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CAIE A-Level Biology A2 12.2 Respiration Questions

Practise how carbon, coenzymes and ATP move through aerobic respiration, compare fermentation and investigate respiration using indicators or a respirometer.

Syllabus
2028–2030
Course
Biology 9700
Level
A2

Exam points

  • Locate glycolysis, link reaction, Krebs cycle and oxidative phosphorylation within the cell.
  • Trace glycolysis from glucose phosphorylation and six-carbon splitting to pyruvate, ATP and reduced NAD.
  • Explain pyruvate entry and link-reaction decarboxylation, dehydrogenation and acetyl-CoA formation.
  • Trace acetyl-CoA carbon through citrate formation, Krebs-cycle decarboxylation and oxaloacetate regeneration.
  • Explain NAD and FAD reduction in respiration and hydrogen transfer to carriers in the inner mitochondrial membrane.
  • Explain electron transport, proton pumping, ATP synthase chemiosmosis and oxygen's role as final acceptor.
  • Predict how ETC inhibition or proton-gradient loss affects oxidative phosphorylation and ATP production.
  • Relate inner-membrane cristae surface area to respiratory protein capacity and aerobic ATP production.
  • Compare lactate and ethanol fermentation with aerobic respiration, including NAD regeneration and lower ATP yield.
  • Explain how rice aerenchyma, ethanol tolerance and stem elongation aid survival during flooding.
  • Plan yeast-respiration tests using DCPIP or methylene blue to compare substrate concentration or temperature.
  • Use a respirometer to test temperature effects on oxygen uptake with controls, repeats and rate calculations.

Covered syllabus points

12.2.1—Four stages of aerobic respiration location12.2.2—Glycolysis pathway12.2.3—Pyruvate and the link reaction12.2.4—Link reaction12.2.5—Krebs cycle carbon compounds12.2.6—Krebs cycle redox reactions12.2.7—NAD and FAD in respiration12.2.8—Oxidative phosphorylation12.2.9—Mitochondria structure-function relationship12.2.10—Lactate and ethanol fermentation12.2.11—Energy yield12.2.12—Rice adaptations to flooding12.2.13—Redox indicator investigation12.2.14—Respirometer investigations

Question 1

[Maximum number: 10]

Oxygen is needed for aerobic respiration in cells.
In eukaryotic cells, the mitochondrion is the organelle used for aerobic respiration.

Question (a)

(a)

Fig. 1.1 shows a transmission electron micrograph of a mitochondrion.

Fig. 1.1

Fig. 1.1

Table 1.1 lists the four stages of aerobic respiration.
With reference to Fig. 1.1, complete Table 1.1 using the letters A-D to show where each stage occurs.

Each letter may be used once, more than once or not at all.

Table 1.1

Table 1.1

[ 3 ]

Question (b)

(b)

In anaerobic conditions, no ATP can be synthesised by oxidative phosphorylation because the process stops.

Explain why ATP synthesis by oxidative phosphorylation stops in anaerobic conditions.

[ 4 ]

Question (c)

(c)

Up to 60% of the ATP that is produced in cancer cells comes from lactate fermentation of glucose, even though oxygen is present.

Scientists are developing cancer treatments to inhibit the enzyme that catalyses the last step of lactate fermentation.

Explain how the inhibition of this enzyme reduces the production of ATP in cancer cells.

[ 3 ]

Question 2

[Maximum number: 8]

Question (a)

(a)

Glycolysis is a biochemical pathway that occurs in the cytoplasm of cells.
In glycolysis, a molecule of glucose is metabolised to two molecules of pyruvate. The process is outlined in Fig. 1.1.

Fig. 1.1

Fig. 1.1

[ 2 ]

Question (i)

(i)

Explain why glucose is phosphorylated at the beginning of glycolysis.

[ 1 ]

Question (ii)

(ii)

Suggest one use of the reduced NAD that is produced in glycolysis.

[ 1 ]

Question (b)

(b)

Pyruvate can enter the mitochondrion by active transport.

Describe the main conditions that are required for pyruvate to enter the mitochondrion by active transport.

[ 3 ]

Question (c)

(c)

Pyruvate is involved in the link reaction in the matrix of the mitochondrion.

Describe the link reaction.

[ 3 ]

Question 3

[Maximum number: 15]

Question (a)

(a)

Outline the process of glycolysis.

[ 6 ]

Question (b)

(b)

Describe the series of reactions that make up the Krebs cycle.

[ 9 ]

Question 4

[Maximum number: 3]

Oxygen is needed for aerobic respiration in cells.
In eukaryotic cells, the mitochondrion is the organelle used for aerobic respiration.

Fig. 1.1 shows a transmission electron micrograph of a mitochondrion.

Fig. 1.1

Fig. 1.1

Table 1.1 lists the four stages of aerobic respiration.
With reference to Fig. 1.1, complete Table 1.1 using the letters A-D to show where each stage occurs.

Each letter may be used once, more than once or not at all.

Table 1.1

Table 1.1

Question 5

[Maximum number: 1]

Glycolysis is a biochemical pathway that occurs in the cytoplasm of cells.
In glycolysis, a molecule of glucose is metabolised to two molecules of pyruvate. The process is outlined in Fig. 1.1.

Fig. 1.1

Fig. 1.1

Explain why glucose is phosphorylated at the beginning of glycolysis.

Question 6

[Maximum number: 3]

Pyruvate can enter the mitochondrion by active transport.

Describe the main conditions that are required for pyruvate to enter the mitochondrion by active transport.

Question 7

[Maximum number: 3]

Pyruvate is involved in the link reaction in the matrix of the mitochondrion.

Describe the link reaction.

Question 8

[Maximum number: 9]

Describe the series of reactions that make up the Krebs cycle.

Question 9

[Maximum number: 2]

At the end of glycolysis in mammalian muscle tissue, pyruvate is formed. Pyruvate can be further metabolised along two different pathways, pathway 1 and pathway 2 .

Fig. 6.1 outlines the two pathways.

Fig. 6.1

Fig. 6.1

Name the two types of reaction that are involved in pathway 1.

Question 10

[Maximum number: 5]

Many factors affect the rate of cellular respiration.

Coenzymes are important in aerobic respiration.

Outline the roles of named coenzymes in aerobic respiration.

Question 11

[Maximum number: 7]

Identify protein D and the group of proteins represented by A, B and C and describe their roles in oxidative phosphorylation.

Question 12

[Maximum number: 4]

Question (a)

(a)

Fig. 6.1 is a diagram of part of a mitochondrion.

Fig. 6.1

Fig. 6.1

On Fig. 6.1, use arrows to show the route taken by oxygen from the cytoplasm into the mitochondrial matrix.

[ 1 ]

Question (b)

(b)

The matrix of a mitochondrion contains small circular DNA. In the cells of humans, the mitochondria have circular DNA that contains 37 genes.

Suggest functions for these mitochondrial genes.

[ 3 ]

Question 13

[Maximum number: 3]

Oxygen is needed for aerobic respiration in cells.
In eukaryotic cells, the mitochondrion is the organelle used for aerobic respiration.

Up to 60% of the ATP that is produced in cancer cells comes from lactate fermentation of glucose, even though oxygen is present.

Scientists are developing cancer treatments to inhibit the enzyme that catalyses the last step of lactate fermentation.

Explain how the inhibition of this enzyme reduces the production of ATP in cancer cells.

Question 14

[Maximum number: 5]

Sometimes the muscle cells of an athlete need to carry out respiration in anaerobic conditions.

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

Question 15

[Maximum number: 3]

The cereal crop rice, Oryza sativa, grows in fields that are flooded with water. The roots of the rice plants are submerged in water that contains very little oxygen.

Describe and explain how rice plants are adapted to grow in flooded fields.

Question 16

[Maximum number: 8]

Describe how you would carry out an investigation to calculate the effect of substrate concentration on the rate of respiration of yeast in anaerobic conditions using a redox indicator, such as DCPIP or methylene blue.

Question 17

[Maximum number: 7]

Describe how you would carry out an investigation, using a simple respirometer, to measure the effect of temperature on the respiration rate of insect larvae.

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