· Respiratory substrate is the
organic food material which is used for respiratory breakdown. It can be
carbohydrates, organic acids, proteins, fats or oils.
· Glucose is the readily
available energy source for the cells.
· Oxidation of the substrate
during anaerobic respiration is incomplete. The by products are ethyl
alcohol, CO2 and energy released.
· Mitochondria are the cell
organelles concerned with aerobic respiration and are present in eukaryotic
cells only. They are called power houses of the cell.
· Yeast, i.e. Saccharomyces,
is the unicellular fungus that releases enzyme zymase that brings about
· Lactic acid fermentation is
due to microorganisms like lactic acid bacteria. During lactic acid
fermentation lactose is broken down to lactic acid. CO2 is not
evolved in this process.
· ATP is adenosine
triphosphate. Each ATP molecule is composed of pentose sugar ribose, purine
base adenine and three phosphate groups. Adenine and ribose form adenosine.
The three phosphate groups attached to adenosine in a chain form ATP. Of the
three phosphate bonds, maximum energy is stored in the third or last
phosphate bond. The third phosphate bond breaks on hydrolysis of ATP and
releases approximately 7.3 kcal of energy.
+ 7.3 kcal + iP
· Respiratory quotient, i.e. R.Q,
is a respiratory ratio of the volume of CO2 liberated to the
volume of O2 absorbed during respiration.
Volume of Co2
Volume of O2
It is measured by using respirometer.
· The R.Q. value differs
depending on the type of respiration, complete or incomplete oxidation of
substrate and nature of respiratory substrate.
· For carbohydrates, the
R.Q. is one because the volume of CO2 released during respiration
is equal to volume of O2 absorbed. Example: Seeds of rice, wheat,
oat, pea, etc.
· For oils and fats the
R.Q. is less than one because the oxygen content of fats and oils and is very
less. Thus, they need more oxygen during respiration, while the CO2
released is less. Thus the R.Q. is less than oneand is mostly around 0.7.
Example: Mustard seeds, castor seeds, etc.
· R.Q. for proteins is
also less than one approximately 0.8 or 0.9.
· For organic acids like
oxalic acid, the R.Q. is more than one because the oxygen content of organic
acids is higher. Thus, oxygen required for respiration is less and the volume
of CO2 released is more.
· During anaerobic
respiration, the value of R.Q. is infinity because it takes place without
oxygen but CO2 is released.