1. The Respiratory Quotient (RQ)
The Respiratory Quotient or RQ value is a measure of the ratio of carbon dioxide
produced and oxygen consumed by an organism per unit time
The respiratory quotient is a ratio and therefore has NO UNITS
volume of carbon dioxide produced
RQ =
per unit time
volume of oxygen consumed
The respiratory quotient is a valuable measurement as it provides us with
information regarding the nature of the substrate being used by an organism
for respiration
The simplified equation for the aerobic respiration of glucose is:
C6H O2 = 6CO H2O
In this reaction, SIX CARBON DIOXIDE MOLECULES are produced and
SIX OXYGEN MOLECULES are consumed
The RQ for this reaction is 6 CO2/6 O2 = 1

2. The Respiratory Quotient (RQ)
The RQ value varies with the nature of the substrate being used for respiration
The following equation represents the complete oxidation of the fatty acid,
OLEIC ACID, when used as the substrate for respiration
The simplified equation for the aerobic respiration of oleic acid is:
2C18H O2 = 36 CO H2O
In this reaction, THIRTY SIX CARBON DIOXIDE MOLECULES are produced
and FIFTY ONE OXYGEN MOLECULES are consumed
The RQ for this reaction is 36 CO2/51 O2 = 0.7

3. The Respiratory Quotient (RQ)
The following table shows the RQ values for different classes of respiratory
substrate when they are used for aerobic respiration
glucose
1.0
fatty acid
0.7
protein
0.9
If any degree of anaerobic respiration occurs RQ values
significantly above a value of 1.0 are obtained

4. MEASURING RESIPRATORY PROCESSES
The RESPIROMETER is a piece of apparatus that can be
used for measuring rates of respiration and RQ values
for small organisms such as woodlice and germinating seeds
The apparatus consists essentially of two boiling tubes
connected by a manometer (capillary U-tube)
Experimental
tube containing
the organisms
to be studied
Control
an equal volume
of glass beads
Manometer U-tube containing
coloured liquid

5. MEASURING RESIPRATORY PROCESSES
A 1 cm3 syringe
is inserted into the
control tube and
is used to force
air through the
apparatus before
the experiment
and to equalise
the manometer
levels between
experiments
Equal volumes of potassium hydroxide (KOH) or
SODA LIME are placed into each of the boiling tubes
The function of the KOH or the SODA LIME is to absorb
CARBON DIOXIDE GAS
The animal or plant material in the experimental tube is
protected from the KOH or SODA LIME by a barrier consisting
of a zinc-gauze platform
The screw clip, when closed, prevents
atmospheric air from entering the apparatus
The scale attached to the manometer
allows changes in the levels of the
manometer fluid to be measured
gauze platform
KOH solution

6. MEASURING RESIPRATORY PROCESSES
The principle behind the functioning of the apparatus is the
changes in AIR PRESSURE within the tubes during the course
of the experiment
As the organisms in the experimental tube respire, they remove
oxygen molecules from the tube and release carbon dioxide
molecules into the tube
The released carbon
dioxide is absorbed
by the KOH solution
The total number
of gas molecules
in the experimental
tube will therefore
be reduced O2
CO2
The air pressure
in the experimental
tube therefore
decreases and the
manometer fluid
will be pushed
upwards in the
left-hand side
of the U-tube

7. The distance moved by the fluid can be measured form the scale
MEASURING RESIPRATORY PROCESSES
The manometer fluid is pushed towards the experimental tube
The distance moved by the fluid can be measured form the scale
distance
moved by
the fluid

8. pr2h MEASURING RESIPRATORY PROCESSES
The volume of oxygen used by the organisms can now be
calculated using the following formula:
pr2h
where
p = (a constant)
r = internal radius of manometer
capillary tube (mm)
h = distance moved by the
manometer fluid (mm)
The control tube
has two functions
Throughout the procedure
the boiling tubes are immersed
in a water bath, usually maintained
at 20°C, to minimise any temperature
fluctuations that may occur during the course of the experiment
It negates any
effects that
temperature
changes may have
on the pressure
of the air in the
system
distance
moved by
the fluid
It enables us
to demonstrate
that any changes
in the manometer
tube are due to
living processes

9. CALCULATING THE RATE OF RESPIRATION
In order to calculate the rate of respiration, other values must be known
The volume of oxygen (mm3) used by the respiring organisms is usually calculated
after a period of ONE HOUR
The mass of the organisms (in grams) used for the experiment is also needed
The rate of respiration is calculated as the
oxygen consumption per gram of body mass per minute
If we had 2g of germinating seeds respiring for one hour in a respirometer and
finally showing a volume change of 20mm3 then:
Rate of respiration = 20
2 x 60
= 0.17
Using the appropriate units then;
Rate of respiration = mm3 g-1 min-1

10. Q10 = The effect of temperature on the respiratory rate
of small organisms can be investigated using
the respirometer
The effect of temperature on the rate of respiration can be
investigated by changing the temperature of the water bath
A temperature range of 10°C to 40°C is suitable for this investigation
As the temperature of the water bath is changed for each rate
measurement, it is important to allow a period of around 10 minutes
to elapse before timing the experiment
This ten minute time period is necessary to allow for equilibration – i.e.
to enable gas pressures in the apparatus to adjust and to allow
the organisms to be fully adjusted to the new temperature
The results of temperature experiments can be used to calculate
a Q10 value for respiration where:
Q10 =
Rate of respiration at toC
Rate of respiration at t + 10ºC

11. pr2h OBTAINING RQ VALUES STEP 1
The respirometer can also be used to obtain values for the
RESPIRATORY QUOTIENT or RQ
As KOH absorbs
carbon dioxide
then the
manometer fluid
will rise towards
the left hand
tube as the
organisms respire
and consume
oxygen
RQ =
volume of carbon dioxide produced
volume of oxygen consumed
per unit time
The apparatus is
first set up with
KOH in the boiling tubes
The distance
moved by the
manometer fluid
is used to calculate
the volume of
oxygen consumed
according to
the formula:
The apparatus is
left to run for one hour
At the end of this
period, a value for
the volume of
oxygen consumed
is obtained
pr2h
KOH solution

12. OBTAINING RQ VALUES STEP 2
The whole procedure is now repeated, under identical
conditions, but with water replacing the KOH solution
Carbon dioxide gas is no longer being absorbed form the air
in the experimental tube
If, under these conditions, the manometer fluid DOES NOT MOVE,
then the volume of oxygen being consumed is EQUAL to the
volume of carbon dioxide being produced
We can conclude
that the volume
of carbon dioxide
produced must
have the SAME
VALUE as the
manometer fluid
did not move
towards either of
the tubes
The volume of
oxygen consumed
in one hour has
been determined
in STEP 1 of the
procedure
Consider this value
to have been
20mm3 of oxygen
in one hour
So volume of
oxygen consumed
is equal to the
volume of carbon
dioxide produced
WATER

13. OBTAINING RQ VALUES STEP 2 RQ = 20 mm3 h-1 = 1
In this example the manometer fluid did not move towards
either of the tubes
Oxygen consumption in one hour is equal to carbon dioxide
production in one hour
Considering the value for oxygen consumption to have been
20mm3 in one hour then:
RQ =
20 mm3 h-1
= 1
An RQ value of 1
indicates that the
organisms are
using carbohydrate as the respiratory
substrate during
the course of this
experiment
WATER

14. pr2h OBTAINING RQ VALUES
WATER
During a further experiment using the respirometer, a value for
oxygen consumption of 20 mm3 in one hour was again obtained
when KOH was present in the apparatus
In this example,
the oxygen
consumed does
not equal the
amount of carbon
dioxide produced
When the KOH was replaced with water the following result
was obtained after one hour
The manometer fluid had moved upwards towards the left hand
tube by a distance of 10 mm in one hour
The carbon
dioxide is not
being absorbed
and so this result
shows that oxygen
consumption
exceeds carbon
dioxide production
by a volume of
7.86 mm3 h-1
pr2h
Using the formula
this represents
a volume of
7.86 mm3 h-1
(capillary diameter
is 1 mm)
distance
moved by
the fluid =
10 mm
As the oxygen
consumption is
known to be 20
mm3 h-1, then
carbon dioxide
production must
be mm3 h-1

15. pr2h OBTAINING RQ VALUES 12.14 mm3 h-1 RQ = = 0.61 20 mm3 h-1
An RQ value
of 0.61 suggests
that the
organisms are
using fatty acids
as the substrate
for respiration
(expected value
for fatty acids is 0.7)
WATER
OXYGEN CONSUMPTION = 20 mm3 h-1
CARBON DIOXIDE PRODUCTION = mm3 h-1 (20 – 7.86)
RQ =
12.14 mm3 h-1
20 mm3 h-1
= 0.61
The deviation of
the obtained value
from 0.7 is most
likely to be due
sources of error
in the procedure
pr2h
Using the formula
this represents
a volume of
7.86 mm3 h-1
(capillary diameter
is 1 mm)
distance
moved by
the fluid =
10 mm
Errors can arise
from leaking
joints, failure of
KOH to absorb
all the CO2 and
inaccuracy in
reading the scale

16. pr2h OBTAINING RQ VALUES
WATER
During a further experiment using the respirometer, a value for
oxygen consumption of 20 mm3 in one hour was again obtained
when KOH was present in the apparatus
In this example,
the oxygen
consumed does
not equal the
amount of carbon
dioxide produced
When the KOH was replaced with water the following result
was obtained after one hour
The manometer fluid had moved upwards towards the right hand
tube by a distance of 4 mm in one hour
The carbon
dioxide is not
being absorbed
and so this result
shows that
carbon dioxide production
exceeds oxygen
consumption
by a volume of
3.14 mm3 h-1
pr2h
Using the formula
this represents
a volume of
3.14 mm3 h-1
(capillary diameter
is 1 mm)
distance
moved by
the fluid =
4 mm
As the oxygen
consumption is
known to be 20
mm3 h-1, then
carbon dioxide
production must
be mm3 h-1

17. pr2h OBTAINING RQ VALUES 23.14 mm3 h-1 RQ = = 1.16 20 mm3 h-1
An RQ value
of 1.16 suggests
that the
organisms have
resorted to
anaerobic
respiration at
some stage during the period of the investigation
(RQ values above one suggest that some
respiration has
occurred)
OXYGEN CONSUMPTION = 20 mm3 h-1
CARBON DIOXIDE PRODUCTION = mm3 h-1 ( )
RQ =
23.14 mm3 h-1
20 mm3 h-1
= 1.16
pr2h
Using the formula
this represents
a volume of
3.14 mm3 h-1
(capillary diameter
is 1 mm)
distance
moved by
the fluid =
4 mm
WATER

18. 2. Why is RQ different for different substances 3 marks
Questions on RQ
1. What is RQ marks
2. Why is RQ different for different substances
3 marks
3. What is a respirometer 4 marks
4. What are the differences between the experimental respirometer used in class and the one in the book marks