12.10 End of Chapter Questions

Posted14/12/2024

Updated14/12/2024

ByBMF

Click on each box or question to see the answers.

Question 1 – 3:

1. What does not occur in the conversion of glucose to two molecules of pyruvate? [1]
A hydrolysis of ATP
B phosphorylation of ATP
C phosphorylation of triose (3C) sugar
D reduction of NAD

2. Where does each stage of aerobic respiration occur in a eukaryotic cell? [1]

	Link reaction:	Krebs cycle:	Oxidative phosphorylation:
A	cytoplasm	mitochondrial matrix	mitochondrial cristae
B	mitochondrial cristae	cytoplasm	mitochondrial matrix
C	cytoplasm	mitochondrial cristae	mitochondrial matrix
D	mitochondrial matrix	mitochondrial matrix	mitochondrial cristae

3. The diagram summarises how glucose can be used to produce ATP, without the use of oxygen.

Which compounds are represented by the letters X, Y and Z ?

	X	Y	Z
A	ethanol	pyruvate	lactate
B	lactate	ethanol	pyruvate
C	pyruvate	ethanol	lactate
D	pyruvate	lactate	ethanol

Question 4:

Distinguish between:
a) an energy currency molecule and an energy storage molecule [2]

energy currency:
immediate donor of energy to all energy requiring reactions in a cell;
energy storage:
short-term (glucose, sucrose) or long-term
(starch, glycogen, triglyceride) store of
chemical potential energy;

b) decarboxylation and dehydrogenation. [2]

decarboxylation:
a reaction in which carbon dioxide is
removed from a compound; [1]
dehydrogenation:
a reaction in which hydrogen is removed
from a compound; [1]

Question 5:

State the roles in respiration of:
a) NAD [1]

NAD:
a hydrogen carrier molecule: it accepts a
hydrogen from one reaction and donates it to
another;

b) coenzyme A [1]

coenzyme A:
a carrier of an acetyl group from the link
reaction to the Krebs cycle;

c) oxygen. [1]

oxygen:
the final electron acceptor and hydrogen ion
acceptor in oxidative phosphorylation: the
oxygen is reduced to water;

Question 6:

Copy and complete the table to show how much ATP is used and produced for each molecule of glucose respired in the
various stages of respiration. [5]

	ATP used:	ATP produced:	Net gain in ATP:
glycolysis
link reaction
Krebs cycle
oxidative phosphorylation
Total

Feature:	ATP used:	ATP produced:	Net gain in ATP:
glycolysis	–2	+4	+2
link reaction	0	0	0
Krebs cycle	0	+2	+2
oxidative phosphorylation	0	+28	+28
total	–2	+34	+32

Question 7:

a) Explain why the energy value of lipid is more than twice that of carbohydrate. [2]

Lipid has more hydrogen atoms per molecule than does carbohydrate;
most energy liberated in aerobic respiration comes from the oxidation of hydrogen to water;

b) Explain what is meant by respiratory quotient (RQ). [2]

c) Copy and complete the table to show the respiratory substrates with each of the given RQs. [3]

Respiratory substrate:	RQ:
1.0
0.7
0.9

Respiratory substrate:	RQ:
carbohydrate	1.0
lipid	0.7
protein	0.9

d) Measurements of oxygen uptake and carbon dioxide production by germinating seeds in a respirometer showed that 25 cm³ of oxygen was used and 17.5 cm³ of carbon dioxide was produced over the same time period.
i. Calculate the RQ for these seeds. [2]

ii. Identify the respiratory substrate used by the seeds. [1]

lipid;

e) Dahlia plants store a compound called inulin, which is a polymer of fructose. The structure of fructose is shown in the diagram.

Calculate the RQ when inulin is hydrolysed and then respired aerobically. [2]

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy;

Question 8:

Copy and complete the following passage describing the adaptations of rice for growing with its roots submerged in water.
The stems and leaves of rice plants have very large …………. in tissue called …………., which allow oxygen to pass from the air to the …………. . The roots are very shallow, giving them access to the higher concentration of …………. in surface water. When oxygen concentrations fall, the roots can oxidise glucose through …………. …………. .
This produces …………., which is toxic. However, the root cells are tolerant of higher concentrations of this than are most cells and they also contain high concentrations of the enzyme …………. to break it down. [7]

1 air spaces;
2 aerenchyma;
3 roots;
4 oxygen;
5 anaerobic pathways;
6 ethanol / alcohol;
7 alcohol dehydrogenase;

Question 9:

In aerobic respiration, the Krebs cycle is regarded as a series of small steps. One of these steps is the conversion of succinate to fumarate by an enzyme, succinate dehydrogenase.

a) State the role played by dehydrogenase enzymes in the Krebs cycle and explain briefly the importance of this role in the production of ATP. [3]

provide hydrogen to reduce NAD and FAD;
reduced carriers pass to electron transport chain;
provide energy for ATP synthesis in oxidative phosphorylation;
refer to chemiosmosis;

b) An investigation was carried out into the effect of different concentrations of aluminium ions on the activity of succinate dehydrogenase. The enzyme concentration and all other conditions were kept constant. The graph below shows the results of this investigation.

With reference to the graph:
i. describe the effect of the concentration of aluminium ions on the rate of production of fumarate [2]

increasing the concentration of aluminium ions from 0 to 40 µmol increases rate of fumarate production;
increases from 40 to 120 µmol have little effect;

ii. suggest an explanation for this effect. [2]

aluminium binds to enzyme / refer to cofactor;

optimises shape of active site;

Question 10:

ATP is sometimes described as ‘the universal energy currency’. Describe the features of ATP that make it suitable as an energy source in cells. [3]

ATP provides an immediate source of energy for energy-consuming processes in cells.
A molecule of ATP consists of adenine and ribose, forming adenosine, which in turn is joined covalently to three phosphate groups.
The hydrolysis of ATP to ADP (adenosine diphosphate) yields 30.5 kJ per mole of free energy, providing energy for processes such as protein synthesis and active transport.
ATP is also used in phosphorylation reactions, in which the third phosphate group is transferred to another molecule, known as a phosphoryl transfer reaction. An example of this reaction is found in the formation of glucose 6-phosphate at the start of glycolysis.

Question 11:

In aerobic respiration, ATP is synthesised directly in glycolysis and in the Krebs cycle. This is referred to as ‘substrate level phosphorylation’. Find out which reactions of glycolysis involve substrate level phosphorylation. [2]

Two reactions in glycolysis result in the phosphorylation of ADP to form ATP:
- conversion of 1,3-bisphosphoglycerate to 3-phosphoglyceraldehyde
- conversion of phosphoenolpyruvate to pyruvate.

Question 12:

State where each of the following stages of aerobic respiration occur in a eukaryotic cell:

a) glycolysis [1]

Glycolysis occurs in the cytoplasm.

b) the link reaction [1]

The link reaction occurs in the mitochondrial matrix.

c) the Krebs cycle [1]

The Krebs cycle occurs in the mitochondrial matrix.

d) oxidative phosphorylation [1]

Oxidative phosphorylation occurs across the inner mitochondrial membrane. [1]

Question 13:

Outline the role of the coenzyme NAD in respiration. [4]

NAD is an example of an electron carrier in the oxidation of molecules in the process of respiration.
In aerobic respiration, the final electron acceptor is oxygen.
As molecules are oxidised in respiration, the electrons are transferred to special carriers, which then transfer electrons to oxygen during the process of oxidative phosphorylation, in the electron transport chain (ETC).
Oxidation of a substrate in respiration involves the removal of two hydrogen atoms. One of these is transferred to NAD, the other forms H⁺ and an electron. The electron is carried by NAD.

Overall, this reaction can be summarised as:

substrate – H₂ + NAD⁺ substrate + NADH + H⁺

Note that in the oxidised state, NAD is NAD⁺ and when reduced, it forms NADH + H⁺. [4]

Question 14:

The complete oxidation of one type of fatty acid molecule yields 129 molecules of ATP. Compare this yield of ATP with the yield of ATP from the oxidation of a carbohydrate molecule and suggest an explanation for the difference. [3]

The yield of ATP from the oxidation of the fatty acid is much higher than it is from the oxidation of a carbohydrate (over 3 times higher).
This is because the complete oxidation of a fatty acid yields larger numbers of reduced electron carriers, NAD and FAD, than the oxidation of a carbohydrate.
This results in the production of more ATP in oxidative phosphorylation.

Question 15:

Define the term respiratory quotient (RQ). [2]

RQ is defined as the volume of carbon dioxide produced in respiration divided by the volume of oxygen used. RQ has no units.

Calculate the respiratory quotient for the complete oxidation of a fatty acid with the formula CH₃(CH₂)₁₄COOH. [3]
[Hint: you need to write a balanced equation to show the complete oxidation of this fatty acid] [3]

Writing a balanced equation for the complete oxidation of this fatty acid shows that 23 molecules of oxygen are used and 16 molecules of carbon dioxide are produced.
Therefore, the RQ value is 16 ÷ 23 = 0.696 (0.7 to one decimal place).

BioMed Foundation

12. Energy and respiration

12.10 End of Chapter Questions