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Photosynthesis and Cellular Respiration

Photosynthesis and Cellular Respiration. How do cells obtain organic compounds for energy?. Heterotrophs : Cannot make their own food Autotrophs : Can make their own food Photoautotrophs : Use energy from the sun (photosynthesis) to produce organic compounds (glucose)

vernon-rowland
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Photosynthesis and Cellular Respiration

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  1. Photosynthesis and Cellular Respiration

  2. How do cells obtain organic compounds for energy? • Heterotrophs: Cannot make their own food • Autotrophs: Can make their own food • Photoautotrophs: Use energy from the sun (photosynthesis) to produce organic compounds (glucose) • Plants, algae and some bacteria • Chemoautotrophs: Use energy stored in inorganic compounds (chemosynthesis) to produce organic compounds • Some bacteria found at the hydrothermal vents of the seafloor

  3. Photosynthesis • Method of converting light energy from the sun into chemical energy that cells can use • Divided into the light-dependent and light-independent reactions • Photosynthesis takes place in chloroplasts • The parts of a chloroplast are as follows: • Thylakoids- disk-shaped structures that contain the pigment chlorophyll (absorbs the sunlight) • Grana- A stack of thylakoids • Stroma- Liquid between grana

  4. Draw a Chloroplast

  5. Overall Photosynthesis Reaction 6CO2 + 6 H2O + light energy → C6H12O6 + 6O2 • On the left of the arrow are the reactants (the components that “react” together). • On the right of the arrow are the products. • Identify how a plant obtains the reactants.

  6. Light-dependent Reactions • Chlorophyll (in thylakoids) absorbs the light energy • Plants have 2 types: Chlorophyll A and Chlorophyll B • Water molecules are split apart producing H and O2 • Electrons flow throughout the thylakoid membrane (electron transport chain) • Energy compounds ATP and NADPH are produced

  7. Light-independent Reactions (Dark Reactions) • Occur in the stroma • ATP and NADPH from the light reactions are used to fuel the break down of CO2 and the reassembling of the atoms to produce glucose. • This reassembling is called “carbon fixation”. • Carbon fixation occurs in a series of reactions called the Calvin Cycle.

  8. Harvesting Chemical Energy • So we see how energy enters food chains (via autotrophs) we can look at how organisms use that energy to fuel their bodies. • 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

  9. 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

  10. 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

  11. 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

  12. 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, final steps in these pathways serve ONLY to regenerate NAD+ so it can return to pick up more electrons and hydrogens in glycolysis. • End products such as ethanol and CO2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells)

  13. 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

  14. 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

  15. 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

  16. 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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