Anaerobic Respiration
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Releasing energy
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How do cells get their energy?
All organisms need energy
to survive.
Animals obtain their energy
from the food they eat, but
plants can make their own
food by photosynthesis.
In both cases, however,
energy must first be converted
into a form that can easily be
used by cells. This process is
called respiration.
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What is anaerobic respiration?
Aerobic respiration uses oxygen to break down glucose.
It releases a lot of energy from each glucose molecule by
breaking it down completely into carbon dioxide and water.
Anaerobic respiration takes
place without oxygen.
Less energy is released per
glucose molecule than in aerobic
respiration because glucose is
only partially broken down.
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Respiration in animals
When an animal cell is getting enough oxygen and
glucose, it carries out aerobic respiration.
glucose
+
oxygen 
carbon
dioxide
+
water ( + energy)
When the animal cell does not have the necessary oxygen
to break down glucose molecules, it has to carry out
anaerobic respiration. This can occur in muscle cells
during strenuous exercise.
glucose  lactic acid ( + energy)
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Respiration in plants and micro-organisms
Plants and some micro-organisms, such as yeast, will also
carry out anaerobic respiration if necessary.
Anaerobic respiration might take place
in waterlogged root cells, or in bacteria
infecting deep puncture wounds.
The products of anaerobic respiration are
different in plants than in animals.
glucose  carbon dioxide + ethanol (+ energy)
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When does anaerobic respiration occur?
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Lactic acid
The incomplete breakdown of glucose during anaerobic
respiration produces lactic acid.
Lactic acid builds up in muscle cells and
prevents the muscles from contracting
efficiently. The build-up of lactic acid can
cause fatigue, pain and cramping.
After vigorous exercise, the body needs to remove lactic
acid before it damages cells. Some lactic acid is broken
down in the muscles. Some passes into the bloodstream
and is taken to the liver to be broken down there.
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Oxygen debt
Oxygen is needed to break lactic acid into water and
carbon dioxide.
Following strenuous exercise, an
individual breathes heavily and
maintains an elevated heart rate.
This moves lactic acid to the liver
and supplies liver and muscle cells
with the necessary oxygen to break
down lactic acid.
The amount of oxygen needed to break down lactic acid
remaining after exercise is called excess post-exercise
oxygen consumption (EPOC), or an oxygen debt.
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How does running affect your pulse?
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Complete the sentences
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Micro-organisms in industry
Respiring micro-organisms are used in the commercial
production of many different products, including:
 bread
 alcohol
 biofuels.
These micro-organisms break substances down using
aerobic or anaerobic respiration. The effect of anaerobic
respiration is often called fermentation.
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Yeast in bread production
Yeast is a type of fungus used in
bread production. Yeast digests the
carbohydrates in flour, producing
carbon dioxide.
This carbon dioxide causes bread
to rise. It also creates gas pockets
in the dough, giving baked bread a
spongy texture.
At first the yeast respires aerobically,
but once it uses up the available oxygen
it begins to respire anaerobically.
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Yeast in the production of alcohol
Yeast is used to make alcoholic beverages such as beer,
wine, rum, whiskey and vodka.
During fermentation, anaerobic respiration in yeast cells
converts glucose into ethanol.
The amount of ethanol
produced is limited as alcohol
becomes toxic to microbes at
certain concentrations.
Glucose comes from different sources in the production of
different alcohols. For example, in winemaking, natural
sugars in the grapes form the energy source for yeast.
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Anaerobic respiration in biogas
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Anaerobic respiration equations
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Glossary
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Multiple-choice quiz
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