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UNIT V – THE WORKING CELL PART II
I. CELLULAR RESPIRATION - _AEROBIC_ ENERGY PRODUCTION
(pp. 221-223, 226-229)
Cellular respiration is the breakdown of _glucose__ in the presence of
_oxygen___ to “make” _ATP__. The oxygen required for cellular
respiration is _inhaled___ into the _lungs_, _diffuses___ into the _blood___,
and is delivered to the _mitochondria_ of the body cells by _red blood
cells__. The glucose needed is obtained through _eating/digestion_. The
glucose is transported in the blood and enters the body cells via
_facilitated diffusion._
O2
There are two major parts to cellular respiration:
A. Glycolysis – Means _”sugar-breaking”__. Occurs in the _cytosol__ of
the cell. Glycolysis does not require _oxygen_. The splitting of glucose, or
glycolysis, occurs very quickly with the aid of _enzymes_, producing two
_3_ -C molecules known as _pyruvic acid_.
In addition, when the bonds of glucose are broken, the high energy electrons
that are released are caught by _NAD+ NADH, a molecule that acts as an
electron carrier. This electron energy will be converted to ATP later in the
process.
Glycolysis requires _2_ ATP to occur, but results in the formation of _4_ ATP,
for a net _gain_ of _2_ ATP.
 Reaction: C6 H12 O6 + 2 ATP → 2 pyruvic acid + 4 ATP +NADH
 Net Gain of ATP = __2 ATP__
B. Oxidative Respiration – Glycolysis releases less than ¼ of the chemical
energy stored in glucose. Most of its potential energy remains bound in the
_pyruvic acid_ formed from glycolysis. In aerobic conditions, meaning
_O2__ is available, the pyruvic acid formed from the breakdown of
_glucose__ during _glycolysis__ enters the _mitochondria___ of the cell
where the _enzymes__ of oxidative respiration complete the breakdown of
glucose to produce _carbon dioxide__, _water___, and _34 ATP___.
 Reaction: __2 pyruvic acid + O2 → CO2 + H2O + 34 ATP___
 Net Gain of ATP = __34 ATP___
Oxidative respiration is a 2-part process:
1. Krebs Cycle – series of reactions that occur in the mitochondrial matrix,
in which the energy stored in _pyruvic acid___ is released in the form of
high-energy _electrons___ when covalent bonds are broken and pyruvic
acid is completely broken down to _C, H, O_. There are only _2_
additional ATP produced in the Krebs Cycle; most of the energy released is
captured in the form of electron energy, producing additional _NADH_. In
addition, a second type of electron carrier is utilized, producing 2 “filled”
___electrons (FADH2)__________.

Net Energy Gain = _NADH, FADH2, 2 ATP____
2. Electron Transport Chain – In this step, the electron carriers, _NADH__
and _FADH2_ “dump” their electrons. These electrons are passed along a
series of molecules embedded in the inner membrane of the
_mitochondria_ of _eukaryotic_ cells. This same process occurs in the
_cell membrane_ of _prokaryotic_ cells. As the electrons “fall” down the
ETC, the energy they release is used to power an enzyme known as
_ATP synthase_, which attaches phosphate groups to _ADP_ to produce
_ATP_. This process is known as _oxidative phosphorylation_because
_oxygen_ must be present. It is the _protons_ of oxygen that “pulls” the
electrons down the ETC. As the electrons are collected by oxygen, _H2O_
is produced.
 Net Energy Gain = _32 ATP
http://www.dnatube.com/video/2354/Electron-Transport-Chain
*Combined Reactions of Glycolysis + Oxidative Respiration = Cellular Respiration*
____ C6 H12 O6 + 6O2 → 6CO2 + 6H2O + 36 ATP_________
**TOTAL ATP YIELD PER MOLECULE OF GLUCOSE**
Glycolysis = __2_ ATP
Krebs Cycle = __2_ ATP _
ETC =
32 ATP_
II. FERMENTATION - __ANAEROBIC_ ENERGY PRODUCTION (pp. 223, 224)
Glycolysis is constantly occurring in the _cytosol__ of every cell under
_anaerobic___ conditions, meaning _oxygen__ is not required. The reaction
for glycolysis is: _ C6 H12 O6 + 2 ATP → 2 pyruvic acid + 4 ATP +NADH _
Glycolysis is the first step for all cellular energy production.
 If oxygen is available, _oxidative respiration_ follows glycolysis.
Pyruvic acid is broken down to _CO2_and H2O and 36 ATP are
produced.
 If oxygen is not available, some types of cells have a back-up
mechanism for glucose metabolism called _fermentation___. If a
cell cannot switch to fermentation, it cannot survive without oxygen.
A. General Description
In fermentation, the pyruvic acid formed during glycolysis does not enter
the _mitochondria_, instead, the entire pathway takes place in the
_cytosol____. Fermentation does not produce any additional _ATP__,
but the removal of pyruvic acid from the cytosol allows the process
of glycolysis and the net gain of _2__ATP to continue.
B. Types of Fermentation - The 2 most common fermentation pathways used
by cells are:
1. Lactic Acid Fermentation – Pyruvic acid is converted to _lactic acid_.
May be utilized by:
 Human Muscle Cells – Occurs when demand on muscles exceeds
supply of oxygen. As lactic acid builds up in the muscle cells, it is felt
as _pain and fatigue__. This is referred to as _oxygen debt___. As
activity slows, and oxygen is re-supplied, the muscle cells switch back
to _cellular respiration___ and the lactic acid is sent to the _liver_ to
be broken down.
 Bacteria & Fungi – There are some types of bacteria & fungi that carry
out lactic acid fermentation in _anaerobic__ conditions. This is utilized
by the dairy industry to produce _cheese__ and _yogurt___.
C6 H12 O6 + 2 ATP → 2 pyruvic acid + 4 ATP → lactic acid___
2. Alcoholic Fermentation – Pyruvic acid is converted to _alcohol__ and
_CO2___. When oxygen supplies are depleted, _yeast__ and many
bacteria switch to alcoholic fermentation. This process is used commercially
for _brewing and baking________
_ C6 H12 O6 + 2 ATP → 2 pyruvic acid + 4 ATP → alcohol + CO2__
**TOTAL ATP GAIN IN FERMENTATION = 2 ATP **
III. ENERGY FLOW – A COMPARISON OF PHOTOSYNTHESIS &
CELLULAR RESPIRATION (p. 232)
PHOTOSYNTHESIS
CELLULAR RESPIRATION
Function
Capture energy
Release energy
Cell
Location
Chloroplasts
Mitochondria
Occurs In
Autotrophs
Heterotrophs AND Autotrophs
Reactants
CO2 + H2O + energy
C6 H12 O6 + O2
Products
C6 H12 O6 + O2
CO2 + H2O + energy
Overall
Reaction
CO2 + H2O +energy → C6 H12 O6 + O2
C6 H12 O6 + O2 → CO2 + H2O + energy
Suggested Study Questions
p.237 (1 – 15, 18)