Photosynthesis

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Photosynthesis
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Photosynthesis

• a metabolic pathway that converts light energy
  into chemical energy.
• is the process by which plants, some bacteria,
  and some protists use the energy from sunlight to
  produce sugar.

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Photosynthesis
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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

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Photosynthesis

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

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Chloroplasts containing chlorophyll.
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Chloroplast
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Chloroplast
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Chlorophyll
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Visible Spectrum
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Photosynthetic Pigments
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H2O CO2 ? C6H12O6 O2(water) (carbon
dioxide) (light) ? (sugar) (oxygen)
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Light-dependent Reactions

• Overview light energy is absorbed by
  chlorophyll molecules-this light energy excites
  electrons and boosts them to higher energy
  levels. They are trapped by electron acceptor
  molecules that are poised at the start of a
  neighboring transport system. The electrons
  fall to a lower energy state, releasing energy
  that is harnessed to make ATP

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Energy Shuttling

• Recall ATP cellular energy-nucleotide based
  molecule with 3 phosphate groups bonded to it,
  when removing the third phosphate group, lots of
  energy liberated superb molecule for shuttling
  energy around within cells.
• Other energy shuttles-coenzymes (nucleotide based
  molecules) move electrons and protons around
  within the cell
• NADP, NADPH NAD, NADP FAD, FADH2

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Light-dependent Reactions

• Photosystem light capturing unit, contains
  chlorophyll, the light capturing pigment
• Electron transport system sequence of electron
  carrier molecules that shuttle electrons, energy
  released to make ATP
• Electrons in chlorophyll must be replaced so that
  cycle may continue-these electrons come from
  water molecules, Oxygen is liberated from the
  light reactions
• Light reactions yield ATP and NADPH used to fuel
  the reactions of the Calvin cycle (light
  independent or dark reactions)

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Calvin Cycle (light independent or dark
reactions)

• ATP and NADPH generated in light reactions used
  to fuel the reactions which take CO2 and break it
  apart, then reassemble the carbons into glucose.
• Called carbon fixation taking carbon from an
  inorganic molecule (atmospheric CO2) and making
  an organic molecule out of it (glucose)
• Simplified version of how carbon and energy enter
  the food chain

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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 dont come to us
  the way our cells can use them

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The process of photosynthesis.

• Lets watch a short video. Click on the picture
  above.

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How Leaves Work