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Photosynthesis and Cellular Respiration

Photosynthesis and Cellular Respiration. Do Now – 1/4. Where does energy start in all ecosystems? What is the 3 step energy pathway?. Outline. I. Photosynthesis A. Introduction B. Reactions II. Cellular Respiration A. Introduction B. Reactions. Photosynthesis.

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Photosynthesis and Cellular Respiration

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  1. Photosynthesis and Cellular Respiration

  2. Do Now – 1/4 • Where does energy start in all ecosystems? • What is the 3 step energy pathway?

  3. Outline I. Photosynthesis A. Introduction B. Reactions II. Cellular Respiration A. Introduction B. Reactions

  4. Photosynthesis • Method of converting sun energy into chemical energy usable by cells • Autotrophs: self feeders, organisms capable of making their own food • Photoautotrophs: use sun energy e.g. plants photosynthesis-makes organic compounds (glucose) from light • Chemoautotrophs: use chemical energy e.g. bacteria that use sulfide or methane chemosynthesis-makes organic compounds from chemical energy contained in sulfide or methane

  5. Photosynthesis • Photosynthesis takes place in specialized structures inside plant cells called chloroplasts • Light absorbing pigment molecules e.g. chlorophyll

  6. Overall Reaction • 6CO2 + 12 H2O + light energy → C6H12O6 + 6O2+ 6H2O • energy is required to drive this reaction

  7. Light-dependent Reactions • light energy is absorbed by chlorophyll molecules- • this light energy excites electrons and boosts them to higher energy levels. • The electrons “fall” to a lower energy state, releasing energy that is harnessed to make ATP

  8. ETC: Light-dependent Reactions • Photosystem: light capturing unit, contains chlorophyll, the light capturing pigment • Electron transport chain (ETC): sequence of electron carrier molecules that shuttle electrons, energy released to make ATP • Light reactions yield ATP and NADPH used to fuel the reactions of the Calvin cycle (light independent or dark reactions)

  9. Calvin Cycle (light independent or “dark” reactions) • ATP and NADPH generated in light reactions used to fuel the reactions • Called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose)

  10. Checking for Understanding 1. What is the equation for photosynthesis? 2. Photosynthesis turns light energy to what kind of energy? 3. What are the two steps of photosynthesis? 4. Which reaction is light dependent? 5. What are the roles of pigments in photosynthesis? 6. Do all organisms perform photosynthesis? 7. What organelle performs photosynthesis?

  11. Harvesting Chemical Energy • Plants and animals both use products of photosynthesis (glucose) for metabolic fuel • Heterotrophs: must take in energy from outside sources, cannot make their own e.g. animals • When we take in glucose (or other carbs), proteins, and fats-these foods don’t come to us the way our cells can use them

  12. Cellular Respiration Overview • Transformation of chemical energy in food into chemical energy cells can use: ATP • These reactions proceed the same way in plants and animals. Process is called cellular respiration • Overall Reaction: • C6H12O6 + 6O2→ 6CO2 + 6H2O

  13. Cellular Respiration Overview • Breakdown of glucose begins in the cytoplasm: the liquid matrix inside the cell • At this point life diverges into two forms and two pathways • Anaerobic cellular respiration (aka fermentation) • Aerobic cellular respiration

  14. C.R. Reactions • Glycolysis • Series of reactions which break the 6-carbon glucose molecule down into two 3-carbon molecules called pyruvate • Process is an ancient one-all organisms from simple bacteria to humans perform it the same way • Yields 2 ATP molecules for every one glucose molecule broken down • Yields 2 NADH per glucose molecule

  15. Anaerobic Cellular Respiration • Some organisms thrive in environments with little or no oxygen • Marshes, bogs, gut of animals, sewage treatment ponds • No oxygen used= ‘an’aerobic • Results in no more ATP, only performs glycolysis. • End products such as ethanol and CO2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells)

  16. Aerobic Cellular Respiration • Oxygen required=aerobic • 2 more sets of reactions which occur in a specialized structure within the cell called the mitochondria • 1. Kreb’s Cycle • 2. Electron Transport Chain

  17. Kreb’s Cycle • Completes the breakdown of glucose • Takes the pyruvate (3-carbons) and breaks it down, the carbon and oxygen atoms end up in CO2 and H2O • Hydrogens and electrons are stripped and loaded onto NAD+ and FAD to produce NADH and FADH2 • Production of only 2 more ATP but loads up the coenzymes with H+ and electrons which move to the 3rd stage

  18. Electron Transport Chain • Electron carriers loaded with electrons and protons from the Kreb’s cycle move to this chain-like a series of steps (staircase). • As electrons drop down stairs, energy released to form a total of 32 ATP • Oxygen waits at bottom of staircase, picks up electrons and protons and in doing so becomes water

  19. Energy Tally • 36 ATP for aerobic vs. 2 ATP for anaerobic • Glycolysis 2 ATP • Kreb’s 2 ATP • Electron Transport 32 ATP 36 ATP • Anaerobic organisms can’t be too energetic but are important for global recycling of carbon

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