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Photosynthesis
Energy & Lifecopyright cmassengale
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The Photosynthesis Equation
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Redox Reactions
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Redox Reaction
The transfer of one or more electrons from one reactant to another
Two types:1. Oxidation is the loss of e-
2. Reduction is the gain of e-
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Oxidation Reaction
The loss of electrons from a substance or the gain of oxygen.
Example: Burning“Breaking Down Compounds”
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Reduction Reaction
The gain of electrons to a substance or the loss of oxygen.
“Building Up Compounds”
Question: If electrons are gained, what happens to the CHARGE of the molecule?
Would photosynthesis be considered an
oxidation reaction or a reduction reaction?
Why?
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Photosynthesis
Photosynthesis is the REDUCTION of
Carbon Dioxide (CO2) into
Glucose (C6H12O6)
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6CO2 + 6H2O 6O2 + C6H12O6
Reduction
PHOTOSYNTHESISThe Reactions
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Photosynthesis• Anabolic (small molecules combined)
consume energy to build molecules from simpler ones
• Endergonic (stores energy)absorbs free energy from its surroundings
• Carbon dioxide (CO2) requiring process that uses light energy (photons) and water (H2O) to produce organic macromolecules (glucose).
6CO2 + 6H2O C6H12O6 + 6O2glucose
SUNphotons
Electron Carriers
Electron carriers are molecules that will “pick up” one or two
hydrogen ions and electrons and carry them to another location.
Examples: Photosynthesis = NADP +
Cellular Respiration = NAD + & FAD+
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Photosynthesis Overview
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1st Step of Photosynthesis• Light-Dependent Reactions
–Requires light (Energy Source)–Occurs in the Thylakoids
•In the Chlorophyll (inside the Thylakoids)
•Across the Membrane of the Thylakoids
Light-Dependent Reactions• These reactions use water molecules to
produce oxygen gas.• They use energy from light to produce
ATP and NADPH (an electron carrier).• They convert
–ADP into ATP–NADP+ into NADPH
Light-Dependent Big Idea
Light is absorbed by chlorophyll to split water
molecules and give off oxygen.
This “charges up” the energy molecules ATP and
NADPH.
2nd Step of Photosynthesis
• Calvin Cycle – a.k.a. Light-Independent Reactions or
Carbon Fixation
–Does NOT require light•Uses Energy Storage Molecules (ATP & NADPH)
–Occurs in the Stromacopyright cmassengale 16
Calvin Cycle (Light-Independent Reactions)
• Uses CO2 and the “Left-over” Hydrogen from NADPH.
• Produces Glucose (C6H12O6).
• These reactions use the ATP and NADPH produced in the light-dependent reactions to produce high-energy sugars.
Calvin Cycle Big Idea (Light-Independent)
Energy is used from ATP and NADPH.
The “left-over” hydrogens from the water are carried to the
stroma by NADPH.
They are combined with CO2 to make glucose.
Light Dependent Calvin Cycle• Energy Source= Light• Occurs in the Thylakoids
(Chlorophyll & membranes)
• Changes ADP into ATP• Changes NADP into
NADPH• Uses H2O
• Produces Oxygen Gas
• Energy Source = ATP and NADPH
• Occurs in the Stroma• Changes ATP into ADP• Changes NADPH into
NADP• Uses CO2 & “left-over” H
from NADPH• Produces Glucose
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Photosynthesis Overview
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Light Dependent Reaction
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Thylakoid membranes
• Light Dependent reactions occur here
• Photosystems are made up of clusters of chlorophyll molecules integrated into the thylakoid membrane
• The two photosystems are: Photosytem I &
Photosystem II copyright cmassengale
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• Occurs across the thylakoid membranes
• Uses light energy• Produce Oxygen from
water• Convert ADP to ATP• Also convert NADP+ into the energy carrier NADPH
Light Dependent Reactions
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Light Dependent Reaction
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Light Dependent Reaction
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Photosystem II
•Discovered Second but OCCURS FIRST•Contains about equal amounts of chlorophyll a and chlorophyll b•Photosystem II absorbs light energy•SPLITS H2O into O2
•Excites Electrons!copyright cmassengale
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Photosynthesis Begins
Electrons are energized and passed to the Electron Transport Chain
Lost electrons are replaced from the splitting of water into 2H+, free electrons, and Oxygen
2H+ pumped across thylakoid membrane (active transport)
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Noncyclic Electron Flow
P700
Photosystem IP680
Photosystem II
PrimaryElectronAcceptor
ETC
H2O
1/2O2 + 2H+
ATPPhoton
2e-
2e-
2e-SUN
H2O is split in PSII & ATP is made
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Photosystem I
•Discovered First but occurs SECOND•Almost completely chlorophyll a•MAKES NADPH
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Photosystem I• High-energy electrons are
moved to Photosystem I through the Electron Transport Chain
• Energy is used to transport H+ from stroma to inner thylakoid membrane
• NADP+ converted to NADPH when it picks up 2 electrons & H+
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Noncyclic Electron Flow
P700
Photosystem IP680
Photosystem II
PrimaryElectronAcceptor
PrimaryElectronAcceptor
ETC
EnzymeReaction
H2O
1/2O2 + 2H+
ATP
NADPH
Photon
2e-
2e-
2e-
2e-
2e-
SUN
Photon
The energy carrier NADPH is made in PSI
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Noncyclic Electron Flow
• ADP + ATP• NADP+ + H NADPH• Oxygen comes from the
splitting of H2O, not CO2
H2O 1/2 O2 + 2H+
P
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ChemiosmosisH+ H+
ATP Synthase
H+ H+ H+ H+
H+ H+high H+
concentration
H+ADP + P ATP
PS II PS IE
TC
low H+
concentration
H+ThylakoidSpace
Thylakoid
SUN (Proton Pumping)
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Chemiosmosis• Powers ATP synthesis• Takes place across the
thylakoid membrane• Uses ETC and ATP synthase
(enzyme)• H+ move down their
concentration gradient through channels of ATP synthase forming ATP from ADP
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Light Reaction Summary
Reactant: H2O
Also Needed: Light Energy, Chlorophyll, ADP & NADP
Products:• O2 (PS II; released into atmosphere)
• ATP (chemiosmosis)
• NADPH (PS I; used in the Calvin Cycle)
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Light Dependent Reaction Simulation
• http://www.youtube.com/watch?v=RFl25vSElaE
• Video http://www.youtube.com/watch?v=v590JJV96lc
• Rap http://www.youtube.com/watch?v=pE82qtKSSH4
• Light Dependent Claymation http://www.youtube.com/watch?v=CLf4yu8Iwo0
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The Calvin Cycle
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REMEMBER
• The following were produced during the Light-Dependent Reaction:–O2 (released into the atmosphere)
–NAPDH & ATP (used for ENERGY in the Calvin Cycle)
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2nd Step of Photosynthesis
Calvin Cycle • aka Light Independent
Reaction, Dark Reaction, Carbon Fixation or C3 Fixation
• Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).
• Occurs in the stroma • Uses 6 CO2
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Chloroplast
GranumThylakoid
STROMA– where Calvin Cycle occursOuter Membrane
Inner Membrane
Calvin Cycle• RuBP (a 5-carbon sugar)
attaches to each CO2 forming a temporary 6-carbon sugar
• This 6-carbon sugar splits apart into 2 3-carbon sugars called PGA
• PGA exchanges Hydrogen and Oxygen to transform into G3Ps (a different 3-carbon sugar)
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Calvin Cycle (continued)• 2 G3Ps combine to form Glucose (C6H12O6)
• The other G3Ps combine to become RuBP molecules
• To produce 1 Glucose molecule–6 turns of the cycle–Uses 18 ATP and 12 NADPH–“Fixes” 6 CO2 molecules into a usable form for organisms
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Calvin Cycle (C3 fixation)
6CO2
6C-C-C-C-C-C
6C-C-C 6C-C-C
6C-C-C-C-C
12PGA
RuBP
12G3P
(unstable)
6NADPH 6NADPH
6ATP 6ATP
6ATP
C-C-C-C-C-CGlucose
(6C)(36C)
(36C)
(36C)
(30C)
(30C)
(6C)
6C-C-C 6C-C-C
C3
glucose
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Calvin Cycle
Remember: C3 = Calvin
Cycle
C3
Glucose
• Big Idea: 6 CO2 molecules are “fixed” into Glucose (C6H12O6)
• ADP & NADP+ are reused in the next light-dependent reaction
More Videos• Calvin Cycle Claymation
https://www.youtube.com/watch?v=hhkpJwSDxQQ • Calvin Cycle Animation
https://www.youtube.com/watch?v=E_XQR800AgM• Crash Course Biology: Photosynthesis
https://www.youtube.com/watch?v=sQK3Yr4Sc_k
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How do these large trees get all their mass?
• Complete the Life Science Assessment Probe – Giant Sequoia Tree
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