• 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
•Energy from food is
converted into high
energy bonds in ATP
•ADP + P + energy ATP
• 6 CO2 + 6 H2O + Light Energy
C6H12O6 + 6 O2
• Basis of most of the earth’s food
• Produces and maintains all of the
earth’s atmospheric oxygen
• Most oxygen produced in the
• Mostly chlorophyll a and chlorophyll b
• Accessory pigments:
• Each pigment absorbs a particular
wavelength of light in the visible
Reactants & Products
Pigments – protein molecules that
absorb specific colors of light.
• Most plants have
at least 3
• 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
• 12 H2O + Energy 6 O2 + 24 H+ +
24e• Requires light for the energy to split the
• 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
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 &
• Occurs in the
• Oxygen is released as
a waste product.
• NADPH – an energy
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
• Carbon Dioxide and
converted into ½ of a
glucose = PGAL
Calvin Cycle (Light-Independent Reaction) –
• CO2 is converted into
• Occurs in the Stroma.
• ATP and NADPH
provide the energy.
• PGAL = 3 carbon
sugar that is used to
make Glucose or other
Overview of the Dark Reactions
• Carbon dioxide is broken and “fixed” into
glucose or fructose molecules in the
• 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