Chapter 4 (respiration) exam questions

Question 1

Describe how ATP is made in mitochondria (6)

Answer 1

1. Substrate level
phosphorylation / ATP
produced in Krebs cycle;
2. Krebs cycle/link reaction
produces reduced
coenzyme/reduced
NAD/reduced FAD;
3. Electrons released from
reduced /coenzymes/
NAD/FAD;
4. (Electrons) pass along
carriers/through electron
transport chain/through series
of redox reactions;
5. Energy released;
6. ADP/ADP + Pi;
7. Protons move into
intermembrane space;
8. ATP synthase;

Question 2

A student investigated the rate of anaerobic respiration in yeast. She put 5 g of yeast
into a glucose solution and placed this mixture in the apparatus shown in Figure 4.
She then recorded the total volume of gas collected every 10 minutes for 1 hour.

Yeast can also respire aerobically. The student repeated the investigation with a
fresh sample of yeast in glucose solution, but without the oil. All other conditions
remained the same.
Explain what would happen to the volume of gas in the syringe if the yeast were only
respiring aerobically (2)

Respiration produces more ATP per molecule of glucose in the presence of oxygen
than it does when oxygen is absent. Explain why. (2)

Answer 2

1. (Stays the) same/level/(relatively) constant;
2. Same volume/amount of oxygen uptake and
   carbon dioxide release;
3. Oxygen is final/terminal (electron) acceptor /
   oxygen combines with electrons and protons;
4. Oxidative phosphorylation / electron transport
   chain provides ATP;
5. Only glycolysis occurs without oxygen / no Krebs
   / no link reaction;

Question 3

Describe how acetylcoenzyme A is formed in the link reaction (2)

Answer 3

1. Oxidation of/hydrogen removed from
   pyruvate and carbon dioxide
   released;
2. Addition of coenzyme A;

Question 4

In the Krebs cycle, acetylcoenzyme A combines with four-carbon oxaloacetate to form
six-carbon citrate. This reaction is catalysed by the enzyme citrate synthase.

Oxaloacetate is the first substrate to bind with the enzyme citrate synthase. This
induces a change in the enzyme, which enables the acetylcoenzyme A to bind.
Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the enzyme (2)

Another substance in the Krebs cycle is called succinyl coenzyme A. This substance
has a very similar shape to acetylcoenzyme A.
Suggest how production of succinyl coenzyme A could control the rate of the reaction
catalysed by citrate synthase. (2)

Answer 4

1. Change (in shape) of active site /
active site moulds around the
substrate;
2. (Substrate/active site) now
complementary;

1. Is a competitive inhibitor / attaches
   to active site;
2. Reduces/prevents enzymesubstrate/E-S
   complex forming;

Question 5

In muscles, pyruvate is converted to lactate during anaerobic respiration.
Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration (2)

In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this. (1)

Answer 5

1. Regenerates/produces NAD /
   oxidises reduced NAD;
2. (NAD used) in glycolysis;
   Accept description of glycolysis

(Pyruvate used) in aerobic respiration /
(lactate/lactic acid) is
toxic/harmful/causes cramp/(muscle)
fatigue;

Question 6

A scientist investigated the effect of the enzyme inhibitor malonate on this reaction.
The structure of malonate is very similar to the structure of succinate. The scientist added malonate and the respiratory substrate, pyruvate, to a suspension of isolated
mitochondria. She also bubbled oxygen through the suspension.

Explain why the scientist did not use glucose as the respiratory substrate for these
isolated mitochondria. (2)

Explain how malonate inhibits the formation of fumarate from succinate. (2)

Answer 6

1. Glucose is used/broken down
during glycolysis/in cytoplasm;
2. Glucose cannot cross
mitochondrial membrane(s) /
pyruvate can cross mitochondrial
membrane(s);

1. Is a competitive inhibitor /
   attaches to active site;
2. Reduces/prevents enzyme substrate/E-S
   complex forming;

Question 7

For Glycolysis, Link and Krebs state true or false:

Occurs in mitochondria?
CO2 produced?
NAD reduced?
3

Answer 7

G = fft
L = ttt
K = ttt

Question 8

Suggest why the rate of gas production decreased between 50 and 60 minutes. (1)

Answer 8

Glucose decreases/is a limiting factor / increase in

ethanol / yeast/cells die / toxins build up;

Question 9

The anaerobic digester has a cooling system, which is not shown in the diagram.
Without this cooling system the digester would soon stop working. Explain why. (2)

Answer 9

1. Respiration causes temperature increase/release of heat;

2. Enzymes would be denatured/microorganisms killed;