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Module 5
Respiration
5.2.2 j,k. RESPIRATORY SUBSTRATE
Learning Outcomes
 Define
the term respiratory substrate
 Calculate
 Explain
rates of respiration
the difference in relative energy
values of carbohydrate, lipid and
protein respiratory substrates
Starter – Anaerobic recap
Yeast
Hydrogen acceptor
ethanol
Mammals
Pyruvate
Is carbon dioxide
produced?
Yes
No
Is ATP produced?
No
No
Is NAD reoxidised?
Yes
Yes
End products
Enzymes involved
Ethanol and Carbon
dioxide
Pyruvate decarboxylase,
ethanol dehydrogenase
Lactate
Lactate
dehydrogenase
1. Explain how a build up of acid during glycolysis leads to muscle fatigue
in mammals.
2. Suggest how diving mammals, such as seals, whales and dolphins can
swim below water without suffering from muscle fatigue.
Respiratory substrate

Write down a definition of respiratory substrate.

Any biological molecule that can be broken down
in respiration to release energy is called a respiratory
substrate. Cells respire glucose, but also respire other
carbohydrates, lipids and proteins, but these enter
respiration at different points.
Energy values of different respiratory
substrates

Where is most ATP made during respiration?

Oxidative phosphorylation, when H ions (protons) flow through
channels. The H ions and electrons then combine with oxygen to
produce water. The more protons, the more ATP.

Which respiratory substrate would produce the most energy content?

The more H atoms in a molecule of respiratory substrate, the more
ATP is generated when that substrate is respired. So the more H
atoms per mole of respiratory substrate, then more oxygen is needed
to respire that substance.

(One mole is the gram molecular mass of a
substance. 180g glucose is one mole of glucose)
Respiratory substrates
Other substances as well as glucose can be respired. Different
respiratory substrates release different amounts of energy.
Respiratory substrate
Mean energy value (kJ g-1)
carbohydrate
15.8
lipid
39.4
protein
17.0
The difference in the relative energy values of these respiratory
substrates is due to the amount of hydrogen atoms present in
each one. If more hydrogen atoms are available to reduce
coenzymes, more energy can subsequently be generated in
the electron transport chain.
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Energy values of different respiratory
substrates

Produce 3 flow diagrams explaining how carbohydrate, lipid and
protein produce energy – Using page 96-97

Complete stretch and challenge question
Respiratory rate
The respiratory rate is the
rate at which an organism
converts glucose to CO2 and
water. It can be calculated by
measuring an organism’s rate
of oxygen consumption.
Studies on simple animals
often use a respirometer.
Respirometers measure the change in gas volume in a
closed system. Any change is due to the respiratory activity of
the study organisms. Potassium hydroxide or soda lime is
used to absorb the carbon dioxide produced, meaning any
changes in volume are due to oxygen consumption.
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Respirometer experiments
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Respiratory quotient
Respiratory quotient (RQ) is the volume of carbon dioxide
produced when the respiratory substrate is respired, dividing
by the volume of oxygen consumed, in a set period of time.
RQ =
volume of CO2 given out
volume of O2 taken in
RQ gives an indication of the respiratory substrate being
respired and whether respiration is aerobic or anaerobic.
Type of respiration
Substrate
RQ
anaerobic
glucose
aerobic
carbohydrate
>1
1.0
protein
approx. 0.9
lipid
approx. 0.7
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Measuring Respiration
• The equation for respiration using oleic
acid is below. Calculate the RQ.
2C18H34O2 + 51O2
 36CO2
+ 34H2O + energy
• What type of molecule is oleic acid?
• Is it aerobic or anaerobic respiration?
RQ = 36/51 = 0.71
Oleic acid is a fatty acid. Fatty acids make
up triglycerides. Its aerobic respiration.
• Complete workbook question page 98
OCR A2 – complete for homework
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