Muscle & Motility (HL IB Biology)

The image below shows an electron micrograph cross section through a skeletal muscle.

 Identify structures A-C labelled in the image above.

The structures labelled E in the image in part a) are called myofibrils.

Describe the structure of a myofibril.

The structure labelled C in the image in part a) is 30 mm long when relaxed, but only 22.5 mm long when contracted.

Calculate the percentage decrease in length of the contracted structure C.

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

The image below is a transmission electron micrograph of a longitudinal section of skeletal muscle.

 Identify structures X, Y and Z.

Identify the molecules present in the regions labelled 1 and 2 in the image in part a).

Outline how the filaments within muscle fibres slide past each other in the sliding filament mechanism of muscle contraction.

A recent discovery has shown that a third protein filament, known as titin, is also present in muscle fibres. The role played by titin is still being investigated, but one study looked at the effects of removing titin from the muscles of mice.

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. This meant that the scientists could use TEV protease to cut the titin proteins.

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

The image 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.

Use the image and your existing knowledge to suggest a possible function of titin filaments.

One mark is available for clarity of communication throughout this question.

Draw a labelled diagram of a sarcomere.

Describe the mechanism of muscle contraction from the point at which myosin binds to actin.

The graph 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.

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. 

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.

When myofibrils are viewed in longitudinal section they have a striped, or striated, appearance and are made up of many sarcomeres. Two sarcomeres are shown in the diagram below.

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

Use the scale on the diagram above to calculate the length of a contracted myofibril (the image measurements are provided for you).

State your answer in mm.

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.

A 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.

Flexion of the elbow involves contraction of the biceps to bring the hand upwards when performing a manual action, for example when scratching the nose. 

Aside from the role played by the triceps in extending the arm afterwards, suggest two advantages to having the system of an antagonistic pair of muscles in arm movement. 

The image below shows some of the muscles in the human lower leg. 

Use the diagram and your knowledge of antagonistic pairs to identify the muscles involved in the following motions:

Dorsiflexion - moving the toes upwards towards the shin

Plantar flexion - moving the toes away from the shin e.g. when standing on tiptoe

A technique called electromyography uses electrodes placed onto the skin close to major skeletal muscles. The electrodes measure electrical activity in those muscles and in their surrounding nervous connections. 

The diagram below is an electromyograph trace combined from electrodes placed on a person's left and right gastrocnemius muscles (see diagram in part b for the location of that muscle) taken while the person was walking at an even pace. 

Assuming a mean stride length of 75cm, calculate the person's walking speed.

State your answer in kilometres per hour / kmh^-1.

Explain why tendons need to be inelastic. 

Synovial fluid plays an important role in musculoskeletal movement.

One feature of synovial fluid is that it is classed as a non-Newtonian fluid. This means that it changes its viscosity according to the surrounding conditions.  

Suggest and explain one function of a joint that is aided by synovial fluid being a non-Newtonian fluid. 

Osteoarthritis is a common condition of the joints in which cartilage becomes thinned and eventually wears away. 

Suggest two symptoms of osteoarthritis.