8.1 Photosynthesis uses light
energy to make food
I. The Structure of
Chloroplasts
A. Photosynthesis takes place in the
chloroplast
B. Chloroplasts contain compounds called
pigments that give leaves their color
(chlorophyll).
C. Leaves contain the most chloroplasts. (fig. 82)
D. Stoma are tiny pores that allow carbon
dioxide to enter and oxygen to leave the
plant cell.
Structure of chloroplast
E. Veins (xylem) carry CO2 and H2O from the
plants roots to the leaves and deliver
(phloem) organic compounds to other parts
of the plant.
F. The inner membrane of a chloroplast
encloses a thick fluid called stroma.
G. Suspended in the stroma are many disk
shaped sacs called thylakoids which are
arranged in stacks called grana.
H. These stacks organize the series of
reactions that make up photosynthesis.
Chloroplast
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1. In which part of a leaf are most chloroplasts located?
Cells containing chloroplasts are concentrated in the mesophyll.
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2. How is a thylakoid related to a granum?
A granum is a stack of thylakoids within a chloroplast.
II. Overview of Photosynthesis
A. In cellular respiration, electrons “fall” from
glucose to O2 to release energy.
B. In photosynthesis, electrons from water are
boosted “uphill” (potential) by the energy of
sunlight.
C. These excited electrons, along with carbon
dioxide and hydrogen ions to produce
C6H12O6 molecules
D. Photosynthesis occurs in two main steps:
Light and Calvin Cycle (Dark Reaction).
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1. For each of the two main stages of photosynthesis, identify the inputs.
Inputs of the light reactions are light and water, and ADP, P, and NADP+
from the Calvin cycle. Inputs of the Calvin cycle are CO2, and ATP and
NADPH from the light reactions.
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2. Identify the outputs for each stage, and tell how each is used.
Outputs of the light reactions are oxygen, which is released to the atmosphere, and ATP and
NADPH, which go into the Calvin cycle. Outputs of the Calvin cycle are ADP, P, and NADP+,
which go into the light reactions, and sugar, which is used by the plant.
III. The Light Reactions
A. Light Reactions convert the energy in
sunlight to chemical energy.
B. Chloroplasts use captured light energy to
remove electrons from H2O, splitting it into
oxygen and hydrogen ions.
C. The electrons and hydrogen ions are used to
make NADPH, which is an electron carrier.
D. Chloroplasts also use the captured light
energy to generate ATP.
E. 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
A. Calvin Cycle makes sugar from the atoms in
carbon dioxide plus the hydrogen ions and
high energy electrons carried in NADP
B. The ATP made in the light reactions provides
the energy to make sugar.
C. The Calvin cycle is sometimes referred to as
the “light-independent reactions” because it
does not require light energy to begin.
See Overview fig. 8-4
8.2 The light reaction convert
light energy to chemical
energy
I. Light Energy and Pigments
A. Light is a form of electromagnetic energy that
travels in waves and the distance between
adjacent waves is called a wavelength.
B. The range of wavelengths is called the
electromagnetic spectrum. (fig. 8-5
C. Visible light only makes up a small portion of
the electromagnetic spectrum.
II. Pigments and Color
A. A substances color is due to chemical
compounds called pigments.
B. Waves of light shining on a material can be
absorbed, transmitted or reflected
C. 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
A. Using a technique called
chromatography different pigments in
a leaf can be observed. (fig. 88-7)
B. Chlorophyll a absorbs mainly blueviolet light while chlorophyll b
absorbs mainly red light.
IV. Harvesting Light Energy
A. Within the thykaloid membrane, chlorophyll
and other molecules are arranged in clusters
called photosystems. (fig. 8-8)
B. Each photosystem contains a few hundred
pigment molecules, including chlorophyll a
and b as well as carotenoids.
C. Each time a pigment molecule absorbs light
energy electrons are raised from a “ground
state” to an “excited state”.
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1. What does a photosystem consist of?
clusters of chlorophyll and other molecules embedded in the thylakoid
membrane
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2. How are electrons in chlorophyll and other pigment molecules affected
by light striking the photosystem?
Electrons become “excited”—that is, they gain energy when the
photosystem absorbs sunlight.
Harvesting light energy
D. This electron “jumps” from molecule to
molecule until it arrives at the reaction
center.
E. The reaction center consists of
chlorophyll a and a primary electron
carrier. Other teams of molecules are
also used to make ATP and NADPH
V. Chemical Products of Light
Reactions
A. 2 photosystems are involved in the light
reactions.
B. The first photosystem traps light energy and
transfers the light-excited electrons to the
electron transport chain, this can be referred
to as the “water splitting photosystem”.
(figs.8-10,11)
Light reaction products
C. The second photosystem can be thought of
as the “NADPH- producing photosystem”
This system produces NADPH by transferring
excited electrons and hydrogen ions to NAD+
D. The light reactions convert light energy to the
chemical energy of ATP and NADPH, NO
SUGAR has been produced, which is the job
of the CALVIN CYCLE.
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1. What
happens to
water
molecules in
the first
photosystem
?
Water
molecules
are split
into H+
ions,
electrons,
and
oxygen.
2. What is the
overall
result of the
light
reactions?
Energy in
sunlight is
converted
to chemical
energy in
the form of
ATP and
NADPH.
8.3 Calvin Cycle makes sugar
from carbon dioxide
I. A Trip Around the Calvin
Cycle
A. The Calvin Cycle is the sugar factory
within the chloroplasts.
B. 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).
Calvin cycle
C. The inputs for the Calvin cycle are ATP, CO2
and NADPH. (from light reaction and air thus
no light)
D. The cycles output is an energy rich sugar
molecule called G3P which is not quite
glucose but is used as the raw material to
make glucose as the plant needs to.
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1. In what forms
does carbon
enter and exit
the Calvin cycle?
Carbon enters
the cycle in the
form of three
CO2 molecules
and exits as one
molecule of G3P.
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2. What is the source
of the energy-rich
ATP and NADPH
molecules used in
the cycle?
ATP and
NADPH are
produced
during the light
reactions.
II. Summary of Photosynthesis
A. The equation (unbalanced) for
photosynthesis is
Carbon Dioxide + Water --> Glucose +
Oxygen
CO2 +
H2O
-->
C6H12O6 + O2
B. The light reactions take place in the
thylakoid membranes and convert light
energy into chemical energy in the form of
ATP and NADPH. (fig. 8-14)
C. The light reactions use the reactant H2O
and release the product O2.
Summary of photosynthesis
D.The Calvin cycle takes place in the
stroma uses ATP and NADPH to
convert CO2 to C6H12O6.
E. Photosynthesis is the first step in the
flow of energy through an ecosystem
F. Photosynthesis is the ultimate source
of all the food that you eat and all the
oxygen that you breathe
8.4 Photosynthesis has a
global impact
I. The Carbon Cycle
A. The C cycle is the process by which carbon
moves from inorganic to organic
compounds and back.
B. Through photosynthesis, producers convert
inorganic CO2 to organic compounds (ie
sugar).
C. Cellular Respiration by both producers and
consumers return the CO2 to the
atmosphere.
Carbon Cycle
D. No other chemical process matches
the output of photosynthesis.
E. Earth’s plants and other
photosynthetic organisms make up
about 160 billion metric tons of organic
material per year.
II. Photosynthesis and Climate
A. One organism may either produce or use a
relatively small amount of CO2, the total
effect of all the organisms on Earth is very
large.
B. CO2 only makes up 0.03 percent of the
Earth’s atmosphere before this century
C. CO2 is one of many gases that traps heat
from the sun that would have otherwise
escape back into space, this is the
greenhouse effect.
Global climate
D. The greenhouse effect keeps the
average temperature on Earth about 10
degrees C warmer than it would be
otherwise
E. The amount of CO2 in the atmosphere
is rising.
Climate Change - 1896
Greenhouse effect: Swedish scientist Svante
Arrhenius theorizes that doubling the amount
of carbon dioxide in the atmosphere might
raise the Earth's temperature by 5 or 6
degrees Celsius. Arrhenius suspects that coal
and fossil fuels burned by industrialized
countries are adding to the levels of carbon
dioxide in the atmosphere. The greenhouse
effect is a natural phenomenon in which
gasses such as carbon dioxide trap the sun's
warmth.
Climate Change - 1982
Ice insight: Ice cores from the Greenland
ice sheet show dramatic temperature
oscillations in a single century from the
past, an extremely short period for
climate change. Scientists also report
strong evidence for global warming and
call 1981 the warmest year on record.
Climate Change - 1990
Sign here: The IPCC presents its First
Assessment Report, stating that human
activities are substantially increasing the
concentrations of greenhouse gases in the
atmosphere. Two years later, the United
States, along with more than 100 other
countries, sign the United Nations Framework
Convention on Climate Change in Rio de
Janeiro, Brazil. It recognizes the climate
system as a shared resource and launches
efforts to curb climate change.
Climate Change - 1997
Kyoto: The Kyoto Protocol is negotiated
to reduce greenhouse gas emissions
5.2 percent below 1990 levels by 2012.
The United States signs the treaty, but
never becomes a full-fledged participant
as the U.S. Senate agrees in advance
not to ratify the treaty, citing economic
concerns. President Bush will withdraw
the United States from the treaty in
2001.
Climate Change - 2001
Mercury rising: The U.S. National Academy of
Sciences publishes a report requested by
President Bush on the human role in climate
change. The panel declares "temperatures
are, in fact, rising" and human activity is the
likely culprit, although it does not define the
influence of natural climate variability.
Predictions of a 3 degree Celsius warming
are called "consistent" with climate science.
Climate Change - 2005
Kyoto: The Kyoto Protocol enters into force on
February 16. The treaty was ratified by more
than 140 countries. Concentration of carbon
dioxide now stands at 372 parts per million,
higher than at any time in at least the past
420,000 years, according to David King, chief
science adviser to the British government.
Bonus 1A
• Based on the cellular respiration
equation – solve the following:
• Under anaerobic conditions 4 glucose
will make how many molecules of
• Carbon dioxide?
• ATP?
• Water
Bonus 2
• Based on the photosynthesis equation –
solve the following:
• Under anaerobic conditions 4 glucose
will make how many molecules of
• oxygen?
• carbon dioxide?
• water?