Exercise 6: Photosynthesis

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Exercise 6Photosynthesis
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Questions that will be addressed

• Where does the carbon that organic molecules are
  made of come from?
• Where does the energy that drives the synthesis
  of organic molecules come from?

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The answers vary, depending on the organism

• Autotrophs Self-nourishing
• Photoautotrophs Carbon source is CO2 from the
  air and sunlight is the energy source that drives
  synthesis.
• Heterotrophs Feed on autotrophs.

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Photoautotrophs

• Plants, some bacteria, and many protistans are
  photoautotrophs.
• Photoautotrophs synthesize organic molecules from
  CO2 by a process called Photosynthesis.
• Photosynthesis energy form the sun is used to
  drive synthesis.

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Overview of Photosynthesis
Glucose
Sucrose, Starch, or Cellulose
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Photosynthesis Occurs in Two Stages

• 1. Light-Dependent Reactions Split water and
  generate ATP and NADPH
• Occur in the Thylakoid Membrane of Chloroplast
• 2. Light-Independent Reactions Use the ATP and
  NADPH generated in the Light-Dependent reactions
  to make Glucose.
• Occur in the Stroma of Chloroplast

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The Light-Dependent Reactions

• Photoautotrophs use pigments to absorb sunlight
  energy.
• This energy is then used to drive photosynthesis.

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Properties of Light contd

• Visible light is in the l range of 400-700 nm.
• People and other organisms see the different ls
  as different colors.

Wavelength of light (nanometers)
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Light as particles

• The energy of light is absorbed as if it is
  organized into packets. These packets are called
  Photons.
• Each type of photon has a fixed amount of energy
  characterized by its wavelength.
• Pigments are molecules that absorb photons.
• Most pigments only absorb some wavelengths of
  light and transmit (reflect) others. The
  wavelengths that are transmitted, determine what
  color an object appears.
• A pigment that absorbs all wavelengths of visible
  light appears black.
• A pigment that reflects all wavelengths of
  visible light appear white.

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Pigments

• Chlorophylls are the primary pigments in most
  photoautotrophs.
• Chlorophyll a mostly absorb red and blue light.
• Chlorophyll b absorbs blue and red-orange
  light.
• Carotenoids, Xanthophylls, anthocyanins, and
  phycobilins are accessory pigments found in
  photoautotrophs.
• They absorb wavelengths that chlorophylls miss,
  blue-violet and blue-green. They reflect red,
  orange, and yellow.

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Absorption Spectrum
beta-carotene
phycoerythrin (a phycobilin)
percent of wavelengths absorbed
percent of wavelengths absorbed
chlorophyll a
chlorophyll b
wavelengths (nanometers)
wavelengths (nanometers)
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Absorption Spectrum
(combined absorption efficiency across entire
visible spectrum)
chlorophyll b
chlorophyll a
chlorophyll a
carotenoids
chlorophyll b
phycoerythrin (a phycobilin)
Phycocyanin (a phycobilin)
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Plant PigmentPaper Chromatography

• Chromatography is the separation of molecules in
  a mixture based on their solubility in a
  particular solvent and their interaction with the
  chromatography matrix.
• Pigments
• Chlorophyll a, Chlorophyll b, Beta-carotenes, and
  Xanthophylls.
• Solvent Petroleum Ether and Acetone are
  non-polar solvents.
• The most non-polar pigments will travel further
  up the paper while the polar pigments will not
  travel as far.

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Plant Pigment Paper Chromatography
Beta-Carotene
Distance pigment moved
Ratio Factor (Rf)
Distance solvent moved
Xanthophylls
Chlorophyll a
Chlorophyll b
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Measuring Photosynthesis in Elodea

• We will measure photosynthesis in Elodea under
  different light conditions.
• White light Oxygen Production
• No light Oxygen Consumption
• Green light Oxygen Production

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White Light
Net Photosynthesis
Respiration
Photosynthesis
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Absorption Spectrum
(combined absorption efficiency across entire
visible spectrum)
chlorophyll b
chlorophyll a
chlorophyll a
carotenoids
chlorophyll b
phycoerythrin (a phycobilin)
Phycocyanin (a phycobilin)
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No Light
X
X
Respiration
Photosynthesis
Net Photosynthesis Respiration Gross
Photosynthesis
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Green Light
Net Photosynthesis
X
X
Respiration
Photosynthesis
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Absorption Spectrum
(combined absorption efficiency across entire
visible spectrum)
chlorophyll b
chlorophyll a
chlorophyll a
carotenoids
chlorophyll b
phycoerythrin (a phycobilin)
Phycocyanin (a phycobilin)
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No Green Light
X
X
Respiration
Photosynthesis
Net Photosynthesis Respiration Gross
Photosynthesis
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CO2 Uptake
H2O CO2 HCO2 -OH
Carbonic Acid