Skeletal Muscles (A Level only) (AQA A Level Biology)

Exam Questions

3 hours15 questions
1a3 marks

Muscle fibres consist of many muscle cells fused together. As well as sharing nuclei, muscle fibres share ___________, which contains many mitochondria. Each fibre is made up of myofibrils which contain 2 types of protein; _________ which is thinner and __________ which is thicker.

1b2 marks

Define the term antagonistic muscle action.

1c2 marks

Figure 1 shows a myofibril strand in a relaxed muscle fibre.

Figure 1

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Describe the effect of muscle fibre contraction on the length of the A-band and the sarcomere.

1d2 marks

Explain the presence of a large number of mitochondria in the sarcoplasm of a muscle fibre.

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2a2 marks

The basic structure of skeletal muscle can be observed under an optical microscope. Measurements of cells are taken using an eyepiece graticule.

Describe how an eyepiece graticule can be calibrated.

2b2 marks

Figure 1 shows an eyepiece graticule alongside a stage micrometer with 10 μm divisions.

Figure 1

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Use Figure 1 to calculate the size of one division of the graticule. 

2c2 marks

Using the information calculated in part (b), find the width of cell B in Figure 2.

Figure 2

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2d2 marks

Suggest two reasons why it may be beneficial to study skeletal muscle fibres using an electron microscope rather than an optical microscope.

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3a2 marks

Figure 1 shows the sequence of events that lead to muscle contraction.

Figure 1

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Describe the part played by tropomyosin during contraction.

3b2 marks

Identify the role of phosphocreatine in providing energy during muscle contraction.

3c3 marks

Complete Table 1 to identify the molecules that carry out the function described.

Table 1

Function

Name of molecule

Hydrolyses ATP

 

Covers the binding site on the actin filament (when the muscle is relaxed)

 

Required for recocking of the myosin head

 

3d2 marks

State the role of calcium ions during muscle contraction.

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4a2 marks

A muscle fibre is 30 mm long when relaxed, but only 22.5 mm long when contracted.

Calculate the percentage decrease in length of the contracted muscle.

4b2 marks

If each sarcomere is 2.5 μm long in a contracted muscle fibre, calculate how many sarcomeres would be found along the whole length of the contracted muscle fibre discussed in part a.

4c3 marks

Continued and prolonged exercise can result in muscle fatigue due to a decrease in the availability of calcium ions.

Explain why a decrease in the availability of calcium ions would result in a decrease in the strength of muscle contraction.

4d2 marks

State the reason for high levels of glycogen in fast muscle fibres.

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5a2 marks

Fast muscle fibres have fewer capillaries than slow muscle fibres. Explain why.

5b2 marks

Suggest why slow muscle fibres contain a large amount of myoglobin.

5c2 marks

Figure 1 shows the composition of a bundle of muscle fibres. The fast fibres are lightly shaded and the slow fibres are darkly shaded.

Figure 1

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Calculate the ratio of slow to fast muscle fibres for this bundle of muscle fibres.

5d2 marks

Compare the structure of the protein filaments, actin and myosin.

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1a3 marks

Figure 1 below is a transmission electron micrograph of a longitudinal section of skeletal muscle.

Figure 1

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Name structures X, Y and Z.
1b1 mark

State the name of the structure found between points 1 and 2.

1c4 marks

During intense exercise the pH of skeletal muscle tissue falls sharply. This decrease in pH reduces the ability of calcium ions to stimulate muscle contraction.

Suggest how.

1d3 marks

Figure 2 below shows a neuromuscular junction. 

Figure 2

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Explain why one action potential arriving at this neuromuscular junction might not cause a contraction but several arriving in succession might.

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2a3 marks

Scientists investigated whether the blood supply to slow and fast muscle fibres in a muscle differed between sexes. They used diaphragms taken from mice as the diaphragm is constantly in use for breathing. Diaphragms were taken from groups of adult male and female mice. A sample of muscle tissue was taken from each diaphragm and examined under an optical microscope. For each sample, they selected several fields of view at random. In each field of view, the number of capillaries associated with each type of muscle fibre was counted and recorded.

This allowed scientists to calculate the mean number of capillaries for each type of muscle fibre, for males and females. Table 1 below shows the results which include standard deviation (SD).

Table 1

Sex 

Number of mice in a group

Mean number of capillaries associated with each type of muscle fibre
Slow fibres (± SD)
Fast fibres (± SD)

Female

10

3.7
(±0.7)
4.1
(±0.8)

Male

11

4.9
(±0.3)
6.4
(±0.2)

Give three precautions that the scientists took to ensure their calculations of mean number of capillaries per fibre were reliable.

2b2 marks

The researchers examined the muscle of an animal in the female age group. They found one field of view contained only slow muscle fibres. They counted 63 capillaries in this field of view. Use a calculation to estimate how many slow muscle fibres were visible in this field of view. Show your working.

2c3 marks

A research assistant concluded that sex had a significant effect on the mean number of capillaries per muscle fibre. How do the results support this conclusion?

2d4 marks

Give four differences between slow and fast muscle fibres.

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3a2 marks

Describe the role of phosphocreatine in supplying energy during muscle contraction.

3b3 marks

Researchers investigated the time taken for phosphocreatine (PC) to be re-formed in leg muscles after a certain amount of exercise in healthy people of different ages. The exercise involved short, fast contractions of the leg muscles. Figure 1 below shows the results. Each dot is the result of a single individual.

Figure 1

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There is a large degree of variation in the time taken for phosphocreatine to be re-formed in people of a very similar age. Suggest three possible reasons for this variation.

3c5 marks

Describe and explain the data seen in Figure 1.

3d2 marks

Describe what a tendon is and its function.

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4a5 marks

Describe the events in the cycle of actinomyosin bridge formation.

4b4 marks

Describe what happens to the length of the A band and the I band when the sarcomeres contract. Explain your answer. 

4c3 marks

Complete Table 1 below by identifying the appropriate molecules.

Table 1

Function

Name

Attaches to M line at the centre of the sarcomere

 
Hydrolysis of this molecule is required for the recovery stroke

 
Ion that diffuses across the sarcolemma

 

4d2 marks

Describe an antagonistic pair of muscles.  Give an example.

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5a4 marks

It is thought that each human is born with a certain proportion of slow and fast muscle fibres in their skeletal muscles. Most individuals have roughly half “fast fibres” and half “slow fibres”.

A sports researcher predicted that these proportions would change over time depending on the type of activity/sport a person trained in. 

The following facts were established before the researcher’s investigation: the number of muscle fibres in a skeletal muscle remains constant over time but the number of mitochondria within a fibre can change and the diameter of fibres can also change.

She calculated the mean percentages of fast and slow fibres in skeletal muscles of different athletes. The results are shown in Figure 1 below in the form in which he presented them.

Figure 1

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Predict which athlete type the sports scientist would expect to find muscle fibres with the lowest number of mitochondria? Justify your answer.

5b2 marks

A research assistant reviewed the results and stated that “regular powerlifting changes your proportion of slow and fast skeletal muscle fibres.” Do you agree with this statement? Explain your answer.

5c3 marks

The arm muscles of long-distance swimmers are usually larger than the arm muscles of non-athletes. Suggest why.

5d3 marks

Ultra long-distance swimmers may suffer from muscle fatigue when the contraction mechanism of muscles is disrupted. One reason for this thought to be a decrease in the availability of calcium ions within muscle fibres. Explain how a decrease in the availability of calcium ions could disrupt the contraction of muscles.

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1a5 marks

Malignant hyperthermia (MH) is a dangerous condition during which a patient’s skeletal muscles become contracted and rigid. It is caused by a mutation in the gene that codes for intracellular calcium channels. MH is difficult to diagnose until it is triggered by the administration of an anaesthetic.

Suggest how the anaesthetic combined with the MH mutation could lead to contracted skeletal muscles in a patient.

1b3 marks

Figure 1 shows some of the physiological effects that take place after the administration of an anaesthetic to a patient who is MH susceptible. End Tidal Carbon Dioxide refers to the amount of carbon dioxide released during an exhaled Breath.

Figure 1

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Use your knowledge of the events taking place inside a contracting skeletal muscle to explain the effects on the graph between 0 and 150 minutes after the administration of an anaesthetic

1c2 marks

MH is a very dangerous condition that can be fatal if not treated quickly. Use the information provided and your own knowledge to explain why MH can be fatal.

1d2 marks

At point X on Figure 1 a life-saving drug called Dantrolene was administered. Suggest how Dantrolene might counteract the effects of the anaesthetic.

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2a4 marks

Figure 1 below shows a cross section through a skeletal muscle.

Figure 1

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Identify structures A-D labelled on Figure 1.

2b3 marks

The structures labelled E in Figure 1 above are called myofibrils. When myofibrils are viewed in longitudinal section they have a striped, or striated, appearance and are made up of manysarcomeres. Two sarcomeres are shown in Figure 2 below. 

Figure 2

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The myofibril is 4.5cm in length when it is relaxed, while a contracted sarcomere measures 1.9μm. 

Use the scale on Figure 2 to calculate the length of a contracted myofibril (the image measurements are provided for you). Give your answer in mm.

2c2 marks

The striated pattern visible on the sarcomeres is due to the presence of two types of filament within the myofibril. These filaments are known to be involved with muscle contraction, but a relatively recent discovery has shown that a third protein filament known as titin, is also present. The role played by titin is still being investigated, but one study was carried out in mice that looked at the effects of removing titin from their muscles.

To remove the titin protein, the mice had their muscles modified so that their titin filaments contained a cutting site for a plant enzyme called TEV protease.

Suggest why the plant enzyme TEV was used rather than an animal protease.

2d3 marks

Figure 3 below shows the location of titin within the sarcomere, as well as some of the results gained from the study described in part c) above. 

Figure 3

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Use Figure 3 and your existing knowledge to suggest 3 possible functions of titin filaments

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3a2 marks

Figure 1 below shows the relationship between muscle fibre diameter and oxidative capacity (ability to use oxygen).

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Suggest an explanation for this relationship.

3b4 marks

Research has shown that larger animals tend to have a higher proportion of muscle fibres with a larger diameter, and that these large-diameter fibres are fast muscle fibres, while slow fibres are narrower in diameter.

Figure 2 shows the relationship between body mass in mammals and reptiles and their running speed. 

Figure 2

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Suggest an explanation for the relationship shown in Figure 2 between body mass and speed in mammals.

3c3 marks

Reptiles often have a different angle between their legs and body compared to mammals, and this is often suggested as a reason for the difference in average maximum speed attained by mammals and reptiles of equivalent body mass.

Suggest and explain one other reason for the difference in average maximum speed between mammals and reptiles of equivalent body mass.

3d2 marks

A researcher used a light microscope to calculate the mean diameter of the muscle fibres in rats. The microscope used had a field of view with a circular area of 1.5mm2and 12 muscle fibres were visible in cross-section when looking down the microscope.

Use this information and the equation provided to calculate the mean diameter of a rat muscle fibre. Give your answer in µm.

The area of a circle = π r2

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4a4 marks

Curare is the name given to a collection of plant compounds that have been used historically as both poisons and as muscle relaxants for medical procedures. Curare is known to act at neuromuscular junctions to bring about paralysis.

Suggest how curare might affect the neuromuscular junctions to bring about muscle paralysis.

4b2 marks

Figure 1 below shows a set of structures called the T-tubules which play an important role at the neuromuscular junction. Use Figure 1 to suggest how the T-tubules help in the initiation of a muscle contraction.

Figure 1

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4c2 marks

Figure 2 shows the events that take place after a muscle is stimulated and contraction begins.

Figure 2

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Use the information in Figure 2 and your own knowledge to explain the role played by ATP in muscle contraction. 

4d2 marks

Each round of myosin binding, power stroke and resetting requires the hydrolysis of one molecule of ATP. If a single round moves an actin filament by 35 nm and a full muscle contraction moves an actin filament by 0.49 µm, calculate the number of ATP molecules required for this full contraction to take place.

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5a3 marks

A group of scientists wanted to find out about the effect of a protein known as TWEAK on exercise capabilities in mice. They compared 6 mice with a normal TWEAK gene (described as wild-type) with 6 mice in which the TWEAK gene function had been removed (described as TWEAK-KO). Some of their results are shown below. 

Figure 1

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* = numbers vary significantly between wild-type and TWEAK-KO

The researchers concluded that TWEAK-KO mice had improved exercise tolerance. 

Use Figure 1 and the information provided to evaluate this conclusion.

5b2 marks

The researchers also carried out tests on the muscle cells of the mice, testing for the presence of an enzyme called succinate dehydrogenase (SDH) that is found in the mitochondria. They stained the muscle tissue using a stain that attaches to SDH. Their results are shown in Figure 2.

Figure 2

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Muscle fibre X, and those that look like it, are slow muscle fibres. Explain how this can be concluded only from information found in Figure 2

5c3 marks

The SDH stain shows as being darker in colour in areas where more SDH is present. 

State what Figure 2 shows about SDH distribution inside muscle fibres, and suggest an explanation for this distribution.

5d3 marks

Explain how the difference between wild-type and TWEAK-KO muscle fibres shown in Figure 2 can account for the results shown in Figure 1.

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