Photosynthesis
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All energy for the planet comes from
the sun
Photoautotrophs - organisms that can
convert light energy to chemical
energy
Process by which plants and other
Photosynthesis autotrophs convert the energy of
sunlight into sugars.
Requires sunlight, water, and carbon
dioxide
Occurs in the leaves of plants in
organelles called chloroplasts
Overall Equation:
6 CO2 + 6 H20  C6H12O6 +
62 O2
Most photosynthesis occurs in
palisade layer.
Leaf Structure
Gas exchange of CO2 and O2 occurs
at openings called stomata
surrounded by guard cells mostly
on the lower leaf surface.
(mesophyll)
(mesophyll)
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Thylakoids - thickened regions;
stack of thylakoids called a granum.
Chloroplast
Structure
Thylakoid membrane - Inner
membrane
The liquid surrounding the
thylakoids is the stroma.
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Stroma
Granum
Thylakoid
Thylakoid membrane
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Light
 Sunlight is “white” light— mix of
different wavelengths
 Energy from sunlight is captured
with pigments—primarily chlorophyll
 Chlorophyll A is the most important
photosynthetic pigment.
Pigments
Other pigments called antenna or
accessory pigments also present in leaf
Chlorophyll B
Carotenoids (orange / red)
Xanthophylls (yellow / brown)
These pigments embedded in the
membranes of the chloroplast in
groups called photosystems.
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The Chemical
Process of
Photosynthesis
Occurs in 2 main phases:
1. Light-dependent reactions
“photo” of photosynthesis
 Light absorbed by pigments
2. Light-independent reactions
(Calvin Cycle)
“synthesis” of photosynthesis
 Trapped energy from sun is
converted to chemical energy of
sugars
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 Occur on the thylakoid membranes
 Electron Transport Chain
 Photosystem I & Photosystem II
 Light and water required
Light-dependent
 Energy storage molecules formed:
Reactions
 ATP
 NADPH
 Oxygen gas is waste product
 From the splitting of the water
molecule
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Water
Oxygen
The Photosystems are imbedded in the thylakoid membrane
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 Occur in the stroma
 No light required
Light-independent
Reactions
(Calvin Cycle)
 Energy Storage Molecules Used:
ATP and NADPH
 power the production of glucose
 6 molecules of CO2 + 6 existing
5-carbon compounds will be
“fixed” into one 6-carbon sugar:
glucose
Reusable Molecules Produced:
 ADP
 NADP+
 Six 5-carbon molecules
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Carbon Dioxide
Sugars and
Carbohydrates
Interdependence of Reactions
Overall Equation: 6 CO2 + 6 H20  C6H12O6 +
Photosynthesis animation
6 O2