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Chapter 5
Photosynthesis and
Cellular Respiration
Energy & Living Things
Directly or Indirectly almost all of the
energy comes from the SUN
 Metabolism
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Using energy to build molecules
Breaking down molecules where energy is
stored
Building Molecules That Store
Energy
Photosynthesis – is the process by
which light energy is converted to
chemical energy
 Autotrophs – organisms that use the
sun to convert inorganic substances
into organic substances
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Breaking Down Food For
Energy
Heterotrophs – must eat food to get
energy
 Cellular Respiration – process by which
cells produce energy from
carbohydrates
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O2 + C6H12O6  H2O + CO2
Releases energy to make ATP
Transfer of Energy to ATP
Energy is released in a series of enzyme
assisted chemical reactions
 Food Breaks down into
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1) Heat Energy
2) Portable Energy (ATP)
ATP drives most cellular activity
Adenosine Triphosphate
3 Phosphate Groups
 5 Carbon Sugar (Ribose)
 Phosphate Tail is negatively charged
 Energy is released when phosphate
bonds are broken
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H2O + ATP  ADP + P + energy
Energy released powers metabolism
Section 1 Review
1. What is the primary source of
energy that flows through most living
systems?
 2. Organisms that can make their own
food using energy from the sun are
called ___________.
 3. How is energy released from ATP?
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Photosynthesis
Stage 1: Energy is captured from
sunlight
 Stage 2: Light energy is converted to
chemical energy, which is temporarily
stored in ATP and the energy carrier
molecule NADPH
 Stage 3: ATP & NADPH powers the
formation of organic compounds using
CO2
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Photosynthesis
6CO2 + 6H2O  C6H12O6 + 6O2
 Important for life processes
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Sugars form starch
Starch is broken down to produce ATP
Sugar fragments form Proteins, Nucleic
Acids & other molecules
Stage 1: Absorption of Light
Energy
“Light Dependent Stage”
 Require Sun Light
 Pigments – light absorbing substances
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Carotenoids & Chlorophyll –a and b
 Pigments in plants
 Enables plants to absorb more light
 Located in the Thylakoids of a
chloroplast
Production of Oxygen
Electrons get “excited”
 Electrons leave the chlorophyll
 Replaced by e- from split H2O molecules
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H electron replaces excited electron
Leaving H+ ions & O2 (oxygen gas)
Electrons are used to power the 2nd stage
of Photosynthesis
Stage 2: Conversion of Light
Energy
Excited e- are used to make ATP
 Electron Transport Chains
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1st Located b/t 2 chlorophyll pigments
 Contains a protein that acts as a membrane
pump
 Excited e- pass through the protein
 Electrons lose energy
 Energy is used to pump H+ into the
thylakoid
1st Electron Transport Chain
H+ ions are also produced when H2O
molecules split
 H+ are highly concentrated inside
 H+ diffuse out of the thylakoid – down
the concentration gradient through
carrier proteins
 Carrier Proteins – act as an Ion Channel
& Enzyme
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1st Electron Transport Chain
1.
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 3.
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 5.
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H+ pass through the channel
The protein catalyzes a reaction
A Phosphate group is added to ADP
ATP is made
ATP is used to power Stage 3
2nd Electron Transport Chain
Provides energy to make NADPH
 NADPH – is an electron carrier that
provides the high energy e- needed to
make C-H bonds in stage 3
 NADP – is and electron acceptor
 E- + H ions + NADP+  NADPH
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Light Dependent Stages
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Summary (Stages 1 & 2)
 1) Pigment molecules in the thylakoid absorb
light
 2) E- are excited by light & move through 2
Electron Transport Chains
 3) Excited e- leaving the thylakoid are replaced
by e- from H20 that is split by an enzyme
 4) O atoms combine and form O2
 5) H+ accumulate inside the thylakoid setting up
a concentration gradient that provides the
energy to make ATP
Stage 3: Storage of Energy
Light Independent Stage
 Carbon atoms are used to make organic
compounds to store chemical energy
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CARBON DIOXIDE FIXATION
The Calvin Cycle
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A series of enzyme-assisted chemical
reactions that produce a 3-C sugar
Calvin Cycle
Melvin Calvin
 Step 1: Enzymes add CO2 to a 5-C
compound
 Step 2: The 6-C compound splits into
two 3-C compounds
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P groups form ATP
Electrons form NADPH
Both are added forming 3-C sugars
Calvin Cycle
Step 3: One 3-C sugar is used to make
organic compounds
 Step 4: Other 3-C sugars are used to
regenerate the initial 5-C compound
 The organic compounds provide the
organism with energy for growth &
metabolism
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Factors that Affect
Photosynthesis
#1 – Light
 #2 – Carbon Dioxide
 #3 – Temperature
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Section 2 Review
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1. T/F Chloroplasts are found within the
thylakoid membrane.
2. T/F Carbon Dioxide fixation takes place
during the Calvin Cycle.
3. The electron transport chain converts light
energy to chemical energy during the __
stage of photosynthesis.
4. During photosynthesis, plants store
energy in this…
Section 3: Cellular Respiration
Energy is stored in proteins,
carbohydrates and fats
 Cells transfer the energy in organic
compound to ATP through CELLULAR
RESPIRATION
 Metabolism  describes the sum of all
chemical reactions
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Aerobic = Requires Oxygen
Anaerobic = Does NOT require Oxygen
Cellular Respiration
C6H12O6 + 6O2  6CO2 + 6H2O + ENERGY
 Takes place in the Mitochondria
 Stage 1: Glucose is converted to Pyruvate,
producing small amounts of ATP and NADH
 Stage 2:
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Aerobic Respiration – Pyruvate & NADH make
large amounts of ATP
Anaerobic Respiration – Pyruvate is converted into
Lactic Acid or Ethanol & CO2
Stage 1: Breakdown of
Glucose
Fuel – Glucose
 Glucose is broken down in the
cytoplasm during GLYCOLYSIS
 Glycolysis – is an enzyme assisted
anaerobic process that breaks down
one 6-C molecules into two 3-C
pyruvate ions
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Stage 1: Breakdown of
Glucose
Pyruvate – is the ion of a 3-C organic
acid called pyruvic acid
 Broken down glucose transfers H+ ions
to NAD+ forming NADH
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NAD + is an electron acceptor
NADH is an electron carrier
NADH donates electrons to organic
compounds turning back into NAD
Summary of Stage 1
1. Phosphate groups from 2 ATP molecules
are transferred to glucose (3 reactions)
 2. 6-C compound is broken into two 3-C
compounds, each with a Phosphate group (2
reactions)
 3. 2 NADH molecules are produced, 1
phosphate group is transferred to a 3-C
compound
 4. Each 3-C compound is converted into a 3-C
pyruvate, producing 4 ATP molecules
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Stage 1 to Stage 2
Glycolyisis uses 2 ATP molecules to
make 4 ATP molecules – 2 net ATPs
 Pyruvate produced in glycolysis enters
the mitochondria and is converted into
a 2-C compound
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1 – CO2
1 – NADH
1 – acetyl-CoA
Stage 2: Production of ATP
Acetyl-CoA enters a series of enzyme
assisted reactions called the KREBS CYCLE
 Step 1: Acetyl-CoA combines with a 4-C
compound forming a 6-C compound &
releasing Coenzyme A
 Step 2: CO2 is released from the 6-C
compound forming a 5-C compound
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Electrons + NAD  NADH
Stage 2: Production of ATP
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Step 3: CO2 is released from the 5-C
compound resulting in a 4-C compound
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Step 4: 4-C compound is converted to a new
4-C compound
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ATP & NADH is made
Electrons are transferred from FAD to FADH2
Step 5: The new 4-C compound is converted
to the 4-C compound that began the cycle
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Another NADH molecule is produced
After the Krebs Cycle
NADH & FADH2 contain much of the energy
previously stored in glucose & pyruvate
 Donated electrons from NADH & FADH2
enter the Electron Transport Chain in the
mitochondria membrane
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Electrons are used to help move H+ ions
ATP & O2 is produced
Anaerobic Respiration
Electron Chain does NOT function
 NAD+ has to be recycled in another way
 Recycling NAD+ using an organic H acceptor
is called FERMENTATION
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1. Lactic Acid – exhausted muscles, yogurt &
cheese
2. Alcoholic Fermentation – releases CO2 –
making bread, beer & wine
Production of ATP
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After Glycolysis 1 of 2 paths:
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1. Oxygen Present  Krebs Cycle
2. Oxygen Absent  Fermentation
ATP Produced
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Fermentation – None
Krebs Cycle – 2
Electron Transport Chain  34 ATP