Photosynthesis

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Photosynthesis

• Honors Biology

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Overview of Photosynthesis

• What is Photosynthesis?
• 6 CO2 6 H2O ? C6H12O6 6 O2
• light energy
• Photosynthesis is the process of converting light
  energy into food energy (glucose, chemical energy
  stored in chemical bonds).
• Photosynthesis carried out by plants and algae.

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Structures of Photosynthesis

• Cross-section of a Leaf
• 6 CO2 6 H2O ? C6H12O6 6 O2
• light energy

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Structures of Photosynthesis

• Cross-section of a Leaf
• Palisade Mesophyll
• Spongy Mesophyll
• Guard cell
• Stomata
• Epidermis
• Cuticle
• Vein

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What is Solar Energy and Visible Light?

• Visible Light is made of photons that travel at
  various wavelengths and frequencies.
• Photons (packets of energy) are formed when an
  electron is energized and moves to a higher
  energy level, which is unstable. When the
  electron falls back to its original energy level,
  then a photon is released that travels at a
  particular wavelength.
• The longer the wavelength, the lower the energy.
  The shorter the wavelength, the higher the energy.

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What is Solar Energy and Visible Light?

• Visible light is only one form of energy in the
  Electromagnetic Spectrum.
• Different colors of light have different
  wavelengths.
• Which color of light contains the most energy?
  Least energy?

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How do Plants Capture Solar Energy for use in
Photosynthesis?

• Each plant cell contains 40-50 chloroplasts.
• Chloroplasts contain pigments that either absorb
  or reflect different wavelengths of visible
  light. Absorbed wavelengths are used for
  photosynthesis.
• Each thylakoid membrane contains 250-400
  chlorophyll pigments

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Review Parts of a Chloroplast
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Plant Pigments

• Reaction Center Pigment Chlorophyll a
• Antennae/Accessory Pigments Chlorophyll b,
  carotenoids, phycobilins (red algae)
• What is the absorption spectra for each pigment?
  (spectrophotometer)
• Chlorophyll a and b red, orange, yellow, blue,
  and violet (reflects green)
• Carotenoids violet, blue, and green (reflects
  red, orange, and yellow)
• Phycobilins violet, blue, green, yellow, and
  orange (reflects red)

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Photosynthesis is Composed of 2 Reactions

• What are the two main reactions of
  Photosynthesis? Reactants? Products? Where
  located?
• Light-Dependent reactions Energy capturing
  reactions, captures solar energy and traps it as
  ATP and NADPH. Occurs in Thylakoid membranes.
• Light-Independent reactions Synthesis
  reactions, uses the ATP and NADPH and captured
  CO2 to make glucose. Occurs in the Stroma.

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What factors affect the rate of photosynthesis?

• Amount of Visible light and CO2
• Amount of H2O, Minerals, Temperature

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Light-Dependent Reactions

• 1. Photosystem II absorbs light energy and
  transfers
• an excited electron to the Primary electron
  acceptor.

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Light-Dependent Reactions

• 2. Primary Electron Acceptor molecule transfers
  high energy electrons to the Electron Transport
  System, which establishes a H ion gradient
  across the thylakoid membrane.

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Light-Dependent Reactions

• 3. Energy from the Electron Transport Chain
  establishing a H ion gradient is used for
  Chemiosmotic Phosphorylation production of ATP.
  (Photophosphorylation)

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Light-Dependent Reactions

• 4. The electron from the Electron Transport
  System is accepted by the reaction center
  chlorophyll of Photosystem I.
• 5. The Electron Acceptor molecule of Photosystem
  I sends its electron to ultimately form NADPH.

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Light-Dependent Reactions Reviewed

• Where does the light reaction take place?
• At the thylakoid membrane
• What are the inputs to the light reactions?
• Light energy, water
• What are the products of the light reaction?
• ATP, NADPH, and O2

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Light-Independent Reactions (Calvin Cycle)

• Synthesis reactions that occur in the stroma
• CO2 ATP NADPH ? Glucose
• Carbon dioxide comes into the leaf via stomata
• ATP and NADPH from the Light reactions
• No light required but typically occurs during the
  day

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Three stages of the Calvin Cycle

• 1. Carbon Dioxide Fixation
• 2. Carbon Dioxide Reduction
• 3. Regeneration of RuBP

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Review Photosyntheis

• What are the two reactions of photosynthesis?
• How are the light reactions connected to the
  Calvin cycle?

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Three Modes of Photosynthesis

• C3 Plants
• C4 Plants
• CAM Plants
• The pathways of photosynthesis discussed in this
  presentation are for C3 plants.
• Examples wheat, rice, oats
• Optimum temperature 15-25C

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C4 Plants

• Mesophyll cells fix CO2 into a C4 molecule
  (oxaloacetate) during the day.
• Uses PEPCase enzyme instead of Rubisco to fix CO2
• C4 molecule pumped to Bundle sheath cells where
  Calvin Cycle occurs.
• Examples sugar cane, corn, bermuda grass,
  crabgrass
• Net photosynthetic rate is greater than C3
  plants.
• More heat tolerant, optimum temperature 30-40C

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CAM Plants

• Like C3 plants, Mesophyll cells fix CO2 in the
  Calvin Cycle, but it occurs at night. Stomata
  only open at night to bring in CO2 and reduce
  water loss.
• Like C4 plants, CO2 is fixed into a C4 molecule
  and then stored in large vacuoles in mesophyll
  cells to be used the following day when ATP and
  NADPH are available from the light reactions.
• Uses PEPCase enzyme instead of Rubisco to fix CO2
• Examples succulents like cacti that live in
  deserts (CAM Crassulacean-acid metabolism)
• Low photosynthetic rate, variable
• Most heat tolerant, optimum temperature 35C

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Review C3, C4, and CAM plants

• What are the differences between C3, C4, and CAM
  plants?

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References

• http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
  BioBookPS.html