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Photosynthesis
Historical discoveries
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Van Helmont’s experiment – In the 1600’s van
Helmont wanted to determine if plants grew by taking
material out of the soil…
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Preistley’s experiment- In the 1700’s Priestley
wanted to determine what made the “carbo” part
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The result- NO
Proved that water was responsible for the “hydrate” part of
carbohydrate.
The result – carbon dioxide
Experiment with plant growing in jar provided oxygen for
flame.
Ingenhousz experiment – Later Ingenhousz showed
that the effect observed by Priestly only occurred
when a plant was exposed to sunlight.
The Photosynthesis Equation
6 CO2 + 6 H2O
sunlight
C6H12O6 + 6 O2
Additional requirements
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Aside from water, sunlight, and carbon
dioxide, plants also need chlorophyll.
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Chlorophyll is a pigment , which is a substance
that absorbs and reflects light (which is the
reason plants look green)
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Because light is a form of energy, any compound
that absorbs light also absorbs energy from that
light. In plants most of the energy is immediately
transferred into electrons in the chlorophyll
molecule.
Inside a Chloroplast
Photosystem – Clusters of pigments including chlorophyll in
the thylakoid membrane
Electron carriers
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NADP+  NADPH
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NADP+ accepts and holds 2 electrons and a
hydrogen ion
NADPH carries these electrons to places in the cell
where molecules like glucose are built.
The reactions
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Light-dependent reactions
 The Calvin Cycle
Light-Dependent Reactions
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Use light and water to release oxygen and
make ATP and NADPH (photolysis)
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Therefore ADP and NADP+ are required
ATP synthase – molecule found in the cell
membrane that lets H+ ions pass through thus
making ATP
Takes place in the thylakoid
The Calvin Cycle
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Uses ATP and NADPH and CO2 to produce
high energy sugars (glucose)
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ATP and NADPH can’t store energy for more than
a couple of minutes
Takes place in the stroma
2 Cycles of Photosynthesis
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Light Dependent
Reactions
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Occur in the
thylakoid
Use light and water
to make oxygen,
ATP and NADPH
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Electron carriers
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Calvin Cycle
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Occurs in the stroma
Use carbon dioxide,
ATP and NADPH to
make glucose
vocabulary
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Pigment- molecule that absorbs and reflects light
Chlorophyll- principal pigment of plants and other
photosynthetic organisms; captures light energy
Photosynthesis- process by which plants and some
other organisms use light energy to convert water and
carbon dioxide into oxygen and high-energy
carbohydrates such as glucose
NADP+ - one of the carrier molecules that transfers
high-energy electrons from chlorophyll to other
molecules.
Calvin Cycle- reactions of photosynthesis in which
energy from ATP and NADPH is used to build
glucose; occurs in the stroma
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Light-dependent reactions – reactions of
photosynthesis that use energy from light to produce
ATP and NADPH; occurs in the thylakoid
Stroma- region outside the thylakoid membranes in
chloroplasts
Thylakoid- sac-like membranes that absorb light in
chloroplasts
ATP synthase- a large protein that allows H+ ions to
pass through the cell membrane to produce ATP
Photosystem- clusters of pigment in the thylakoid that
absorb light to begin photosynthesis
Page 107
Adenosine Triphosphate
Adenosine Diphosphate
Fig. 7.4
Page 131
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