Chapter 9
Cellular Respiration
•  The process of
breaking down food
molecules to release
energy
•  Plants, algae,
animals, and some
bacteria use cellular
respiration to break
down food
molecules
•  The energy released
through cellular
respiration is used to
create ATP
•  Cellular respiration
occurs in three
phases:
–  Glycolysis
–  Krebs cycle
–  Electron transport
•  The process starts
with a molecule of
glucose
•  The reactions of
cellular respiration
occur with the use of
enzymes
•  Respiration is the
primary means by
which cells obtain
useable energy
Glycolysis
•  First phase in
cellular respiration
•  This step occurs in
the cytoplasm of the
cell, and it can occur
whether or not
oxygen in present
Glycolysis
•  In this phase, the
glucose molecule (a
6-carbon sugar) is
broken in half
through a series of
reactions
Glycolysis
•  The energy released
by breaking down
the glucose converts
into ATP.
Glycolysis
•  Additionally, some high energy electrons are
removed from the sugar during glycolysis
•  These electrons pass on to an electron carrier called
NAD+, converting it to NADH.
•  These electrons will later be used to create more
energy
•  If oxygen is present,
the 3-carbon sugars
produced from
glycolysis enter the
mitochondria, along
with the oxygen
•  As the sugars enter
the mitochondria,
they convert to citric
acid in phase two of
cellular respiration
•  The citric acid cycle,
or Krebs cycle, is
the cyclical process
that breaks down
the citric acid by a
series of reaction
Citric acid cycle/Krebs cycle
•  The citric acid cycle
produces more ATP,
as well as some
GTP (a high-energy
molecule similar to
ATP).
•  More high-energy
electrons are
released, forming
NADH from NAD+
•  The last phase of
cellular respiration is
the electron
transport chain,
which occurs on the
inner mitochondrial
membrane
Electron transport chain
•  In this phase, the NADH
releases the highenergy electrons it
picked up during
glycolysis and the citric
acid cycle
•  The energy from these
electrons is used to
convert large quantities
of ADP into ATP
Electron transport chain
•  The electrons
transfer through a
series of carrier
proteins and they
eventually pass on
to oxygen,
converting it to water
•  Each electron
transfer releases
energy
Chemosynthesis
•  The process by
which inorganic
chemicals are
broken down to
release energy
Chemosynthesis
•  The only known
organisms that are
able to carry out
chemosynthesis are
bacteria
Chemosynthesis
•  These organisms form
the base of the food
chain around thermal
vents found on the
ocean floor
•  These organisms are
also found around other
aquatic volcanic vents
like found around
Yellowstone National
Park
Chemosynthesis
•  Chemosynthetic
bacteria can oxidize
sulfates or ammonia
to produce two free
electrons
•  The two free
electrons are used
to fix carbon dioxide
into carbohydrates
Chemosynthesis
•  This process is
similar to the way
that green plants
utilize light energy
and carbon dioxide
to produce
carbohydrates
•  These bacteria are
an important part of
the nitrogen cycle
•  Some of these bacteria
are well specialized to
conditions that would
have existed on the
early Earth, leading
some scientists to
hypothesize that these
are living
representatives of the
earliest life on Earth
Photosynthesis
•
•
•
•
•
Function: Energy storage
Location: Chloroplasts
Reactants: CO2 & H2O
Products: C6H12O6 & O2
Chemical Equation:
6CO2 + 6H2O -> C6H12O6 + 6O2
Cellular Respiration
•
•
•
•
•
Function: Energy release
Location: Mitochondria
Reactants: C6H12O6 & O2
Products: CO2 & H2O
Chemical Equation:
6O2 + C6H12O6 -> 6CO2 + 6H2O
Chemosynthesis
•  Function: Energy storage
•  Location: Prokaryotic cells
•  Reactants: CO2 + H2O + O2 + sulfate or
ammonia
•  Products: carbohydrates & varied acids
•  Chemical Equation: varies
Anaerobic Respiration
•  Anaerobic
respiration, or
fermentation is the
process by which
sugars break down
in the absence of
oxygen
•  The process of
cellular respiration
described earlier is
called aerobic
respiration, which is
the break down of
sugar in the
presence of oxygen
•  Our muscle cells,
fungi, and some
bacteria are capable
of carrying out
anaerobic
respiration
•  These cells convert
the products of
glycolysis into either
alcohol or lactic acid
•  Glycolysis releases energy, while the
production of alcohol or lactic acid
provides NAD+, the electron carrier
needed for glycolysis
Alcoholic fermentation
•  Yeast and some
bacteria can carry
out alcoholic
fermentation
Alcoholic fermentation
•  Yeast produce
ethanol (C2H6O)
through a process
called alcoholic
fermentation
•  Carbon dioxide gas
is released during
alcoholic
fermentation
Alcoholic fermentation
•  This carbon dioxide
gas is responsible
for the holes in
bread
•  Yeast is commonly
put in bread to make
it rise
Alcoholic fermentation
•  During alcoholic
fermentation the
yeast produces
carbon dioxide,
which becomes
trapped in the
dough, forming
small bubbles and
causing the bread to
rise
Alcoholic fermentation
•  Carbon dioxide
produced by yeast in
beer gives the beer
its bubbles
•  Other uses of
alcoholic
fermentation are the
making of bread,
beer, wine, and
liquor
Lactic acid fermentation
•  Animal cells cannot
perform alcoholic
fermentation
•  Instead, they
produce lactic acid
from the products of
glycolysis, through
the process of lactic
acid fermentation
Lactic acid fermentation
•  Human muscle cells
produce lactic acid
during strenuous
exercise
•  During strenuous
exercise, a person
cannot take in enough
oxygen through
breathing to supply all
the muscles with the
necessary oxygen
Lactic acid fermentation
•  As a result, lactic
acid fermentation
occurs to supply the
muscles with the
needed energy
Lactic acid fermentation
•  During and after
intense physical
activity, muscles are
sore due to the
presence of lactic
acid
Lactic acid fermentation
•  Some bacteria use
lactic acid
fermentation to
obtain food energy
Lactic acid fermentation
•  Bacteria that can
convert lactose into
lactic acid are used
to make yogurt and
cheeses
•  The presence of the
lactic acid gives
yogurt and some
cheese a sour taste