Chapter 8.3
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Respiration is a process in which living cells
break down glucose and release its stored
energy in the form of ATP
Respiration is necessary for life.
Organisms obtain energy in a process
called cellular respiration.
The equation for cellular respiration is the
opposite of the equation for
photosynthesis.
6. Cell respiration occurs in ALL cells.
7. It begins with glycolysis, and continues with either
anaerobic respiration (AKA fermentation) if oxygen
is absent or aerobic respiration if oxygen is present.
First Stages of Cellular Respiration
Organic Compounds
C6H12O6
ATP
Glycolysis
Oxygen Absent
Fermentation
Oxygen Present
ATP
Aerobic
Respiration
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Occurs in the cytoplasm
Can occur with or without oxygen
Glucose is split into 2 molecules of pyruvic
acid (which is a 3 carbon compound)
In addition to pyruvic acid, 2 molecules of
ATP and 2 molecules of NADH are formed
for each molecule of glucose that is broken
down.
5. End products of glycolysis
a. 2 ATP (makes 4 but uses 2 ATP)
b. 2 molecules of pyruvic acid
c. 2 NADH
d. 2 H2O
6. What happens to the pyruvic acid depends
on:
a. The organism involved
b. presence or absence of oxygen
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Defined as the process of breaking down
pyruvic acid without the use of oxygen
Also called anaerobic respiration
Does not produce ATP
Does produce NAD+ which is reused during
glycolysis
2 forms of fermentation:
a. Lactic acid fermentation
b. alcoholic fermentation
1. Pyruvic acid from glycolysis is converted into a molecule
called lactic acid.
2. Heavy exercise is often the reason for the lack of oxygen
that prevents pyruvic acid from continuing on to aerobic
respiration. This can cause a build up of lactic acid that
results in cramping and muscle soreness.
3. End products of lactic acid fermentation:
a. Lactic acid
b. NAD+ (used in glycolysis)
c. 2 ATP (actually made during glycoysis)
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Occurs in the cytoplasm of some plant cells
and some unicellular organisms such as
yeast under anaerobic conditions
Pyruvic acid from glycolysis is converted to
ethyl alcohol
End products:
a. Ethyl alcohol
b. Carbon dioxide
c. NAD+ (used in glycolysis)
d. 2 ATP (actually made during glycolysis)
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Occurs after glycolysis
Occurs in the mitochondria
Requires the presence of oxygen (aerobic)
3 steps to aerobic respiration
a. Formation of acetyl CoA
b. Krebs cycle
c. Electron Transport Chain
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Pyruvic acid (from glycolysis) enters the
mitochondria through a transport protein
It joins with coenzyme A (CoA) to produce
Acetyl CoA
In the process, NADH is produced
Acetyl CoA can then enter the Krebs cycle
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AKA citric acid cycle
Occurs in the matrix of mitochondria
Discovered by Sir Hans Krebs in 1937
Steps:
a. acetyl enters the cycle to combine with
oxaloacetic acid  citric acid
b. coenzyme A is released to be used again
c. citric acid – carbon dioxide  oxaloacetic
acid (used again)
5. During the cycle, carbon dioxide is released,
NADH and FADH2 are formed, and ATP is
produced
6. End results
a. 6 NADH
b. 4 CO2
c. 2 ATP
d. 2 FADH2
7. The carrier molecules (NADH and FADH2)
transport electrons from the Krebs cycle to
the ETC where water and more ATP are
formed
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Occurs in the inner membrane of
mitochondria
Electrons are donated to the ETC by NADH
and FADH2
ATP is generated by chemiosmosis
The function of oxygen is to act as the final
hydrogen acceptor to produce water
Each NADH produces 3 ATP
Each FADH2 produces 2 ATP
6. The ETC produces
10 NADH  30 ATP
2 FADH2  4 ATP
34 ATP
Glycolysis  2 ATP
Krebs cycle  2 ATP
ETC  34 ATP
*38 ATP from 1 molecule of glucose
-Aerobic respiration is important because it
produces way more ATP than anaerobic
respiration (38 ATP to 2 ATP)