Concept 8.1:
Photosynthesis uses light
energy to make food
I. The structure of Chloroplasts
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The structure where photosynthesis
takes place is the chloroplast.
Chloroplasts contain compounds called
pigment that give leaves their color.
Leaves contain the most chloroplasts.
There are tiny pores called stoma that
allows carbon dioxide to enter and
oxygen to leave the cell.
I. The structure of Chloroplasts
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Veins carry CO2 and H2O from the
plants roots to the leaves and deliver
organic compounds to other parts of the
plant.
The inner membrane of a chloroplast
encloses a thick fluid called stroma.
Suspended in the stroma are many disk
shaped sacs called thylakoids which are
arranged in stacks called grana.
These stacks organize the series of
reactions that make up photosynthesis.
Photosynthesis
II. Overview of Photosynthesis
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In cellular respiration, electrons “fall”
from glucose to O2 to release energy.
In photosynthesis, electrons from water
are boosted “uphill” by the energy of
sunlight.
III. The Light Reactions
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These excited electrons, along with carbon
dioxide and hydrogen ions produce C6H12O6
molecules
Photosynthesis occurs in two main steps: Light
Reaction and Calvin Cycle (Dark Reaction).
The Light Reactions…con’t
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Light Reactions convert the energy in sunlight
to chemical energy.
Chloroplasts use captured light energy to
remove electrons from H2O, splitting it into
oxygen and hydrogen ions.
The electrons and hydrogen ions are used to
make NADPH, which is an electron carrier
Chloroplasts also use the captured light energy
to generate ATP.
The overall result of the light reactions is the
conversion of light energy to chemical energy
stored in NADPH and ATP.
IV. The Calvin Cycle
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Calvin Cycle makes sugar from the
atoms in carbon dioxide plus the
hydrogen ions and high energy electrons
carried in NADPH.
The ATP made in the light reactions
provides the energy to make sugar.
The Calvin Cycle is sometimes referred
to as the “light-independent reactions”
because it does not require light energy
to begin.
Concept 8.2 The Light Reactions
Convert Light Energy to
Chemical Energy
I. Light Energy and Pigments
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Light is a form of energy that travels in waves
and the distance between adjacent waves is
called a wavelength.
The range of wavelengths is called the
electromagnetic spectrum.
Visible light only makes up a small portion of
the electromagnetic spectrum.
II. Pigments and Color
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A substances color is due to chemical
compounds called pigments.
Waves of light shining on a material can be
absorbed, transmitted or reflected.
Leaves absorb blue-violet and red-orange light
very well but either reflect or transmit green
light and that is why leaves look green
III. Identifying Chloroplast
Pigments
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Using a technique called
chromotography different pigments
in a leaf can be observed.
Chlorophyll a absorbs mainly blueviolet light while chlorophyll b
absorbs mainly red light.
IV. Harvesting Light Energy
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Within the thylakoid membrane, chlorophyll and
other molecules are arranged in clusters called
photosystems.
Each photosystem contains a few hundred
pigment molecules, including chlorophyll a and
b as well as carotenoids.
Each time a pigment molecule absorbs light
energy electrons are raised from a “ground
state” to an “excited state”
Concept 8.3: The Calvin
Cycle makes sugar from
carbon dioxide
A Trip around the Calvin Cycle
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The Calvin Cycle is the sugar factory within the
chloroplasts.
The starting material for the Calvin Cycle is
regenerated each time the process occurs, the
starting material is called RuBP, (a sugar with
five carbons)
Inputs for the Calvin Cycle are ATP, CO2 and
NADPH. (from light reaction and air thus no light)
The cycles output is an energy rich sugar
molecule called G3P which is not quite like
glucose but it used as the raw material to make
glucose as the plant needs to.
A Trip around the Calvin Cycle
II. Summary of Photosynthesis
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The overall equation for photosynthesis is:
6 CO2 + 6 H2O  C6H12O6 + 6 O2
Carbon dioxide
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+
water

Glucose
+
Oxygen
The light reaction take place in the thylakoid
membranes and convert light energy into
chemical energy in the form of ATP and NADPH.
The light reactions use the reactant H2O and
release the product O2.
The Calvin Cycle takes place in the stroma and
uses ATP and NADPH to convert CO2 to C6H12O6.
Summary of Photosynthesis
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Photosynthesis is the first step in the flow of
energy through an ecosystem.
Photosynthesis is the ultimate source of all the
food that you eat and all the oxygen that you
breathe.
Concept 8.4:
Photosynthesis has a
global impact
I. The Carbon Cycle
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The Carbon Cycle is the process by which carbon
moves from inorganic to organic compounds and
back.
Through photosynthesis, producers convert
inorganic CO2 to organic compounds. (ex: sugar)
Cellular Respiration by both producers and
consumers return the CO2 to the atmosphere.
No other chemical process matches the output of
photosynthesis.
Earth’s plants and other photosynthetic
organisms make up about 160 billion metric tons
of organic material per year.
II. Photosynthesis and Global Climate
One organism may either produce or use a
relatively small amount of CO2, the total
effect of all the organisms on Earth has a
very large effect.
 CO2 only made up 0.03% of the Earth’s
atmosphere before this century.
 CO2 traps heat from the sun that would
have otherwise escaped back into space,
this property is known as the Greenhouse
Effect.
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Greenhouse Effect
Photosynthesis and Global Climate
 The
greenhouse effect keeps the
average temperature on Earth about
10 degrees warmer than it would be
otherwise.
 The amount of CO2 in the
atmosphere is rising with no end in
sight.