Chloroplasts and Light Energy

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Chloroplasts and Light Energy
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Chloroplasts

• Belong to the class of organelles known as the
  plastids.
• They are the sites for photosynthesis in plant
  cells and some forms of eukaryotic algae.

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Chloroplast Parts

• Like mitochondria, they have two membranes.
• The interior space is filled with a protein-rich
  fluid called stroma.
• In the stroma are membrane-bound sacs called
  thylakoids.
• The inside of the thylakoid is known as the
  thylakoid lumen.

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Chloroplast Parts

• The thylakoids stack on top of one another. This
  stack of thylakoids is called a granum.
• Grana are linked to one another by unstacked
  thylakoids, which are called lamellae.

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Chloroplast Info

• The thylakoid membrane contains light gathering
  pigments and electron transport chains that are
  essential to photosynthesis.
• Chloroplasts contain their own DNA and ribosomes
  so they can reproduce independent of the cell.
• Excess glucose formed during photosynthesis is
  stored as starch inside the chloroplast.

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Chloroplasts
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Chloroplasts
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Photosynthesis

• It has three linked stages
• capturing light energy
• using the light energy to create ATP and NADPH
  (chemical energy)
• using the free energy from ATP and the reducing
  power of NADPH to synthesize organic compounds
  from atmospheric carbon.
• Stages 1 and 2 are better known as the light
  reactions while stage 3 is better known as the
  Calvin Cycle.

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Light

• Of all the light that hits the surface of the
  earth only about 5 is converted to organic
  compounds by photosynthesis.
• Light travels in wave packets called photons and
  light from the sun is a mixture of photons of
  different energies.

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Light

• Clusters of photosynthetic pigments, called
  photosystems, absorb particular wavelengths of
  light.
• Chlorophyll is located in these photosystems.

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Photosystems Preview
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Chlorophyll

• There are at least 4 different types of
  chlorophylls.
• Green plants contain chlorophyll a and
  chlorophyll b.
• Both these chlorophylls absorb blue light and red
  light the best and reflect green light, hence the
  green colour of chlorophyll.

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Chlorophyll

• Therefore we can assume that it is blue light and
  red light that is used in photosynthesis.
• Chlorophyll a is the only pigment that can
  transfer energy of light to the carbon fixation
  portion of photosynthesis (Calvin Cycle).
• Chlorophyll b is an accessory pigment that
  absorbs photons that chlorophyll a misses.

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Accessory Pigments

• There are other light absorbing pigments found in
  plants that can funnel light energy for
  photosynthesis.

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Carotenoids

• They are natural, organic pigments found in many
  plants as well as some species of algae, fungi
  and bacteria.
• They absorb high energy blue light that would
  normally damage chlorophyll and make it able to
  be used in photosynthesis. They reflect
  orange-yellow light.

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Carotenoids

• Some, like Beta-carotene, are important precursor
  molecules (Vitamin A) as well as anti-oxidants,
  so are good to have in ones diet!
• Xanthophylls are a yellow reflecting pigment from
  this family.
• Xanthophylls make chicken yolks yellow!