Section 3: Cellular respiration and energy in muscle

Follow where each product goes next: pyruvate, acetyl coenzyme A, citrate, NADH, then the electron transport chain and ATP synthase.

A lesson for this section

Section 1 style: multiple choice

Question 1Section 1 style

Which row describes the part played by ATP in the two phases of glycolysis?

Question 2Section 1 style

In a cell, glycolysis uses 2 molecules of ATP for each glucose molecule in the energy investment phase and generates 4 molecules of ATP in the energy pay-off stage. How many glucose molecules must pass through glycolysis to give a net gain of 36 molecules of ATP?

Question 3Section 1 style

What happens to pyruvate from glycolysis in aerobic conditions?

Question 4Section 1 style

In the citric acid cycle, which two substances combine to form citrate?

Question 5Section 1 style

Which row shows where glycolysis and the citric acid cycle take place in a cell?

Question 6Section 1 style

Three statements about dehydrogenase enzymes are given. Statement 1: they remove hydrogen ions and electrons from their substrates. Statement 2: they act only in the citric acid cycle. Statement 3: they pass hydrogen ions and electrons to the coenzyme NAD, forming NADH. Which statements are correct?

Question 7Section 1 style

Which row shows whether NADH is formed by dehydrogenase enzymes in each stage of aerobic respiration?

Question 8Section 1 style

DCPIP is a blue dye that becomes colourless when it accepts hydrogen ions and electrons removed by dehydrogenase enzymes. A muscle extract was mixed with a respiratory substrate and DCPIP. The DCPIP became colourless in 4.0 minutes at 35 °C and in 10.0 minutes at 20 °C. The rate of dehydrogenase activity is taken as 1 divided by the time. What is the rate at 20 °C as a percentage of the rate at 35 °C?

Question 9Section 1 style

Resazurin is a dye that changes from blue to pink when it accepts hydrogen ions and electrons removed by dehydrogenase enzymes. A student added resazurin to a tube of living yeast in glucose solution at 30 °C and timed the colour change. Which control would show that the colour change is caused by the yeast's enzymes?

Question 10Section 1 style

Which of these stages of cellular respiration releases carbon dioxide?

Question 11Section 1 style

As electrons are passed along the electron transport chain, energy is released. What is this energy used for?

Question 12Section 1 style

A substance makes the inner mitochondrial membrane leaky to hydrogen ions, so they flow back across it without passing through ATP synthase. Electrons still pass along the electron transport chain to oxygen. Which describes the effect on the mitochondria?

Question 13Section 1 style

Which statement about ATP synthase is correct?

Question 14Section 1 style

Luciferase is an enzyme that makes a substance called luciferin give out light when energy is supplied to the reaction. Four tubes each contained luciferin. Tube 1: luciferase and water. Tube 2: luciferase and glucose solution. Tube 3: luciferase and ATP solution. Tube 4: boiled luciferase and ATP solution. Light was given out in tube 3 only. Which conclusion do the results support?

Question 15Section 1 style

Which statement describes the role of ATP in cells?

Question 16Section 1 style

When is pyruvate converted to lactate in human muscle cells?

Question 17Section 1 style

Why is the conversion of pyruvate to lactate important to a muscle cell during vigorous exercise?

Question 18Section 1 style

When pyruvate is converted to lactate, hydrogen ions are transferred to the pyruvate. Where do these hydrogen ions come from?

Question 19Section 1 style

Which row describes how the oxygen debt is repaid?

Question 20Section 1 style

A person has an inherited condition in which their muscle cells cannot convert pyruvate to lactate. Which describes the most likely effect during vigorous exercise, when the muscle cells do not get enough oxygen?

Question 21Section 1 style

Which row shows what happens to the hydrogen ions and electrons carried by NADH from glycolysis in a muscle cell at rest and during vigorous exercise, when the cell does not get enough oxygen?

Question 22Section 1 style

Which row describes slow-twitch muscle fibres when they are compared with fast-twitch muscle fibres?

Question 23Section 1 style

How do fast-twitch muscle fibres generate ATP?

Question 24Section 1 style

A thin slice of thigh muscle was treated with a stain that colours the oxygen-storing protein myoglobin dark. Fibres of type X stained dark and fibres of type Y stained pale. Which describes type X fibres?

Question 25Section 1 style

A sample of 250 fibres from the calf muscle of a cyclist contained 175 slow-twitch fibres; the rest were fast-twitch. What is the simplest whole number ratio of slow-twitch to fast-twitch fibres?

Question 26Section 1 style

Muscle samples were taken from two athletes. Sample A contained 320 fibres, of which 65% were slow-twitch. Sample B contained 280 fibres, of which 30% were slow-twitch. How many more fast-twitch fibres were there in sample B than in sample A?

Question 27Section 1 style

A fast-twitch fibre gains a net 2 ATP from each glucose molecule, using glycolysis only. A slow-twitch fibre gains 30 ATP from each glucose molecule by aerobic respiration. Each fibre produces 600 ATP. How many more glucose molecules does the fast-twitch fibre use than the slow-twitch fibre?

Question 28Section 1 style

Blood lactate concentration in mmol per litre. At rest, before the run: 1.2. End of the run: 12.0. 10 minutes after: 8.4. 20 minutes after: 5.4. 40 minutes after: 3.0. 60 minutes after: 1.2.
Time	Blood lactate concentration (mmol l $^{-1}$ )
At rest, before the run	1.2
End of the run	12.0
10 minutes after	8.4
20 minutes after	5.4
40 minutes after	3.0
60 minutes after	1.2

The table shows the concentration of lactate in a runner's blood before and after a 400 metre race. At rest, before the run: 1.2 mmol l

^{-1}

. End of the run: 12.0. 10 minutes after: 8.4. 20 minutes after: 5.4. 40 minutes after: 3.0. 60 minutes after: 1.2. What was the percentage decrease in blood lactate concentration in the first 20 minutes after the run?

Question 29Section 1 style

Samples from the thigh muscles of two elite athletes were examined. In athlete X, 84% of the fibres were slow-twitch. In athlete Y, 22% of the fibres were slow-twitch. Which row most likely matches each athlete to a sport?

Question 30Section 1 style

Which statement about the electron transport chain is correct?

Section 2 style questions

Mealworms in a sealed tubeSection 2 style · 7 marks

A student measured the oxygen uptake of 4.0 g of mealworms at 20 °C with a simple respirometer. The mealworms sat on a gauze above potassium hydroxide solution in a sealed boiling tube, which was joined to a capillary tube holding a drop of coloured liquid. As the mealworms took in oxygen, the drop moved along the capillary tube towards them. Each 1 mm moved by the drop represents 0.5 mm

^{3}

of oxygen taken in. The table shows the distance the drop moved in three runs of 10 minutes each: run 1, 30 mm; run 2, 34 mm; run 3, 32 mm. The student planned to repeat the experiment at other temperatures.

Distance moved by the drop in 10 minutes. Run 1: 30 mm. Run 2: 34 mm. Run 3: 32 mm. Mean: not given.
Run	Distance moved by the drop in 10 minutes (mm)
1	30
2	34
3	32
Mean	?

(a) Calculate the mean distance moved by the drop in 10 minutes, in mm. [1]

Type fractions as 3/8, powers as x^2 and roots as sqrt(5).

(b) Calculate the rate of oxygen uptake by the mealworms, in mm³ of oxygen per g per minute. [2]

Show your working on paper; type the final answer here. Type fractions as 3/8, powers as x^2 and roots as sqrt(5).

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(d) Describe a suitable control for this experiment. [1]

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(e) Identify one variable, other than temperature, that should be kept constant when the experiment is repeated at other temperatures. [1]

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Which sugar does yeast use?Section 2 style · 6 marks

Resazurin is a blue dye that turns pink when it accepts hydrogen ions and electrons removed by dehydrogenase enzymes. A student set up five tubes, each with 5 cm

^{3}

of yeast suspension and 5 cm

^{3}

of a 2% sugar solution, with a different sugar in each tube. The tubes stood in a water bath at 30 °C for 10 minutes. She then added 1 cm

^{3}

of resazurin to each and timed how long it took to turn pink. The table shows her results. Glucose: 8.0 minutes. Fructose: 10.0 minutes. Maltose: 12.0 minutes. Sucrose: 16.0 minutes. Lactose: still blue after 60 minutes.

Time for resazurin to turn pink. Glucose: 8.0 minutes. Fructose: 10.0. Maltose: 12.0. Sucrose: 16.0. Lactose: still blue after 60 minutes.
Sugar	Time to turn pink (minutes)
Glucose	8.0
Fructose	10.0
Maltose	12.0
Sucrose	16.0
Lactose	still blue after 60

(a) Calculate the percentage increase in the time taken to turn pink between glucose and maltose. [1]

Type fractions as 3/8, powers as x^2 and roots as sqrt(5).

(b) Which conclusion about lactose do the results support? [1]

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(d) Describe how the student could improve the reliability of these results. [2]

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Fibres and sportSection 2 style · 8 marks

Small samples of thigh muscle were taken from six elite athletes, and the percentage of slow-twitch fibres in each sample was found. The bar chart shows the results: marathon runner 80%, cross-country skier 75%, road cyclist 70%, 800 metre runner 50%, weightlifter 35% and sprinter 25%. All the other fibres were fast-twitch.

(a) Calculate the simplest whole number ratio of slow-twitch to fast-twitch fibres in the sprinter's sample. [1]

Type fractions as 3/8, powers as x^2 and roots as sqrt(5).

(b) A second sample from the road cyclist contained 360 fibres in the same proportions. Calculate the number of fast-twitch fibres in this sample. [1]

Type fractions as 3/8, powers as x^2 and roots as sqrt(5).

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(d) Explain why a high proportion of fast-twitch fibres suits a sprinter. [2]

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Lactate before and after trainingSection 2 style · 8 marks

A student did the same 12-minute exercise test before and after a 10-week endurance training programme. Exercise stopped at 12 minutes, and blood lactate was measured until 50 minutes. The graph shows the results in mmol l⁻¹. Before training: 1.2 at 0 minutes, 3.0 at 4, 6.0 at 8, 9.0 at 12, 6.6 at 20, 4.2 at 30, 2.4 at 40 and 1.2 at 50. After training: 1.2 at 0 minutes, 2.0 at 4, 3.6 at 8, 5.4 at 12, 3.6 at 20, 2.0 at 30, 1.2 at 40 and 1.2 at 50.

(a) Calculate the percentage decrease in the blood lactate concentration at 12 minutes after training compared with before training. [1]

Type fractions as 3/8, powers as x^2 and roots as sqrt(5).

(b) Before training, how many minutes after exercise stopped did the blood lactate concentration take to return to its value at 0 minutes? [1]

Type fractions as 3/8, powers as x^2 and roots as sqrt(5).

(d) Explain why the blood lactate concentration rose during the exercise test. [3]

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(e) Describe how the oxygen debt is repaid after the exercise. [2]

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Counting ATP with lightSection 2 style · 8 marks

The enzyme luciferase makes luciferin give out light, using energy transferred by ATP; the more ATP present, the more light is given out. Four samples of mitochondria from liver cells were set up, each with a respiratory substrate, and after 5 minutes luciferase and luciferin were added and the light was measured. Sample A: substrate and oxygen, 480 units. Sample B: as A, with a substance that stops electrons passing along the electron transport chain, 30 units. Sample C: as A, with a substance that makes the inner mitochondrial membrane leaky to hydrogen ions, 120 units. Sample D: substrate and no oxygen, 40 units.

Light given out by four samples of mitochondria. A, substrate and oxygen: 480 units. B, as A with a substance that stops electrons passing along the chain: 30. C, as A with a substance that makes the inner membrane leaky to hydrogen ions: 120. D, substrate and no oxygen: 40.
Sample	Light given out (units)
A: substrate and oxygen	480
B: as A, with a substance that stops electrons passing along the chain	30
C: as A, with a substance that makes the inner membrane leaky to hydrogen ions	120
D: substrate, no oxygen	40

(a) Calculate the percentage decrease in the light given out by sample C compared with sample A. [1]

Type fractions as 3/8, powers as x^2 and roots as sqrt(5).

(b) Explain why very little ATP was produced in sample D, which had no oxygen. [2]

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(d) State the role of ATP in cells. [1]

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