Anaerobic Respiration

• Cellular respiration requires O2 to produce
• Glycolysis can produce ATP with or
without O2
What happens if oxygen is not available?
In the absence of O2 glycolysis
couples with fermentation to produce
Fermentation and Cellular
Respiration Compared…
• Both use glycolysis to break down glucose
to pyruvic acid
• Cellular respiration produces much more
• Enables some cells to produce ATP
without the use of oxygen
• Produces a limited amount of ATP from
glucose without an ETC (electron transport
• Produces ethyl alcohol or lactic acid
Two common types:
1. Alcoholic fermentation
2. Lactic acid fermentation
Alcohol Fermentation
• Pyruvic acid is converted to ethanol in two
steps, releasing CO2
• Example:
- yeast used in brewing,
winemaking and baking
Lactic Acid Fermentation
• Pyruvic acid is reduced to NADH forming
lactate as an end product with no release
of CO2
• Examples:
- used by some fungi
and bacteria to make
cheese and yogurt
-human muscle when
O2 is scarce
Fermentation in Human Muscle Cells
• Human muscle cells can make ATP with and
without oxygen
– They have enough ATP to support activities
such as quick sprinting for about 5 seconds
– A secondary supply of energy (creatine
phosphate) can keep muscle cells going for
another 10 seconds
• (That’s why some power athletes consume large quantities of
– To keep running, your muscles must generate
ATP by the anaerobic process of fermentation
When you exercise:
– Muscles need energy in
order to perform work
– Your cells use oxygen to
release energy from glucose
– If you exercise too hard, your
muscles shut down from a lack
of oxygen
– Without enough oxygen, muscle
cells break down glucose to
produce lactic acid
– Lactic acid causes the “burn”
associated with heavy exercise
– Lactic acid is toxic. So if too much
lactic acid builds up, the body lets
you know through pain – the “burn”
• Physical conditioning allows your
body to adapt to increased
• The body can increase its ability
to deliver oxygen to muscles
• Lactic acid starts to accumulate in
the muscles once you start
operating above your anaerobic
threshold. This is normally
somewhere between 80% and
90% of your maximum heart rate
(MHR) in trained athletes.
• Runners need to complete long runs to develop the
aerobic capacity
• This happens by means of capillarisation (formation of
more small blood vessels, thus enhancing oxygen
transport to the muscles)
• This creates greater efficiency in the heart and lungs.
• If the aerobic capacity is greater, it means there will be
more oxygen available to the working muscles and this
should delay the onset of lactic acid at a given work