PHOTOSYNTHESIS

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PHOTOSYNTHESIS
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Photosynthesis

• A carbon dioxide (CO2) requiring process that
  uses light energy (photons) and water (H2O) to
  produce (glucose).
• 6CO2 6H2O ? C6H12O6 6O2

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Question

• Where does photosynthesis take place?

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Plants

• Autotrophs Produce their own carbohydrates.
• Photosynthetic Surface
• 1. Leaves
• a. stomate
• b. Chloroplast

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Stomates

• Pores in a plants cuticle (outer leaf surface)
  through which water and gases are exchanged
  between the plant and the atmosphere.

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Plant Cell in Leaf

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Chloroplast

• Organelle where photosynthesis takes place.

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Question

• Why are plants green?

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Chlorophyll Molecules

• Chlorophyll pigments harvest energy (photons) by
  absorbing certain wavelengths (blue-420-470 nm
  and orangered-620-670 nm are most important).
• Plants are green because the green wavelength is
  reflected, not absorbed.

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Wavelength of Light (nm)

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Electromagnetic Spectrum
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Absorption of Chlorophyll
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Question

• During the fall, what causes the leaves to change
  colors?

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Fall Colors

• In addition to the chlorophyll pigments, there
  are other pigments present.
• During the fall, the green chlorophyll pigments
  are greatly reduced (lower light intensity)
  revealing the other pigments.
• Carotenes are pigments that are orange.
• Xanthophylls are pigments that are yellow.

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Breakdown of Photosynthesis

• Two main parts (reactions).
• 1. Light Reactions
• Converts energy from solar power (photons) into
  the form of ATP and NADPH.

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Breakdown of Photosynthesis

• Dark Reaction Calvin Cycle
• -Process of Carbon Fixation
• -Uses Carbon Dioxide from the environment and
  energy (ATP and NADPH) from light rxn to make
  sugar (glucose).

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Light Reaction Summary

• Light energy excites electrons in chlorophyll
• Light energy breaks down water
• ATP and NADPH is formed
• Oxygen is released
• Occurs in the Grana

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Electron Flow
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Electron Flow cont.

• ADP ? ATP
• NADP 2H ?? NADPH
• Oxygen comes from the splitting of H2O, not CO2
• H2O ? 1/2 O2 2H

(Reduced)
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Dark Rxn/Calvin Cycle

• Carbon Fixation
• Uses ATP and NADPH from light rxn.
• Uses CO2 absorbed through the stomates of the
  leaves.
• Produces PGAL which combines to form glucose it
  takes 6 CO2 and uses 18 ATP and 12 NADPH.

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Photosynthesis

H2O
CO2
Energy
ATP and NADPH2
Which splits water
Light is Adsorbed By Chlorophyll
Calvin Cycle
ADP NADP
Chloroplast
Used Energy is recycled.
O2
C6H12O6

Light Reaction
Dark Reaction
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Water
Light
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Chloroplast