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PHOTOSYNTHESIS
Today’s Objectives
• Given information and/or diagrams
on the process of photosynthesis,
write and/or identify the equation,
raw materials, sites, products,
factors affecting the process, and
the role of chlorophyll in the light
and dark reactions.
ATP: The Cell’s Currency
•Adenosine Triphosphate
•Energy from food is
converted into high
energy bonds in ATP
•ADP + P + energy  ATP
Photosynthesis
• 6 CO2 + 6 H2O + Light Energy 
C6H12O6 + 6 O2
• Basis of most of the earth’s food
chains
• Produces and maintains all of the
earth’s atmospheric oxygen
• Most oxygen produced in the
oceans
Photosynthetic Pigments
• Mostly chlorophyll a and chlorophyll b
• Accessory pigments:
• Carotenoids
• Anthocyanins
• Each pigment absorbs a particular
wavelength of light in the visible
spectrum
ELECTROMAGNETIC SPECTRUM
Photosynthesis:
Reactants & Products
Chloroplast Structure
Pigment Absorption
Pigments – protein molecules that
absorb specific colors of light.
• Most plants have
at least 3
pigments:
• 1. Chlorophyll A
• 2. Chlorophyll B
• 3. Carotenoids
* Why do leaves change color in the fall?
Overview of Photosynthesis
Step I: Light Reactions
• Involves the splitting of water
(photolysis)
• 12 H2O + Energy  6 O2 + 24 H+ +
24e• Requires light for the energy to split the
water molecule
• Also forms a highly energetic compound,
adenosine triphosphate (ATP)
Overview of the Light Reactions
• Think of the light reaction, as a
process by which organisms
"capture and store" radiant energy
as they produce oxygen gas. This
energy is stored in the form of
chemical bonds of compounds
such as NADPH and ATP.
Light Reaction = Electron Transport
When Sunlight is absorbed by Photosystem II, electrons
are “kicked out”.
Water is “split” to replace lost electrons.
Electrons are passed along a chain of molecules to
Photosystem I.
Energy from moving electrons is used to pump protons
inside the thylakoid.
Light Reaction - Analogy
Light-Dependent Reaction – Summary
• Water and Light are
converted into ATP &
NADPH.
• Occurs in the
Thylakoid Membrane.
• Oxygen is released as
a waste product.
• NADPH – an energy
(electron) carrying
molecule
Step II: Dark Reactions
• Does not require light but can happen at
any time of day.
• The energy from NADPH and ATP is used
for carbon fixation
• 6 CO2 + 24 H+ + 24 e- ------>
C6H12O6 + 6 H2O
• The chemical bonds present in glucose
also contain a considerable amount of
stored (potential) energy.
Dark Reaction – Calvin Cycle
• Energy stored from the
light reaction (ATP &
NADPH) is used to
power the production
of sugar.
• Carbon Dioxide and
Hydrogen are
converted into ½ of a
glucose = PGAL
C
A
L
V
I
N
C
Y
C
L
E
Calvin Cycle (Light-Independent Reaction) –
Summary
• CO2 is converted into
carbohydrate (PGAL).
• Occurs in the Stroma.
• ATP and NADPH
provide the energy.
• PGAL = 3 carbon
sugar that is used to
make Glucose or other
carbohydrates.
Overview of the Dark Reactions
• Carbon dioxide is broken and “fixed” into
glucose or fructose molecules in the
CALVIN CYCLE!!!!
• Glucose subunits can make cellulose or
other polysaccharides, such as fruit sugars.
• The carbon skeleton in glucose also helps
to synthesize other important biochemical
compounds such as, lipids, amino acids,
and nucleic acids.
Diagram of Photosynthesis