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Biology II – Chapter 8: Cellular Respiration
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The metabolic process that harnesses the energy in organic compounds and turns them
into usable energy called ATP.
The primary fuel for cellular respiration is glucose.
Oxygen is required for ATP production.
Carbon dioxide is released as a by-product.
The conversion of glucose and oxygen into carbon dioxide, water, and energy in the form
of ATP
Occurs in the mitochondria of the cell.
o Matrix – fluid contained in the inner compartment – Krebs cycle occurs here
o Cristae – Intermembrane compartment (between the inner and outer membrane) –
electron transport occurs here
C6H12O6 + 6O2
glucose
+ oxygen
gas
enzymes
=
6CO2 + 6H2O + energy
carbon
dioxide
+ water
+
ATP
energy

Cellular Respiration occurs in 2 stages:
o Glycolysis – glucose is broken down.
o Presence of oxygen determines the 2nd stage:
 Aerobic – oxygen present – Cellular Respiration – large amount of ATP is
made
 Anaerobic – oxygen absent – Fermentation – alcohol or lactic acid is made
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Glycolysis (1st Stage of Cellular Respiration)
o Takes place in the cytoplasm – does not require oxygen
o Not necessary for aerobic cellular respiration, even though it plays a role in it.
o Glucose (beginning product) is broken down and converted into 2 pyruvate (end
product) – producing small amounts of ATP and NADH that enters the
mitochondria
o Each Pyruvate is then split into CO2 (by-product) and two-carbon acetyl group
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Krebs Cycle (2nd Stage of Cellular Respiration)
o Begins and ends with citric acid
o Occurs in the matrix
o If Oxygen is present:
 Aerobic Cellular Respiration occurs:
 Pyruvate and NADH are used to make a large amount of ATP.
o Occurs in the mitochondria of Eukaryotic cells.
o Occurs in the cell membrane of Prokaryotic cells.
o If Oxygen is not present:
 Fermentation occurs:
 Pyruvate is converted into lactate or ethanol (alcohol) and carbon
dioxide (CO2); additional ATP is not generated.
o Lactate – (lactate fermentation) – animal cells – cells
deprived of oxygen produce lactic acid instead of pyruvate;
once oxygen is available lactic acid turns back into
pyruvate
o Ethanol (alcohol) and CO2 – (alcoholic fermentation) –
yeast cells – produces/gives off CO2 and alcohol is
evaporated
Advantages
Animal Muscle cells are able to
cells
produce ATP when oxygen
is limited due to vigorous
work
Yeast
Yeast cells are capable of
cells
growing and dividing when
oxygen is limited
Disadvantages
Lactate will begin to build up and
cause muscle fatigue where they
no longer contract
The alcohol they produce
eventually kills them if the initial
glucose levels are high

Electron Transport Chain
o Occurs in the inner compartment (the cristae) of the mitochondria.
o Hydrogen ions are pumped out of the inner compartment of the mitochondria.
o Hydrogen accumulates in the outer compartment – producing the concentration
gradient.
o Chemiosmosis takes place and a large amount of ATP is produced as hydrogen
diffuses into the inner compartment through a channel protein.
o At the end of the transport system, hydrogen combines with oxygen to form water
(H2O).
 Oxygen is the final electron acceptor.
Glycolysis
ATP Produced per Glucose Molecule
Direct
By Way of Electron
Transport System
2 ATP
2 NADH2 =
6 ATP
Transition Reaction
Krebs Cycle
Subtotals
Grand Total

2 ATP
2 NADH2
=
6 ATP
6 NADH2
=
18 ATP
2 FADH2
=
4 ATP
34 ATP
4 ATP
38 ATP
Harvesting Energy – Glycolysis and Cellular Respiration/Fermentation:
Glucose
Stage 1 –
Glucose is
broken down to
pyruvate.
NAD
ADP
NADH2
ATP
Stage 1
Pyruvate
Anaerobic
(without O2)
Fermentation
Ethanol (alcohol)
and CO2
or
lactate
Stage 2
Aerobic
(with O2)
Respiration
Mitochondrion
Stage 2 –
The presence of O2
determines whether
aerobic respiration or
fermentation will occur.
ATP
H2O
Aerobic Cellular Respiration versus Photosynthesis
Aerobic Cellular
Photosynthesis
Respiration
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Mitochondrion
Chloroplast
Releases energy
Requires energy
Requires O2
Releases O2
Releases CO2
Requires CO2
Comparison of Aerobic Respiration & Photosynthesis
o Both use a hydrogen carrier
 Aerobic cellular respiration – NAD
 Photosynthesis – NADP
o Both use an electron transport system located in membranes to generate ATP
o Both occur in daylight hours
 Only aerobic cellular respiration occurs at night
o Plant and animal cells carry on aerobic cellular respiration
 Only plant cells carry on photosynthesis
o Photosynthesis is the build up of glucose
o Aerobic cellular respiration is the break down of glucose
o The overall equation for both are opposite each other:
photosynthesis
energy + 6 CO2 + 6 H2O
C6H12O6 + 6 O2
aerobic cellular
respiration