheric nitrogen?

  47. What else? • Top down control – Predation (by herbivores) is actually limiting the phytoplankton population • Nutrients  phytoplankton  zooplankton  fish • Herbivory limits phytoplankton • Bottom up control – Some other nutrient than nitrogen or phosphorous may be limiting • Nutrients  phytoplankton  zooplankton  fish • Nutrients limit phytoplankton

  48. Sargasso Sea • Found not to be N or P limited, but Iron limited

  49. Why Iron • Cyanobacteria fix atmospheric nitrogen to a form available to phytoplankton • Iron is necessary for this process: Iron  cyanobacteria  N fixation  phytoplankton

  50. Nutrient Addition:303 studies combined Silica important when community dominated by diatoms

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