PHOTOSYNTHESIS
Review Your Understanding
AP Biology
Begin Presentation
Overview
• This interactive presentation will review
the major concepts involved in
photosynthesis allowing you to focus on
areas that are least clear.
• At the end of the presentation there will be
a quiz to test your understanding.
• Click the following image now (and at
anytime) to go to the main menu.
Main Menu
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What is Photosynthesis
Photosynthetic Pigments
Site of Photosynthesis
Photosystems – (Capture)
Light-Dependent Reactions – (Convert)
Light-Independent Reactions – (Store)
AP Biology Lab 4
Quiz
Photosynthesis
• Autotrophic organisms are able to manufacture
their own organic food molecules from inorganic
molecules. Most autotrophs use sunlight as
their energy source but some use inorganic
chemical bond energy in a process call
chemosynthesis.
• Autotrophs which contain the green pigment
chlorophyll (located in their chloroplast) are
able to convert solar energy into stored chemical
bond energy in a process called
photosynthesis.
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Photosynthesis
• The following reaction (in the presence of light)
summarizes the chemical process of
photosynthesis.
– Carbon dioxide + water  glucose + oxygen + water
– 6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
• This process can be broken down into 3 stages
– The capture of light energy
– The conversion of light energy into chemical energy
– The storage of chemical energy in sugar (carbon fixation)
• The first 2 stages are referred to as the light-dependent
reactions while the last stage refers to the light–
independent reactions.
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Overview
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Photosynthetic Pigments
• The sun radiates light energy in individual
packets called photons. The energy of a
photon corresponds to its wavelength.
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» Wavelength of Visible Light
• The first step in photosynthesis is the
capture of photons by pigments in the
chloroplast.
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Photosynthetic Pigments
• A pigment absorbs all colors that it does not
reflect.
• The chloroplast contains several types of
pigment molecules that absorb different
wavelengths of light.
• Chlorophyll is the key light capturing pigment
(containing > 120 atoms) found in the thylakoid
membrane of the chloroplast. It strongly
absorbs violet, blue, and red light but reflects
green, and therefore appears green. See graph
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Figure 1. Different types of pigments selectively absorb certain colors; the height of
each line represents the ability of each pigment to absorb light of each color.
Photosynthesis is driven to some extent by all of the colors of light,
owing to the absorption of light by several thylakoid pigments.
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Photosynthetic Pigments
• Thylakoids also contain other molecules
called antenna/accessory pigments, that
capture light energy and transfer it to
chlorophyll, thus expanding the spectrum
of light that can be used in photosynthesis.
• Carotenoids and xanthophylls  absorb blue and
green light and appear yellow, orange or red.
• Phycocyanins  absorb green and yellow light
and appear blue or purple.
– See graph
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Where Photosynthesis Happens
• The main photosynthetic structure of a plant
is the leave.
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- Mesophyll cells contain
the chloroplasts used in
photosynthesis.
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- Necessary CO2 and O2
exchange occurs via
Cross section of a leaf the stoma.
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Chloroplast
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Here we see a single mesophyll cell
and some of its major features
including a nucleus, vacuole,
and the green chloroplast
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Structure of a Chloroplast
Refer to diagram on preceding page
• The chloroplast is surrounded by a double
membrane enclosing a semifluid medium
know as stroma.
• Embedded in the stroma are disk-shaped,
interconnected membranous sacs called
thylakoids.
• A stack of thylakoids is referred to as
granum (grana, plural).
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Photosystems
• In the thylakoid membrane, chlorophyll,
antenna pigments, and electron-carrier
molecules form highly organized assemblies
called photosystems which capture light.
• Each thylakoid contains thousands of copies
of two different kinds of photosystems.
• Each is made up of 2 parts, a light harvesting
complex and an electron transport system.
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Photosystems
• These light-harvesting complexes consist of
a reaction center containing chlorophyll plus
antenna pigments.
• The reaction center is located next to the
electron transport system – a series of
electron carriers in the thylakoid membrane.
• The 2 photosystems are referred to as PS 1
and PS II or P700 and P680, respectively .
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Photosystems
• PS I (P700) absorbs light, on the average
in the 700 nm range.
• PS II(P680) absorbs light, on the average
in the 680 nm range.
• PS II activates before PS I
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Photosystem II
• Lets take a closer look
• In the following video you will see:
– The processes that take place in the PS II complex
– How chlorophyll pigments become excited by
light energy
– How an electron is transferred to the electron
transport chain
– How oxygen is generated form water
• VIDEO 
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Light-Dependent Reaction
• Occurs in clusters of molecules called
photosystems (in the thylakoid membrane)
• Energy from the sun is converted into
chemical energy in the form of adenosine
triphosphate (ATP) and nicotinamide
adenine dinucleotide phosphate (NADPH).
• This energy is needed to later fuel the light
independent (Calvin Cycle) in the stroma.
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Light-Dependent Reaction
• The reaction begins when light is
absorbed by chlorophyll pigments in PS II
located within the thylakoid membrane.
• An excited electron will then pass through
the electron transport chain until it reaches
PS I
• Through this process energy (ATP and
NADPH) is made.
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Light-Dependent Reaction
• Use the following animation to study the steeps
of the light-dependent reaction.
• Animation – click the play button (►) at the
bottom right to begin. Place your mouse over
each object to reveal the name of that object.
• When you have finished close the webpage and
return to this presentation. Click ‘next’ to see the
steeps in the light-dependent reaction.
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Light-Dependent Reaction
Process  **See diagram**
Light is harvested in photosystem II
This energy ejects electrons out of the reaction center
Electrons pass to the adjacent electron transport system
The transport system passes the electrons along, some of their
energy is used to pump hydrogen ions into the thylakoid interior.
A hydrogen gradient results and drives ATP synthesis
Light strikes photosystem I
PS I emits electrons
These electrons are captures by PS I electron transport system.
Electrons lost from PS I reaction center are replaced by those
coming from the transport system of PS II.
High energy electrons from PS I are captured by NADP+, which
becomes NADPH
The electrons lost from the reaction center of PS II are replaced
by electrons obtained from the splitting of water (photolysis).
This liberates oxygen (O2)
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⑨
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Lets go to the video!
• To see a video of the light reaction in
progress click the following link
– VIDEO 
• As the page loads, study the diagram
again
– **See diagram**
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Light-Dependent Reaction
Summary
• ATP is produced: The flow of electrons through
electron transport chains is coupled with the
phosphorylation of ADP to ATP via chemiosmosis
– ATP is needed to fuel the light independent reactions
(Calvin Cycle)
• Oxygen is produced: Water is split apart via
Photolysis to provide electrons for photosystem II
and protons to reduce NADP in photosystem I.
• NADPH is produced: NADP+ carries H2 to the
light-independent reactions (Calvin Cycle).
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Photophosphorylation
• The main process occurring during the lightdependent reaction.
• Light energy (‘photo’) is used to
‘phosphorylate’ ADP, forming ATP.
• Process begins at PS II and continues in PS I
• Electrons supplied by photolysis enter two
electron transport chains and ATP and NADPH
are formed
• Chemiosmosis powers the production of ATP
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Light-Independent Reactions
• Storing chemical energy in sugar
molecules, occurs in the stoma.
• ATP and NADPH (synthesized during the
light-dependent reactions) are dissolve in
the stoma, providing the energy to power
the synthesis of glucose from CO2 and H20.
• Reaction occurs independently of light as
long as ATP and NADPH are available.
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Light-Independent Reactions
• CO2 capture occurs in a set of reactions know as
the Calvin cycle or C3 cycle.
• The Calvin/C3 cycle requires;
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CO2 (normally from the air)
A CO2 capturing sugar, ribulose bisphosphate (RuBP)
Enzymes to catalyze all the reactions
Energy in the form of ATP and NADPH (from the lightdependent reactions)
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Calvin Cycle
• Use the following animation to study the steeps
of the Calvin Cycle.
• Animation – click the 5 carbon molecule RuBP to
begin. Use the flow chart on the right to proceed
steep by steep through the cycle.
• When you have finished close the webpage and
return to this presentation. Click ‘next’ to see the
parts of the Calvin cycle.
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Calvin Cycle
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CO2 (from the atmosphere) is chemically
reduced by hydrogen ions (produced in the
light-dependent reactions) to produce
carbohydrates
CO2 + H  CH2O (unbalanced)
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The Calvin/C3 cycle is best understood in three
parts (be sure to look at each before continuing)
1. Carbon fixation
2. Synthesis of phosphoglyceraldehyde (PGAL)
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A 3 carbon sugar
3. The regeneration of ribulose biphosphate (RuBP)
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Carbon Fixation
Section #1 of diagram
• The Calvin cycle begins and ends with a 5carbon sugar, RuBP.
• RuBP combines with CO2 from the
atmosphere to form an extreamly unstabe
6-carbon compound.
• This spontaneously reacts with H2O to form
two 3-carbon molecules of phosphoglyceric
acid PGA (hence C3 cycle)
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Synthesis of PGAL
Section #2 of diagram
• A series of enzyme-catalyzed reactions
occur.
• Energy donated by ATP and NADPH,
generated in the light reactions, is used to
convert PGA to phosphoglyceraldehyde
(PGAL).
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Regeneration of RuBP
Section #3 of diagram
• A complex series of reactions requiring
ATP energy occurs.
• Ten molecules of PGAL (10 x 3-carbon)
can regenerate 6 molecules of RuBP (6 x
5-carbon).
• These six RuBP molecules are used to
start the cycle again.
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Click to go back to Step
#1
Click to go back to Step
#3
Click to go back to Step
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Calvin Cycle
End Results
• The Calvin Cycle starts with 6 molecules of RuBP, adds CO2
to each, and ends with 6 molecules of RuBP again.
• The fixed carbon (from atmospheric CO2) has been
transformed and two molecules of phosphoglyceraldehyde
(PGAL) are left over.
• These two PGAL molecules (3-carbon each) combine to form
one glucose (6-carbon)
• Glucose can later be broken down (respiration) or linked
together to form starch (storage) or cellulose (cell walls), or
modified into other cellular contents.
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Lab Activity
• Go to the following link to review Plant
Pigments and Photosynthesis.
• Be sure to look at part II of the lab as
we do not have the materials at the
school to do this part of the lab.
• Click me 
Quiz
• The following is a short quiz covering
some of the important ideas of
photosynthesis.
• If you select a wrong answer, you will be
given an explanation of why it is incorrect.
• You can not move to the next question
until you choose the correct answer
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QUESTION #1
• Which of the following are products of
photosynthesis?
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A) Carbon dioxide and water
B) Carbon dioxide and glucose
C) Glucose and oxygen
D) Oxygen and caclcium
Q #1  A Incorrect
• A is incorrect because carbon dioxide and
water are the products of aerobic
respiration
Return to Question #1
Q #1  B Incorrect
• B is incorrect because only one of these is
a product of photosynthesis!
Return to Question #1
Q #1  C CORRECT 
• C is correct because the products of
photosynthesis are oxygen and glucose.
– Carbon dioxide + water  glucose + oxygen + water
• 6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
NEXT QUESTION
Q #1  D Incorrect
• D is incorrect because only one of these is
a product of photosynthesis!
Return to Question #1
QUESTION #2
• What is the name of the pigment used to
trap light energy during the process of
photosynthesis?
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A) PGAL
B) ATP
C) Chlorophyll
D) Stoma
Q #2  A Incorrect
• A is not correct because PAGL is the first
organic compound produced during
photosynthesis
Return to Question #2
Q #2  B Incorrect
• B is not correct because ATP is a chemical
found in living organisms used to store
and release energy.
Return to Question #2
Q #2  C CORRECT 
• C is the correct answer because the
chemical used to trap light energy during
photosynthesis is chlorophyll.
NEXT QUESTION
Q #2  D Incorrect
• D is incorrect because the stoma is the
region inside the chloroplast of the cell.
Return to Question #2
QUESTION #3
• A water molecule is split into hydrogen and
hydroxide ions during the process of
what?
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A) Chemosynthesis
B) Hydrolysis
C) Photolysis
D) Carbon fixation
Q #3  A Incorrect
• A is not correct because chemosynthesis
is the manufacturing of organic molecules
by using chemical energy located in
inorganic molecules.
Return to Question #3
Q #3  B Incorrect
• B is not correct because hydrolysis is the
splitting of two molecules with the addition
of water.
Return to Question #3
Q #3  C CORRECT 
• C is correct because photolysis is the
splitting of water molecules.
NEXT QUESTION
Q #3  D Incorrect
• D is not correct because carbon fixation is
the chemical process where atmospheric
carbon dioxide is captured by plants.
Return to Question #3
QUESTION #4
• What energy conversion occurs during the
process of photosynthesis?
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A) Light energy to nuclear energy
B) Chemical bond energy to light energy
C) Light energy to chemical bond energy
D) Mechanical energy to radiant energy
Q #4  A Incorrect
• A is not correct because this type of
energy conservation does not occur in
photosynthesis.
Return to Question #4
Q #4  B Incorrect
• B is not correct because this type of
energy conservation does not occur in
photosynthesis.
Return to Question #4
Q #4  C Correct 
• C is the correct answer because the
energy conservation that occurs during
photosynthesis is light energy to chemical
bond energy.
NEXT QUESTION
Q #4  D Incorrect
• B is not correct because this type of
energy conservation does not occur in
photosynthesis.
Return to Question #4
QUESTION #5
• The coenzyme that carries hydrogen
atoms from the light reaction to the dark
reaction is?
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A) NADP
B) Chlorophyll
C) ATP
D) RNA
Q #5  A CORRECT 
• A is the correct answer because NADP is
the coenzyme that carries hydrogen atoms
from the light reaction to the dark reaction.
End of Presentation
Q #5  B Incorrect
• B is not the correct answer because
chlorophyll is the chemical in
photosynthetic plants used to trap light
energy for food production.
Return to Question #5
Q #5  C Incorrect
• C is not the correct answer because ATP
is a chemical found in living organisms
used to store and release energy.
Return to Question #5
Q #5  D Incorrect
• D is not the correct answer because RNA
is a nucleic acid that aids in protein
synthesis.
Return to Question #5
THE END
Mr. Young
AP Biology 2007/2008