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Respiration
OL
Respiration
Def: Respiration is the enzyme-controlled release of energy from food
that takes place inside cells.
Aerobic Respiration
Def: Aerobic respiration is the release of energy from food which
requires the presence of oxygen.
Explanation of the role of aerobic respiration.
Aerobic respiration occurs in two stages:
Stage 1
This takes place in the cytoplasm. It does not use oxygen. It releases
a small amount of energy .At the end of this stage, glucose has been
broken down into two molecules of pyruvate.
Stage 2
This stage takes place in the mitochondria. This stage uses oxygen.
The two molecules of pyruvate go into the mitochondria and are
broken down to carbon dioxide and water. These reactions release a
large amount of energy.
Equation
C6H12O6 +
6O2
–-> 6CO2 + 6H2O + energy
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Anaerobic respiration
Def: Anaerobic respiration is the release of energy from food, which
does not require the presence of oxygen.
Equation
C6H12O6
–-> Ethanol + 6CO2 +
energy
[Plants, Fungi]
OR
C6H12O6
–-> Lactic Acid + energy
[Animals, Bacteria]
Fermentation
 Fermentation is the breakdown of carbohydrates in the absence
of oxygen.
 Natural fermentations are used to improve the flavour of foods
and to preserve them.
 Industrial fermentation is the breakdown of carbohydrates by
micro-organisms in the presence or absence of oxygen.
 Fermentation is involved in the production of beer, bread,
coffee beans, wine and yoghurt.
 Two common fermentations are lactic acid fermentation by a
range of bacteria to make yoghurt, and alcoholic fermentation
by yeast.
 Fermentation of alcohol can also take place in bioreactors
containing immobilised yeast cells.
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Respiration
HL
Respiration takes place in two stages:
Stage 1
 This stage is called glycoysis.
 It takes place in the cytoplasm (cytosol).
 It produces just a small amount of energy as ATP.
 If fermentation takes place, the molecules of pyruvate change
to ethanol + CO2 (yeast) or to lactic acid (bacteria and humans)
Stage 2
 This stage is known as the Krebs cycle.
 It stage takes place inside the mitochondria.
 The pyruvate goes into the mitochondria and becomes
broken down in steps by the removal of CO2 and H
atoms.
 Pyruvate changes to Acetyl Co-A + CO2 .
 Acetyl Co-A joins a sequence of reactions that releases H
atoms and CO2 .
 The H atoms are picked up by an H carrier which is
situated on the inner membrane of the mitochondria.
 The energy of the electrons is used to make ATP.
 At the end of the electrons carriers the electrons combine
with the H+ ions and with O atoms to form H2O.
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