Photosynthesis

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Photosynthesis

• Chapter 10

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Photosynthesis Overview
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Chloroplasts The Sites of Photosynthesis in
Plants

• The leaves of plants
• Are the major sites of photosynthesis

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Stages of Photosynthesis

• Light Reactions
• Happens in thylakoid
• Solar energy is converted to chemical energy in
  the form of NADPH and some ATP (photophosphorylati
  on)
• Electrons are extracted from H2O ? H and O2
• 2. Calvin cycle
• Happens in stroma
• ATP and NADPH are used to
• Reduce CO2 to C6H12O6 (Carbon fixation)

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Light

• Visible light can be broken up into the spectrum
• Each color of the spectrum is a different
  wavelength

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Pigments

• Pigments are substances that absorb visible light
  of a specific wavelength
• Plants have two main pigments
• chlorophyll a
• chlorophyll b
• Carotenoids are accessory pigmentsless important

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• What type of light do plants absorb best?
• What does this tell you about pigment color and
  absorption?

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• A spectrophotometer measures the ability of a
  pigment to absorb light

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• What wavelengths of light work best for
  photosynthesis?
• How do you know?
• Why do they work best?

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How does chlorophyll capture light energy?

• When chlorophyll absorbs light it causes one of
  the electrons in the molecule to be
  excitedboosted to an orbital of higher energy
  level.
• Excited state is unstable, so the excited
  electrons quickly drop back down to ground state.
• Energy is then released as the electron falls
  back down (usually as heat)
• How is this related to why the hood of a car is
  so hot when its out in the sun?

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The Light Reactions

• Happens in thylakoid
• Solar energy is converted to chemical energy in
  the form of NADPH and some ATP (photophosphorylati
  on)
• Electrons are extracted from H2O ? H and O2

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Photosystemscapturing light energy

• Other pigment and Chlorophyll molecules work
  together to combine and use their captured energy
  from light
• A variety of pigment molecules are located in
  light harvesting complexes
• The pigment molecules pass the energy from light
  to each other and on to the
• reaction center
• Chlorophyll a molecules
• Primary electron acceptor

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WHERE?
Where did the electrons come from?
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LightReactions

• Photon of light hits pigment molecule
• Energy is relayed through pigments to chlorphyll
  A (P680)
• Energy excites electrons of chlorophyll a
• Electrons are replaced by extracting them from
  water. H2O ? 2H O
• Excited electron is then passed down an electron
  transport chain
• Energy released is use to make ATP

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Continued

• At the next photosystem the same thing happens
• But excited electrons are used/passed to NADP to
  make NADPH
• What do you think NADPH does??

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