Cellular Respiration!
CA State Standard
CELL BIOLOGY
 1.g. Students know the role of the mitochondria in
making stored chemical-bond energy available to cells
by completing the breakdown of glucose to carbon
dioxide.
How do heterotrophs get energy?
They eat it!
When you eat food, how does it become the
energy that makes your body function?
Through a process called cellular respiration!
As this figure skater
breathes, she takes in
oxygen. Why?
The oxygen is used in
the process of cellular
respiration, which
allows her cells to break
down glucose and turn it
into ATP. This enables
her to have the energy to
perform her feats on ice.
What is Cellular Respiration?
Cellular Respiration is the
process that releases energy
by breaking down glucose
and other food molecules in
the presence of oxygen.
What is the equation for
Cellular Respiration?
Hint: It’s the opposite of Photosynthesis!
What is the equation for Cellular
Respiration?
Oxygen
What we breathe
6O2 + C6H12O6 6H2O + 6CO2 + Energy
Carbon Dioxide
Glucose
Water
What we exhale
Cellular Respiration has 3 Stages
1. Glycolysis
(occurs in the cytoplasm)
2. Krebs Cycle
(occurs in the mitochondria)
3. Electron Transport Chain
(occurs in the inner membrane of
the mitochondria)
Overview of Cellular Respiration
Glycolysis: Breakdown
of Glucose
Pyruvic acid
Cytoplasm
Krebs Cycle and Electron Transport
Chain: Production of ATP
Pyruvic
Acid
Alcohol &
CO2 or
Lactic Acid
ATP!
Glycolysis
 Glyco = sugar; lysis = breaking; so glycolysis is the breaking
of glucose!
 It occurs in the cytoplasm of the cell.
 Glycolysis – the process in which one
molecule of glucose is broken in half,
producing two molecules of pyruvic
acid, a 3-carbon compound. 2 ATP
molecules and 2 NADH molecules are
created.
During Glycolysis, glucose is
converted to pyruvic acid, producing a
small amount of ATP and NADH.
Cellular respiration occurs
in three stages.
Pyruvic Acid
Glycolysis Step 1
1. Phosphate groups from 2 ATP are transferred to a
glucose molecule
Glycolysis Step 2:
2. Six-carbon compound broken down to two 3-carbon
compounds, each with a phosphate group.
Glycolysis Step 3:
3. Two NADH molecules are produced, one phosphate group
is transferred to each 3-carbon compound.
Glycolysis
Step 4:
4. Two 3- carbon compounds converted to pyruvic acid and 4
molecules of ATP
Glycolysis
Glycolysis has a net
gain of 2 ATP.
(It uses 2 ATP but
produces 4 ATP)
What happens in the stages
of glycolysis?
1. A molecule of
glucose is split
2. 2 pyruvic acids are
made
3. 2 ATP and 2
NADH are
produced
An important example of
an electron acceptor
that functions in
glycolysis is…
NAD+
NAD+ becomes
NADH when it
accepts an e-
What happens after Glycolysis….?
 Only 2 ATP were
made and pyruvic
acid still has a lot of
energy in its
bonds…
 If there is O2 available

AEROBIC
RESPIRATION!
 If there is NO O2
available 
FERMENTATION
(ANAEROBIC)
Aerobic Respiration
Pyruvic
Acid
Aerobic =
requires O2
When oxygen is present, pyruvic acid and NADH are
used to make a large amount of ATP in the
Mitochondrion during the Krebs Cycle and Electron
Transport Chain.
Fermentation (Anaerobic respiration)
Pyruvic Acid
When oxygen is not present, pyruvic acid is
converted to either lactic acid or alcohol and
carbon dioxide through fermentation.
Two Types of Fermentation:
Alcoholic Fermentation
Lactic Acid Fermentation
Two Types of Fermentation:
Alcoholic Fermentation
 Pyruvic acid + NADH  alcohol +
CO2 + NAD+
 WHO? Yeast and other
microorganisms
 Example: This is how bread and
alcohol are made!
Two Types of Fermentation:
Lactic Acid Fermentation
 Pyruvic acid + NADH  lactic acid +
NAD+
 WHO? Animals, prokaryotes
 Examples:
 Lactic acid build-up creates sore muscles after
intense exercise
 Cheese, yogurt, sour cream, pickles, kimchi
are made this way
Fermentation makes cheese!
Fungi or bacteria are
added to milk to carry
out lactic acid
fermentation on some of
the sugar in the milk.
This is how cheese is
made!
Lactic Acid
Fermentation!
If OXYGEN is available….
CELLULAR RESPIRATION
TAKES PLACE!
When oxygen is available,
Pyruvic Acid goes into the mitochondrion and
goes through the Krebs Cycle and Electron
Transport Chain to get ATP!
 Krebs Cycle
occurs in area
enclosed by inner
membrane.
 Electron
Transport Chain
occurs within
inner membrane
itself.
Cellular Respiration
1. Glycolysis
(breakdown of glucose)
2. Krebs
Cycle
3. Electron
Transport
Chain
Production of ATP!
2. KREBS CYCLE
 Pyruvic acid from
glycolysis enters the
mitochondria and gets
transformed into AcetylCoA and other carbon
compounds.
 CO2 is produced.
 8 ATP, FADH2 and
NADH are created.
 Occurs in the
mitochondria
KREBS CYCLE
1. When oxygen is
present, pyruvic acid
enters the
mitochondrion and is
converted to a
compound called
Acetyl-CoA.
2. CO2 is released.
Pyruvic
Acid
Citric Acid
Krebs
Cycle
Acetyl-CoA
3. Acetyl-CoA is converted into Citric Acid, releasing
more CO2.
Citric Acid
4. More CO2 is released from the 6-carbon
compound, forming a 5-carbon compound.
5. Electrons are transferred to NAD+ making NADH.
6. More CO2 is released when Citric Acid is converted
into a 5-carbon compound.
7. ATP and NADH are made.
8. Electrons are transferred to FAD making
FADH2
9. The 4-carbon compound is converted back
into citric acid and the cycle starts all over!
NADH and FADH2 go into the Electron Transport
Chain, providing high-energy electrons, leading
to the production of ATP!
Electron
Transport
Chain
The Electron
Transport
Chain occurs
in the inner
membrane of
the
mitochondria.
Inner membrane of
mitochondria
1. High-energy
electrons from
NADH and
FADH2 are
passed along
proteins in the
membrane.
Inner membrane of
mitochondria
2. At the end of the
electron transport
chain, OXYGEN is the
final electron
acceptor of the
electrons. The
electrons combine with
hydrogen ions and
form WATER!
The final electron acceptor in
aerobic respiration is
Oxygen!
The final end product in the
electron transport chain is
water
3. As the highenergy electrons
are passed along,
their energy is
used to pump
hydrogen ions,
H+, across the
membrane. This
creates a
concentration
gradient.
Inner membrane of
mitochondria
4. ATP is
created as
H+ ions
diffuse
through ATP
Synthase, a
channel
protein in the
membrane.
ATP
Synthase
The complete
breakdown of
glucose
through
glycolysis and
respiration
results in the
production of
chemical
energy in the
form of 36
total
molecules
of ATP.
Cellular Respiration Quiz
1. What is cellular respiration?
2. What is the balanced equation for cellular respiration?
3. Glycolysis occurs in the mitochondrion/cytoplasm of the cell. (circle the
correct response)
4. Glucose is broken down in glycolysis/Krebs Cycle/ electron transport
chain. (circle the correct response)
5. CO2 is produced in glycolysis/Krebs Cycle/ electron transport chain.
(circle the correct response)
6. The Krebs Cycle occurs in the mitochondrion/cytoplasm of the cell.
(circle the correct response)
7. Why do we need to breathe oxygen?
8. After glycolysis, if there is no oxygen present, what process occurs instead
of the Krebs Cycle and electron transport chain?
Cellular Respiration Review!
Standardized Test Prep When oxygen is
present, most of the ATP made in cellular
respiration is produced by
A aerobic respiration.
B glycolysis.
C alcoholic fermentation.
D lactic acid fermentation.
What is the equation for
cellular respiration?
What is the equation for Cellular
Respiration?
Oxygen
What we breathe
6O2 + C6H12O6 6H2O + 6CO2 + 36 ATP (Energy)
Carbon Dioxide
Glucose
Water
What we exhale
What are the three stages of
Cellular Respiration?
Cellular Respiration has 3 Stages
1. Glycolysis
(occurs in the cytoplasm)
2. Krebs Cycle
(occurs in the mitochondria)
3. Electron Transport Chain
(occurs in the inner membrane of
the mitochondria)
What does glycolysis do?
 Breaks down glucose into 2
pyruvic acid molecules, 2 ATP
molecules and 2 NADH
molecules.
Where does glycolysis take
place?
The cytoplasm
What happens if there is no
O2 available?
 Fermentation Alcohol or
 Lactic Acid
What happens if O2 is
available?
Krebs Cycle and
Electron Transport Chain
What goes into the Krebs
Cycle?
Pyruvic Acid!
What comes out of the Krebs
Cycle?
CO2 that we breathe out
NADH and FADH2
ATP
Where does the Electron
Transport Chain occur?
In the inner membrane of
the mitochondria!
What goes into the Electron
Transport Chain?
ELECTRONS!
DUH!
Seriously though, the
electrons come from NADH
and FADH2
What is the main purpose of the
Electron Transport Chain?
To make ATP!
What molecule is the final
electron acceptor for electrons
in the Electron Transport
Chain?
HINT: YOU BREATHE IT IN.
OXYGEN GAS! (02)
What molecule results when O2
accepts electrons at the end of the
Electron Transport Chain?
WATER! (H20)
How many net ATP molecules
are created from cellular
respiration?
36 ATP Molecules!
Review
List the products of glycolysis. What is the role
of each of these products in cellular respiration?
Summarize the roles of the Krebs cycle and the
electron transport chain during aerobic
respiration.
Describe the role of fermentation in the second
stage of cellular respiration.
Critical Thinking Comparing Functions
Explain why cellular respiration is more
efficient when oxygen is present in cells.
Critical Thinking Inferring
Conclusions Excess glucose in your
blood is stored in your liver as
glycogen. How might your body sense
when to convert glucose to glycogen
and glycogen back to glucose?
Leftover slides…
Respiration, an aerobic process, takes place in
the mitochondrion. The Krebs cycle takes place
in the area enclosed by the inner mitochondrial
membrane. Electron transport and ATP formation
involve complex molecules embedded in the
inner membrane.
Acetic acid
6- carbon compound
The Krebs Cycle
 Continuing series of reactions
 Pyruvic acid travels from cytoplasm to mitochondrion
Acetic Acid
• 1st step respiration: pyruvic acid broken
down into carbon dioxide and acetic acid.
Krebs cycle
Acetic acid
6-carbon compound
 Acetic acid enters Krebs cycle reacts with 4-carbon
compound to produce citric acid.
Inner
mitochondria
membrane
The high-energy electrons in the energy-storing compounds
NADH and FADH2 are transferred to the molecules of the
electron transport chain, which is located is the inner
mitochondria membrane.
At the end of the chain,
the electrons react
with hydrogen ions
and oxygen to form
water.
Krebs cycle
 2 carbon atoms added – from breakdown of pyruvic
acid
 2 carbon atoms removed (in 2 molecules of CO2)
Krebs cycle
 3 molecules of NAD+ converted to NADH
 1 molecule of FAD converted to FADH2
 1 molecule of GDP converted to GTP
Acetic acid
6- carbon compound
Electron Transport in the
Mitochondrion
 High-energy electrons from NADH and FADH2 are passed
to a series of electron transport enzymes in the inner
membrane of mitochondrion
 At end of chain an enzyme combines electrons , hydrogen
ions and O2 to form water.
 Oxygen is the final electron acceptor.
 Oxygen essential for obtaining energy from NADH and
FADH2
ATP Formation
 Movement of hydrogen ions powers formation of ATP.
 The movement of a pair of electrons down ETC
produces 3 ATP from ADP
 More hydrogen ions outside the inner membrane
 Hydrogen ions pumped across membrane
Breathing and Respiration
 Oxygen is final acceptor for all electrons produced in
respiration.
 Without oxygen ETC cannot operate, Krebs cycle stops
and synthesis of ATP stops.
 Breathing gives us a constant supply of oxygen.
Obtaining Energy from Food
 Complex carbohydrates broken down into simple
sugars that are converted into glucose.
 Lipids & proteins can be broken down into molecules
that can enter glycolysis at one of several places
 The cell can generate ATP from many sources.
4-5 ATP Synthesis
 The difference in electrical charges across the
photosynthetic and mitochondrial membranes a
source of energy. This energy could be used to
attach a phosphate to ADP to make ATP.
 ATP is generated when hydrogen ions move from a
high concentration to a low concentration. This is
called chemiosmosis.
1. Define glycolysis.
2. Compare lactic acid fermentation and
alcoholic fermentation.
3. Critical Thinking-Inferring What would
happen to wine if there was an air leak in
the fermentation tank?
4. MIN) LAB Predict the effect that
temperature has on the rate of
fermentation.
Energy in Balance
 Photosynthesis and respiration can be thought of as
opposite processes.
 Photosynthesis is the storing of energy.
 Cellular respiration is using energy.
 The products of photosynthesis ar eht reactants of
glucose breakdown
 The products of glucose breakdown are the reactans of
photosynthesis.
 Photosynthesis is to oxygen as
cellular respiration is to what?
• Carbon dioxide
Cellular Respiration
1. Summarize how glucose is broken down in the first
stage of cellular respiration.
2. Describe how ATP is made in the second stage of
cellular respiration.
3. Identify the role of fermentation in the second stage
of cellular respiration.
4. Evaluate the importance of oxygen in aerobic
respiration.