The respiratory substrates that can be used include glucose, lipids like fatty acids, and amino acids. Fatty acids are broken down into acetyl-CoA which enters the Krebs cycle, and the more hydrogens present the more ATP can be produced. Glycerol from lipids can also be used to produce ATP. Proteins are broken down into amino acids and then into acetyl-CoA or pyruvate. The energy value of substrates is measured using a calorimeter and varies with carbohydrates having the lowest at 15.8 KJg-1 and lipids the highest at 39.4 KJg-1. The respiratory quotient is used to determine the substrate being used based on the ratio of CO2 produced

1. Respiratory
Substrates

2. Respiratory substrates
The usual respiratory substrate is glucose
Some cells can only respire glucose, such as
brain neurones
Other cells can oxidize lipids or amino acids

3. Lipids
These are broken down to fatty acids and glycerol
Fatty acids
are then broken into pairs of Carbon atoms
As Acetyl CoA
which enters the Krebs cycle

4. Fatty acids
These are then broken
into pairs of Carbon
atoms
As Acetyl CoA
which enters the Krebs
cycle
The more hydrogens the
more NAD reduced can
be made
This will form ATP in
oxidative
phosphorylation

5. One molecule of stearic acid
will yield 147 ATP

6. Most of the energy from respiration is
from oxidation of hydrogen to water
The more hydrogens there are, the
more energy can be released
Fatty-acids therefore have a high
energy value per unit mass

7. Glycerol
can be phosphorylated to and finally incorporated into
glycolysis
One molecule of glycerol will yield 19ATP

8. Proteins
These are hydrolysed
to amino-acids
These are deaminated
to remove the amino
group or transaminated
to transfer the amino
group to another
molecule

9. The hydrocarbon
skeleton is then
converted to
pyruvate or
Acetyl CoA
which will enter
the Krebs cycle

10. Energy Values of
Substrates
These are found using a CALORIMETER
A known mass of the substrate is burnt completely
in the presence of oxygen
The energy given off as heat is used to raise the
temperature of a known volume of water

12. The energy value per unit mass of the
substrate can be found using the Specific
Heat Capacity of water
The energy values of Substrates are:
Carbohydrates – 15.8 KJg-1
Lipids – 39.4 KJg-1
Protein – 17.0 KJg-1

13. Respiratory Quotients (RQ)
These are used to determine the respiratiry
substrate being used in resiration
For Carbohydrates:
C6H12O6 + 602 6CO2 + 6H2O +
ENERGY
02 IN : CO2 OUT
1 : 1

14. RQ = Volume of CO2 OUT per
unit time
Volume of 02 IN per unit
time
Or RQ = moles of CO2 out
moles of 02 in

15. For example
the RQ of glucose = 6/6 = 1.0
Oleic acid:
C18H34O2 + 25.502 18CO2 +
17H2O + ENERGY
RQ = moles of CO2 out
moles of 02 in
=18/25.5
= 0.7

16. RQ
carbohydrate 1
Lipid 0.7
Protein 0.9
These are the respiratory
quotients of substrates

17. For anaerobic respiration in yeast
C6H12O6 2C2H5OH + 2CO2 + 2ATP
RQ = moles of CO2 out
moles of 02 in
= 2/0
= infinity
However because there is some aerobic respiration
so some oxygen IN the RQ will be high
less than 2
A high value for RQ will indicate some anaerobic
respiration

18. Respirometer
This is used to measure oxygen uptake
And to find RQ values or
to investigate rates of respiration
a sealed chamber and method to measure
volume changes
CO2 is absorbed by soda lime or
concentrated Potassium/ sodium hydroxide

19. Any decrease in air volume will be
because oxygen is being taken up
The amount of oxygen used per
unit time will give a rate

20. The temperature and
pressure must be kept
constant or accounted
for using a control
If investigating the
effect of a variable on
the rate of respiration:
All other factors must
be constant

21. If finding the RQ of an organism to
determine the respiratory
substrates being used:
First find the volume of oxygen used in a
specified time, e.g. xcm3
min-1

22. Remove the soda lime and repeat under
the same conditions
If carbohydrates are being respired the
plunger will not move O2 used and CO2
made will be xcm3
min-1
RQ = Volume of CO2 OUT per unit time
Volume of 02 IN per unit time
= x/x
= 1

23. If there is some anaerobic respiration
more CO2 will be made than O2 used
The plunger will move to the right
If it moves y cm3
min-1
then the total volume
of CO2 will be (x + y)cm3
min-1

24. RQ = Volume of CO2 OUT per unit time
Volume of 02 IN per unit time
= (x + y)/x

25. If fats are being respired there will be less CO2
made than O2 used because there is no glycolysis
or link reaction
The plunger will move to the left by z cm3
min-1
The amount CO2 of made is (x - z)cm3
min-1

26. RQ = Volume of CO2 OUT per unit time
Volume of 02 IN per unit time
= x - z/x