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Cellular Respiration
How We Obtain Chemical Energy
from Food.
Learner Outcomes:
 1. I can explain the relationship between
cellular respiration and photosynthesis.
 2. I can write the overall equation for
cellular respiration and identify the
products and reactants.
 3. I can describe the three stages of
cellular respiration.
Energy Flow and Chemical
in the
Fuel molecules in food represent solar energy.
 Energy stored in food can be traced back to the sun.
 Animals depend on plants to convert solar
energy to chemical energy.
 This chemical energy is in the form of sugars and
other organic molecules.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Chemical Cycling between
Photosynthesis and Cellular
 The ingredients for photosynthesis are carbon
dioxide and water.
 CO2 is obtained from the air by a plant’s leaves.
 H2O is obtained from the damp soil by a plant’s roots.
 Chloroplasts rearrange the atoms of these
ingredients to produce sugars (glucose) and
other organic molecules.
 Oxygen gas is a by-product of photosynthesis.
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings
Chemical Cycling between
Photosynthesis and Cellular
 Both plants and animals
perform cellular
 Cellular respiration
harvests energy from
organic molecules.
 Occurs in mitochondria.
 The waste products of
cellular respiration, CO2
and H2O, are used in
Cellular Respiration
 ATP-producing process in which the
ultimate electron acceptor is Oxygen
 Is an exergonic process (releases
The Relationship between
Cellular Respiration and
 Cellular respiration
requires a cell to
exchange gases with
its surroundings.
 Breathing exchanges
these gases between
the blood and outside
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings
Cellular Respiration
 Carbohydrates, Proteins, and fats can all be
broken as fuel, but cellular respiration most
often described as:
C6H12O6 + 6O2  6CO2 + 6H2O + Energy (ATP + Heat)
 Process transfers energy stored in food
molecules to ATP
 The Process of Cellular
Respiration: Process that releases energy
by breaking down food in presence of oxygen.
three main metabolic stages:
1. Glycolysis
2. Krebs Cycle
3. Electron Transport
Chain and
Overview continued
 Takes place in the cytoplasm of the cell
and the mitochondria.
 Equation:
 6O2 + C6H12O6  6CO2 + 6H20 + energy
 How is this equation related to the
photosynthesis equation?
 The process in which
one molecule of
glucose is broken
down in half.
 Takes place in
 This produces two
molecules of pyruvic
acid, a 3-carbon
Glycolysis continued
 The cell has to contribute 2 ATP molecules at
the beginning of glycolysis to get things going.
 4 ATP molecules have been produced at the
end of glycolysis for a net gain of 2 ATP.
 Although the energy yield is small, the process
is so fast that cells can produce thousands of
ATP molecules in milliseconds.
 Does not require oxygen.
Aerobic respiration
 At the end of glycolysis, about 90 percent
of the chemical energy that was available
in glucose is still unused (pyruvic acid)
 Cell turns to oxygen for final steps of
cellular respiration.
 Krebs Cycle
 Electron Transport Chain
Krebs Cycle
 Named after Hans
 During this cycle,
pyruvic acid is
broken down into
carbon dioxide in a
series of energyextracting reactions.
 Takes place in
Electron Transport Chain
 The Krebs Cycle spins round and round
to produce high-energy electrons, which
are then passed to the electron transport
 The ETC uses these high-energy
electrons to convert ADP into ATP.
 Takes place in cristae: folds in
The Totals:
 How much energy does cellular
respiration yield from a single molecule of
 2 molecules of ATP from glycolysis
 34 molecules of ATP from Krebs Cycle and
Electron transport chain.
 Total ATP from one molecule of glucose: 36
Totals Continued
 18 times as much ATP can be generated
from glucose in the presence of oxygen
then without.
 How efficient is cellular respiration? 36
ATP represent about 38 % of the total
energy of glucose.
 What happened to other 62%?
Review of Cellular
 Process that releases
energy by breaking
down food in presence
of oxygen.
 Three processes make
up cellular respriation:
 Glycolysis
 Krebs Cycle
 Electron Transport Chain
Anaerobic respiration: No
 Fermentation:
releases energy from
food molecules in the
absence of oxygen.
 Two main types:
 Alcoholic
 Lactic acid
Alcoholic Fermentation
 Occurs in plant cells
and some
 Alcohol is produced
as a by-product of
ATP production.
 Important in bread,
cheese, wine
Lactic Acid Fermentation
 Occurs in animal
cells when oxygen
is not present.
 Lactic acid is
produced as a byproduct of
producing ATP
without oxygen.
Energy and Exercise
 To obtain energy
during exercise, the
body uses ATP
already in muscles
and new ATP made
by lactic acid
fermentation and
cellular respiration.
The Effect of Exercise on
Physical Activity
 As the activity level
increases, so does
the rate of cellular
respiration (and thus
your breathing rate).
 Your body must take
in more oxygen to
supply enough ATP
to cells for activity.
Quick energy: What happens
when your body needs energy
 Cells can provide
enough energy from
ATP for a few seconds.
 After this, ATP is
produced by lactic acid
fermentation; enough for
about 90 seconds.
 Lactic acid builds up in
you and this is why
muscles get sore!!
Long-Term Energy: Sustained
energy over a long period of
 For exercise over 90
seconds, cellular
respiration is the only
way to generate a
continuing supply of
 This is why our breathing
rate increases during
 Energy is stored in the
body as the
carbohydrate glycogen:
15-20 minutes. After
that, body begins to
break down other
molecules, such as fat.