South Tuen Mun Government Secondary School
Biology Revision Note 17
Respiration - is the process by which energy is given out
Aerobic respiration - the release of energy using oxygen
- take place in nearly ALL living organisms
Glucose + oxygen
carbon dioxide + water [overall reaction]
(energy is released as heat and it is used to do phosphorylation : ADP + [P]  ATP])
Anaerobic respiration - the release of energy without oxygen
Alcoholic fermentation - takes place in yeast, bacteria, lower organisms, green plants
Glucose  ethanol (alcohol) + carbon dioxide (energy is released as heat and for phosphorylation)
Accumulation of ethanol (alcohol) can kill the living organisms.
Lactic acid fermentation – takes place in skeletal muscle of man / mammal and some bacteria
 Heavy exercise increases the energy demand of skeletal muscle. The rate of aerobic respiration increases.
Aerobic respiration requires glucose and oxygen. When the highest rate and depth of breathing cannot provide
enough oxygen to meet the energy demand, lactic acid fermentation takes place (at the same time with
aerobic respiration) to supply extra energy to the skeletal muscle.
Glucose  lactic acid (energy is released as heat and for phosphorylation)
Accumulation of lactic acid will lead to fatigue of skeletal muscles. After heavy exercise, lactic acid is removed:
Lactic acid + oxygen  carbon dioxide + water

energy

lactic acid  glucose  glycogen
Therefore oxygen is used to remove lactic acid. The amount of oxygen required to remove lactic acid is called
oxygen debt.
Biochemical pathway of aerobic respiration:
(I)
Glycolysis – the splitting of glucose (6-C compound) into 2 x 3-C compound
The products of glycolysis are pyruvate (3-C compound), ATP
and NADH. The process of glycolysis does not need oxygen.
(II)
Krebs cycle
(1) the change of _____________________ into acetyl-CoA (2-C) [this is not a part of the Krebs cycle]
The products are NADH, acetyl-CoA, CO2 (carbon
dioxide).
(2) Krebs cycle
The products are CO2, NADH, FADH,
ATP and regeneration of coenzyme A.
(III)
Oxidative phosphorylation
In oxidative phosphorylation, NADH and FADH will move the hydrogen atoms through different hydrogen
carriers. Eventually, hydrogen is accepted by oxygen to form water (H2O). Energy is given out to form ATP. 1
NADH is used to make 3 ATP, 1 FAD makes 2ATP. As a conclusion, in aerobic respiration, a total of 38 ATP is
produced.
Biochemical pathway of anaerobic respiration:
(i)
Alcohol fermentation
In alcohol fermentation, pyruvate accepts hydrogen from NADH to make ethanol and gives out carbon
dioxide. A total of 2 ATP is produced.
(ii)
Lactic acid fermentation
In lactic acid fermentation, pyruvate accepts hydrogen from NADH to make lactic acid. A total of 2 ATP is
produced.
Structure of mitochondrion:
Function of :
Outer membrane – control the passage of
substances in and out of the mitochondrion;
Inner membrane – highly folded to carry more
enzymes for oxidative phosphorylation.
Matrix – contains enzymes to carry out the
chemical reactions of the Krebs cycle.
Daily application of anaerobic respiration:
 Brewing of beer + making wine [alcohol fermentation produces ethanol / alcohol in the drink]
 Making bread [alcohol fermentation to make carbon dioxide that produces pores in the bread  soft]
 Making yoghurt [lactic acid fermentation produces lactic acid to give the sour taste of the food]


Making cheese [lactic acid fermentation produces lactic acid to lower pH and coagulate the proteins of dairy
products]
Making biofuel [alcoholic fermentation produces alcohol / ethanol as fuel]
Comparison between aerobic and anaerobic respiration
Similarities:
Both use glucose as a substrate.
Both give out energy to make ATP.
Both are catalysed by enzymes.
Differences:
Aerobic respiration
Anaerobic respiration
takes place in both cytoplasm and mitochondria
takes place in cytoplasm only
requires oxygen
does not require oxygen
produces carbon dioxide, water
produces ethanol / alcohol and carbon dioxide or
produces lactic acid
complete oxidation
incomplete oxidation
more energy released to form 38 ATP
less energy released to form 2 ATP