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Summary A Level Biology OCR A - Anaerobic Respiration (18.5)
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OCR Biology B Module 2 Summary
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☀18.5 Anaerobic
Respiration
Class Bio
Created @Apr 17, 2021 2:18 PM
Date of Exam @Apr 26, 2021
Exam Questions done?
Reviewed
Teacher Mrs Batchelor
Type Sub-topic
Aerobic respiration was not possible when life began, as there
was little oxygen present in the atmosphere of the Earth at
that time. It is a relatively new process in evolutionary
terms but as it is a far more efficient process than anaerobic
respiration it was rapidly selected for. Aerobic respiration
produces around 38 molecules of ATP per glucose molecule
whereas fermentation only produces two molecules of ATP (net).
18.5 Anaerobic Respiration 1
, anaerobic respiration in
eukaryotic organisms
Eukaryotic cells respire aerobically if enough oxygen is
available. Anaerobic respiration, resulting in the synthesis
of smaller quantities of ATP, occurs in the absence of oxygen
and is also used when oxygen cannot be supplied fast enough to
respiring cells. The use of this less efficient process to
produce ATP is a temporary 'emergency' measure to keep vital
processes functioning.
Organisms fall into different categories determined by their
dependence on oxygen or not:
obligate anaerobes - cannot survive in the presence of
oxygen. Almost all obligate anaerobes are prokaryotes,
although there are some fungi too.
facultative anaerobes - synthesise ATP by aerobic
respiration if oxygen is present, but can switch to
anaerobic respiration in the absence of oxygen e.g. yeast.
obligate aerobes - can only synthesise ATP in the presence
of oxygen, for example, mammals. The individual cells of
some organisms, such as muscle cells in mammals, can be
described as facultative anaerobes because they can
supplement ATP supplies by employing anaerobic respiration
in addition to aerobic respiration when the oxygen
concentration is low. However, this is only for short
periods and oxygen is eventually required. The shortfall of
oxygen during the period of anaerobic respiration produces
compounds that have to be broken down when oxygen becomes
available again, so the organism as a whole is an obligate
aerobe.
fermentation
Fermentation (a form of anaerobic respiration) is the process
by which complex organic compounds are broken down into
simpler inorganic compounds without the use of oxygen or the
involvement of an electron transport chain.
18.5 Anaerobic Respiration 2
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