Sample exam questions:
Use lined paper for these questions. Remember – layout out your ideas clearly.
34. Describe the role of Acetyl CoA in the metabolism of lipids. (2 marks)
Lipids may enter the respiration pathway as fatty acids, hydrolyzed to 2 carbon
compounds, (acetate) which are modified by addition of CoA cofactor, making
acetyl CoA. Fatty acids with even numbers of carbon result in no additional
release of carbon dioxide, those with odd number of carbon release an extra
CO2 molecule.
35. Explain chemiosmosis as it occurs in respiration. (2 marks)
Chemiosmosis refers to the process by which protons, having been released
from NADH/H+ and FADH2, are transported to and concentrated in the intermembrane space in the mitochondrion. The protons move down a
concentration gradient, through the inner membrane, to the matrix, while the
energy released in this process is coupled to the phosphorylation of ADP to ATP.
36. Explain the process of aerobic respiration, including oxidative phosphorylation
(8 marks)
Points to include:

Initial role for link reaction, in the matrix, pyruvate conversion to
acetate, with the release of CO2, and production of NADH

2 turns of the Kreb’s Cycle for each pyruvate, each resulting in the
oxidation of acetyl CoA to 2 CO2 molecules, production of 3
NADH, 1ATP (substrate level phosphorylation) and 1FADH2

Kreb’s Cycle takes place using soluble enzymes in the matrix of
the mitochondrion

The reduced products (NADH, FADH2) of the KC serve as
substrate/donors for the ETC

Protons are shunted across the inner membrane and
concentrated in the IMS

Electrons are transferred through the inner membrane via
carriers

Final electron acceptor is oxygen, combining with protons to
make water

Protons are released through the ATP synthase as described in
the previous question.
37. Compare aerobic and anaerobic respiration, including yield of ATP. (6 marks)
 Aerobic results in a large yields of ATP, anaerobic, small
 Aerobic requires the presence of oxygen, anaerobic does not
 Aerobic occurs within the mitochondria, anaerobic in the cytoplasm
 Aerobic is consistent in various organisms, anaerobic takes produces
different products in yeast and mammals
 Both oxidize carbon compounds to reduced organic molecules
 Aerobic is effective for ongoing energy production, anaerobic for short
term needs
Sample data analysis question (from IB QuestionBank)
38. At the start of glycolysis, glucose is phosphorylated to produce glucose 6phosphate, which is converted into fructose 6-phosphate. A second
phosphorylation reaction is then carried out, in which fructose 6-phosphate is
converted into fructose
1,6-bisphosphate. This reaction is
catalyzed by the enzyme phosphofructokinase.
Biochemists measured the enzyme activity of phosphofructokinase (the rate at
which it catalyzed the reaction) at different concentrations of fructose 6phosphate. The enzyme activity was measured with a low concentration of ATP and
a high concentration of ATP in the reaction mixture. The graph below shows the
results.
Low ATP concentration
Enzyme activity
High ATP concentration
Fructose 6-phosphate concentration
(a)
(i)
Using only the data in the above graph, outline the effect of increasing
fructose 6-phosphate concentration on the activity of
phosphofructokinase, at a low ATP concentration.
As F6P concentration increases, PFKase activity increases, rapidly at
first and then plateaus
(2)
(ii)
Explain how increases in fructose 6-phosphate concentration affect the
activity of the enzyme.
As concentration of F6P increases, more substrate molecules are in
close proximity to the enzyme active site, thus increasing the likelihood
of reaction occurring.
(2)
(b)
(i)
Outline the effect of increasing the ATP concentration on the activity
of phosphofructokinase.
PFKase enzyme requires ATP to function, the more ATP available, the
more access the enzyme has to the essential energy source.
(2)
(ii)
Suggest an advantage to living organisms of the effect of ATP on
phosphofructokinase.
Living organisms will be actively respiring and will have access to a
direct source of ATP to empower enzymes. If there is already a rich
source of ATP, then it is wasteful to continue the process that makes
even more. SO having the rate of respiration dependent upon ATP
concentration is a valuable regulation.
(1)
(Total 7 marks)