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7 (a) Fig. 7.1 is a diagram of a section through a mitochondrion.

circular
P
42
DNA

Q
S R

Fig. 7.1

(i) Using Fig. 7.1, state the letter which indicates the site of:

• the Krebs cycle ........................

• oxidative phosphorylation ........................

• decarboxylation. ........................
[3]

(ii) Suggest one function for the circular DNA in Fig. 7.1.

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(b) During respiration, exchange of substances takes place between the cytoplasm and the
mitochondria.

Complete the table below to list three substances that enter the mitochondria and three
substances that leave the mitochondria.

substance that enters substance that leaves

the mitochondria the mitochondria

[3]

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(c) The poison cyanide binds with cytochrome oxidase, one of the carriers in the electron
transport system.

Suggest how ingestion of cyanide by humans leads to death by muscle failure.

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(d) Tripalmitin is a triglyceride. The chemical equation for the aerobic respiration of tripalmitin is:

2C51H98O6 + 145O2 102CO2 + 98H2O

(i) Calculate the RQ value for tripalmitin.

Give your answer to 2 decimal places.

Show your working.

answer ...............................................................
[2]

(ii) Explain why the usual RQ value for respiration in humans is between 0.7 and 1.0.

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[Total: 15]
© UCLES 2016 9700/42/F/M/16 [Turn over
 4

2 (a) During a sporting event, an athlete carries out respiration in aerobic conditions.

(i) Complete Table 2.1 to state the precise locations within a muscle cell of glycolysis, the
link reaction, the Krebs cycle and oxidative phosphorylation.

Table 2.1

process precise location

glycolysis

link reaction

Krebs cycle

oxidative phosphorylation

[2]

(ii) In a muscle cell, molecules of glucose are phosphorylated at the start of glycolysis.

Suggest why the phosphorylated glucose molecules cannot diffuse out of the cell.

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© UCLES 2017 9700/42/F/M/17

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(b) Sometimes an athlete will need to carry out respiration in anaerobic conditions to produce ATP.

Explain why the respiration of glucose in anaerobic conditions produces less ATP than in
aerobic conditions.

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(c) For a short time after exercise, a person continues to breathe more heavily than at rest to
take in more oxygen than normal.

Explain the use of this extra oxygen.

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[Total: 12]

© UCLES 2017 9700/42/F/M/17 [Turn over

 24

8 Structures and compounds involved in respiration include:

1 coenzyme A

2 cytoplasm

3 pyruvate

4 NAD

5 outer mitochondrial membrane

6 carrier protein

7 inner mitochondrial membrane

8 intermembrane space of mitochondrion

9 ADP

10 acetyl group

Match each of the descriptions with one number chosen from 1 to 10, to show the correct structure
or compound.

You may use each number once, more than once or not at all.

location of ATP synthase ....................

transports hydrogen atoms ....................

nucleotide with a purine base ....................

location of substrate-linked phosphorylation ....................

enters the Krebs cycle ....................

produced by oxidation of triose phosphate ....................

[6]

[Total: 6]

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7 (a) Isolated mitochondria were used to investigate respiration.

• Mitochondria were extracted from respiring mammalian cells and incubated in a

buffer solution.
• Pyruvate and inorganic phosphate (Pi) were added at time zero.
• ADP was added one minute later.
• The oxygen concentration of the buffer solution containing mitochondria was
monitored throughout the investigation.

The results of the investigation are shown in Fig. 7.1.

phase A

phase B
oxygen
concentration of
buffer solution
containing
mitochondria

phase C

0 1 2 3 4 5
time / min

pyruvate ADP
and Pi added
added

Fig. 7.1

(i) Suggest why the line of the graph in Fig. 7.1 is steeper during phase B than during
phase A.

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(ii) Suggest why the line of the graph starts to level out in phase C.

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© UCLES 2019 9700/42/F/M/19
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(b) Some plants, such as rice, grow with their roots submerged in water.

Fig. 7.2 shows a group of rice plants.

Fig. 7.2

Explain how rice is adapted to grow with its roots submerged in water.

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[Total: 9]

© UCLES 2019 9700/42/F/M/19 [Turn over