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Cellular Respiration
Vocabulary:
-Glycolysis
-Kreb’s Cycle
-Pyruvic acid
-Fermentation
-Aerobic Reaction
-Anaerobic Reaction
Review
• What is photosynthesis?
• Where does this occur?
• What is the difference between ATP and
ADP?
• What is the difference between NADPH
and NADP+?
• Light vs. Dark reactions
• After glucose is made in photosynthesis,
how is the energy in the sugar molecules
released so it can be used by the
organism?
– cellular respiration!
• Cellular Respiration occurs in both plant
& animal cells
– WHERE????
– CYTOPLASM &
MITOCHONDRIA!!!
The Power House of the Cell!!
Cellular Respiration…
A Controlled Process
• Food (glucose), like fuel, is "burned"
by our cells for energy
– if it's burned all at once, too much
energy is released
• therefore, the reaction is broken
down into many small steps controlled
by ENZYMES
– Cells gradually release the energy from
glucose and other compounds
• the energy is transferred to the
bonds of ATP which stores and
releases the energy in usable amounts
to be used by the cell
• energy is stored in bonds between
phosphate groups
AMP
ADP
P
P
ATP
Cellular Respiration
• Process that releases ENERGY by
breaking down food molecules in the
presence of oxygen
• Occurs in both plants and animals
Cell respiration occurs in 3 stages:
• Glycolysis
• Citric (Krebs) cycle
• Electron transport chain
Glycolysis
(glyco= sugar, lysis = breaks down)
• Process occurs in the cytoplasm
• Breaks glucose down from 6-carbon
compound into two 3-carbon compounds
(called pyruvate)
Equation:
C6H12O6
enzymes in
cytoplasm
2 pyruvates + 2 ATP
• Glycolysis can occur if oxygen is present
(aerobic) or absent (anaerobic)
– Glycolysis is ALWAYS the first step
in breaking down glucose
• If oxygen IS present, then cells
proceed with Respiration/Krebs
• If oxygen is NOT present, then cells
ferment
Cellular Respiration can be
broken down into 2 processes:
1) Glycolysis: breaking down glucose
2) Respiration (Krebs Cycle & Electron
Transport Chain): uses oxygen to
finish breaking down products from
Glycolysis & release energy
GLUCOSE
CO2
H2O & heat
energy
O2
Glucose + Oxygen
Carbon Dioxide + Water
C6H12O6
6CO2
+
6O2
Look familiar???
+
6H2O
Respiration/Krebs
• Occurs in the Mitochondria of cell
• Only if oxygen is PRESENT (aerobic)
• Uses the pyruvic acid from glycolysis to
produce carbon dioxide, water, and ATP
• Products:
– 34 ATP per molecule of glucose
– carbon dioxide
– water
So how does this happen?
• The Citric (Krebs) cycle and the electron
transport chain turn the pyruvate into CO2,
H2O, and ATP
• To do this, pyurvate loses a carbon atom
to make Acetyl CoA
• Acetyl CoA enters the Krebs Cycle to
produce CO2, NADH, and FADH2
• The NADH and FADH2 carry energy to the
electron transport chain to make more ATP
(this requires oxygen)
C6H12O6 + 6O2
6 CO2 + 6 H2O + 36 ATP
Summary of Cellular Respiration
GLYCOLYSIS
“break sweetness”
Location in the
cell:
It starts with:
It ends with:
Is Oxygen
required?
# of ATP’s
Produced:
RESPIRATION/
Kreb’s Cycle
Cytoplasm
Mitochondria
C6H12O6
(glucose)
2 (C3H6O3)
pyruvic acid
NO
2 pyruvic acid
2 (tiny)
H2O, CO2, ATP
YES! 
AEROBIC
34 (lots!)
GRAND TOTAL= 36 ATP!!
• 2 are produced in Glycolysis and 34 in
Respiration/ Kreb’s Cycle
– 18 times more ATP are produced in the
presence of Oxygen!!
How efficient is this??
• The 36 ATP molecules
the cell makes per 1
glucose represents
about 38% of the total
energy in glucose
• Even though it doesn’t
seem like much, this is
more efficient than your
car’s gas burning
engine
• What happens to the
remaining 62%???
– It is released as heat.
What happens if your cells
aren’t getting enough oxygen?
• Respiration/Kreb’s CANNOT proceed
• Fermentation occurs
– Pyruvic Acid builds up in animal muscle cells as
LACTIC ACID… feel the burn!
– In other organisms, the pyruvic acid builds up,
ferments, and becomes alcohol
• Fermentation: release of energy from food
molecules in absence of oxygen (anaerobic)
• Enables cells to carry out energy
production in the absence of Oxygen
• result of glycolysis + fermentation yields 2
ATP molecules per 1 molecule of glucose
(not nearly as much energy!!!!)
2 Fermentation Pathways:
1.Lactic Acid
Fermentation:
• pyruvic acid from
glycolysis is converted
to lactic acid
• lactic acid is produced
in muscles during rapid
exercise (body can't
supply enough O2 to the
tissues)
• the build-up of lactic
acid causes a burning,
painful sensation in your
muscles
Energy & Exercise: Quick Energy
• Muscle cells only contain enough ATP for a
few seconds of “burst” energy
– emergency, starting gun of race
• When this is gone, cells resort to lactic
acid fermentation which can provide
enough ATP for about 90 seconds
Long Term Energy
• If a race or energy need is longer,
your body must go through
cellular respiration to get enough
ATP to continue
– Even well-conditioned athletes have
to pace themselves
– Your body stores energy in muscle
• glycogen
– these stores are enough to last for
15-20 minutes of activity when
broken down through cellular
respiration
– After this, your body begins to
break down fats and other stored
molecules
2. Alcoholic Fermentation:
• Occurs in yeast cells &
some other
microorganisms
• Pyruvic acid is broken
down into a 2-Carbon
alcohol plus carbon
dioxide
Alcoholic Fermentation
• Important to brewers & bakers!
– When yeast in dough runs out of oxygen
it ferments, giving off bubbles of carbon
dioxide gas—which forms air space in
bread
– Alcohol produced in the dough
evaporates when bread is baked
*(when the level of alcohol reaches
12%, yeast cells die)