Photosynthesis

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Photosynthesis

• Why Is It Important?

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What is Photosynthesis?

• Definition the process by which autotrophs
  convert sunlight into a usable (stored) form of
  energy (sugar/food).

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Light Energy Harvested by Autotrophs
6 CO2 6 H2O light energy ? C6H12O6 6 O2
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Background

• Light travels in waves
• These waves carry energy (hot pavement)
• Photosynthesizers use this energy to make food.
• Organisms depend on three types of energy
• Light
• Chemical (ATP)
• Heat

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Visible Spectrum of Light

• What we can see
• (380 to 750 nm)
• A leaf look green because of chlorophyll, the
  dominant pigment
• Absorbs red and blue light
• Reflects green light

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Leaf Structure
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Location of Photosynthesis

• Occurs in the chloroplasts (plant organelle)
  which are in the leaf of plants.
• These chloroplasts contain pigments like
  chlorophyll

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Parts of Chloroplast

• Thylakoid
• Internal membrane system
• Location of step one (light rxns.)
• Resemble stacks of quarters
• Contains chlorophyll pigment
• Grana
• Stacks of thylakoids
• Resembles a stack of quarters
• Stroma
• Gel-like substance surrounding thylakoids
• Location of step two of photosynthesis (calvin
  cycle)

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Chlorophyll
Chlorophyll the main pigment in chloroplast that
absorbs light for photosynthesis
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Label the Parts of Chloroplast
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The Actual Process

• CO2 H2O sunlight? C6H12O6 (sugar) O2

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ATP Adenosine Triphosphate
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Two Steps (an overview)

• 1. Light Dependent Reactions need the sun
• 2. Calvin Cycle do not need the sun
• (aka light independent reactions)

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Light Dependent Rxns. (part 1 of Photosynthesis)

• Step 1
• Light hits chlorophyll molecules
  (photosystemsclusters of chlorophyll molecules
  and other pigments)

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Light Dependent Rxns. (part 1 of Photosynthesis)

• Step 2
• Photosystems lose electrons
• Water is split into oxygen and hydrogen
• This replaces the electrons lost from the
  chlorophyll

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Light Dependent Rxns. (part 1 of Photosynthesis)

• Step 3
• Electrons fall through the electron transport
  chain.

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Light Dependent Rxns. (part 1 of Photosynthesis)

• ATP (chemical energy) is made when H (from
  water) is pumped across the thylakoid membrane
• This will be used to provide energy for step 2

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Light Dependent Rxns. (part 1 of Photosynthesis)

• Step 4
• These electrons are picked up by an electron
  acceptor (NADP) forming NADPH (an energy
  molecule)
• This will also be used to provide energy for step
  2

Animation Light Rxn. Overview
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Light Reactions
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The steps of the Light Rxns.
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Calvin Cycle (part 2 of photosynthesis)

• Step 1
• Carbon Fixation CO2 is attached to an RuBP
  (intermediate 5-C molecule).
• CO2 comes from the
• atmosphere
• New 6-C molecule is
• unstable

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Calvin Cycle Cont.

• Step 2
• Reduction to G3P (another intermediate)
• ATP and NADPH provide energy for this step to
  occur
• Some carbon leaves cycle to make sugar (glucose)

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Calvin Cycle Cont.

• Step 3
• Recycling of RuBP to be used again.
• Rest of carbon from G3P
• makes RuBP again
• Energy (ATP) is needed for this to occur

Overall products of the Calvin Cycle Sugar
(food)
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Fate of Sugars

• Used immediately for food.
• Stored as starch.
• Building material (cellulose)

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View the Calvin cycle
Overall products of the Calvin Cycle Sugar
(food)
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Label the Calvin cycle
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A quick Overview
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Photosynthesis, Keystone-style

• A process in which solar radiation is chemically
  captured by chlorophyll molecules through a set
  of controlled chemical reactions resulting in the
  potential chemical energy in the bonds of
  carbohydrate molecules.
• What???
• Break it down!