7.1.3 Muscle fibre structure, fast and slow twitch fibres Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 7

The 20 questions

1. Which structural feature is characteristic of a muscle fibre?

   • It is a branched cell that has no nucleus and no myofibrils in its cytoplasm
   • It is a long, multinucleate cell that contains many myofibrils running along its length
   • It is a short, uninucleate cell that contains a single myofibril wrapped around its nucleus
   • It is an acellular fibre that is made of collagen and contains no myofibrils at all

2. Which fibre type has a greater density of mitochondria and myoglobin, supporting aerobic respiration?

   • Fast twitch fibres, which contain more glycolytic enzymes and fatigue quickly during activity
   • Slow twitch fibres, which resist fatigue and sustain aerobic activity over long periods
   • Slow twitch fibres, which have few capillaries and fatigue rapidly during sustained activity
   • Fast twitch fibres, which have a large diameter and a high glycogen content

3. Which feature is characteristic of fast twitch muscle fibres?

   • A small diameter and dense capillary network, suited to continuous low-intensity contraction
   • A high concentration of glycolytic enzymes and glycogen, suited to rapid contraction and anaerobic respiration
   • A high concentration of myoglobin and mitochondria, suited to long periods of aerobic exercise
   • A large number of slow myosin heads and a low ATPase activity, suited to posture and standing

4. Which statement compares fast and slow twitch fibres correctly?

   • Fast twitch fibres contract more slowly and resist fatigue, while slow twitch fibres fatigue more quickly
   • Fast twitch fibres have more mitochondria than slow twitch fibres, which makes them more fatigue resistant
   • Fast and slow twitch fibres have identical contraction speeds, but differ only in colour under the microscope
   • Fast twitch fibres contract more rapidly and fatigue faster, while slow twitch fibres contract more slowly and resist fatigue

5. Why do slow twitch fibres appear red?

   • They contain high levels of glycogen, which is stained red during the preparation of the slide
   • They contain high levels of myoglobin, which stores oxygen and gives the muscle a red colour
   • They contain high levels of collagen, which is red in colour and makes the fibres appear firm
   • They are supplied by fewer capillaries, which makes the fibres look pale and red in colour

6. Which structure in a muscle fibre is responsible for conducting the action potential into the centre of the fibre?

   • The sarcoplasmic reticulum, which conducts the action potential along its length
   • The nuclei, which conduct the action potential from the motor neurone into the fibre
   • The myofibrils, which conduct the action potential through the actin filaments
   • The T-tubules, which are invaginations of the sarcolemma

7. Which feature of fast twitch fibres increases their capacity for rapid calcium release?

   • A reduced number of myofibrils, which lets calcium diffuse freely through the cytoplasm
   • A thick sarcolemma with very few T-tubules, which slows the release of calcium
   • A high density of mitochondria, which absorb calcium and prevent it from being released
   • A well-developed sarcoplasmic reticulum, which stores and releases calcium quickly

8. Which muscle fibre type is best suited to a marathon runner's leg muscles during a long race?

   • Fast twitch fibres, which contract powerfully but fatigue quickly during the long race
   • Slow twitch fibres with no mitochondria, which store glycogen for emergency sprinting only
   • Fast twitch fibres with very low myoglobin, which conserve energy during the entire race
   • Slow twitch fibres, which rely on aerobic respiration and resist fatigue over a long period

9. Which muscle fibre type would be most useful for a sprinter's leg muscles in a 100 m race?

   • Fast twitch fibres, which generate high power and rely on anaerobic glycolysis for short bursts
   • Slow twitch fibres, which generate high power and rely on aerobic respiration for short bursts
   • Slow twitch fibres, which have many mitochondria and so release energy most rapidly in short sprints
   • Fast twitch fibres with many mitochondria, which allow sustained aerobic work for the full race

10. A fibre sample from a muscle has many mitochondria and a dense capillary network. Which fibre type is it most likely to be?

    • Fast twitch, since these features show that the fibre is specialised for short bursts of power
    • Fast twitch, since these features support rapid contraction through anaerobic respiration
    • Neither, since mitochondria and capillaries are found only in the cardiac muscle of the heart
    • Slow twitch, since these features support sustained aerobic respiration

11. Which statement evaluates the claim that fast twitch fibres are always better for athletic performance?

    • The claim is accurate, since slow twitch fibres are never used in any athletic event at all
    • The claim is accurate, since fast twitch fibres are better for every type of athletic activity without exception
    • The claim is inaccurate, since fast twitch fibres cannot contract at all in any athletic event
    • The claim is oversimplified, since the best fibre profile depends on the event, from sprinting to endurance running

12. Which statement about fibre type distribution is accurate?

    • Fibre type distribution is fixed at birth and cannot change at all with training or exercise
    • Every muscle has exactly the same proportion of fast and slow twitch fibres in every person
    • Fibre type proportions depend only on the colour of the skin, and not on the function of the muscle
    • Fibre type proportions vary between muscles and between individuals

13. Why does a slow twitch fibre have more capillaries than a fast twitch fibre?

    • To provide a larger surface area for calcium to diffuse out of the sarcoplasmic reticulum
    • To remove more lactate from the fibre during intense contraction, which is its main purpose
    • To supply more oxygen and glucose to the many mitochondria it contains for aerobic respiration
    • To increase the speed of contraction by providing extra blood flow to the myosin heads

14. What is the role of myoglobin in a muscle fibre?

    • It binds oxygen and stores it within the muscle fibre, supporting aerobic respiration
    • It binds calcium ions and holds them in the sarcoplasmic reticulum until contraction begins
    • It breaks down ATP to ADP and phosphate, releasing the energy needed for contraction
    • It carries oxygen in the blood between the lungs and the muscle, as haemoglobin does in red blood cells

15. Which feature is found in both fast and slow twitch fibres?

    • Neither fibre type containing a sarcolemma, which is replaced by a cell wall of cellulose
    • Slow fibres containing only myosin, while fast fibres contain only actin filaments
    • Myofibrils present only in fast twitch fibres, which are absent from slow twitch fibres
    • Myofibrils containing actin and myosin arranged into sarcomeres

16. Which molecule is abundant in fast twitch fibres and provides a store of glucose for rapid anaerobic respiration?

    • Myoglobin, which stores oxygen for prolonged aerobic respiration in slow twitch fibres
    • Collagen, which provides tensile strength to the endomysium surrounding each fibre
    • Keratin, which forms the protective outer layer of the fibre membrane in all cells
    • Glycogen, which is stored in the sarcoplasm and broken down rapidly to supply glucose

17. A muscle fibre has high myosin ATPase activity and fatigues quickly. Which fibre type is it most likely to be?

    • Slow twitch, since myoglobin is found only in the fast twitch fibres of the body
    • Fast twitch, since high ATPase activity and rapid fatigue match the properties of fast fibres
    • Neither, since myosin ATPase is absent from all skeletal muscle fibres in the body
    • Slow twitch, since high ATPase activity and rapid fatigue match the properties of slow fibres

18. One slow twitch fibre contains 400 mitochondria and one fast twitch fibre contains 100. How many times more mitochondria does the slow fibre contain?

    • Forty times as many, since 400 divided by 10 gives 40 times the number in the fast fibre
    • Three times as many, since 400 minus 100 gives 300 and 300 divided by 100 is 3
    • Equal numbers, since mitochondria are not affected by the type of muscle fibre in the body
    • Four times as many, since 400 divided by 100 is 4

19. Which evidence best supports the claim that the properties of muscle fibres can be altered by training?

    • Endurance training increases mitochondrial density and capillary supply within the trained muscle fibres
    • Sprint training reduces the diameter of all fibres to the same size across the muscle
    • Training increases the number of muscle fibres after the age of 25, so new fibres form throughout life
    • Training has no effect on fibre properties and only changes the overall length of the muscle

20. Which feature allows slow twitch fibres to keep contracting for long periods?

    • A poorly developed sarcoplasmic reticulum that conserves calcium during repeated contractions
    • A large number of lactate-producing enzymes that generate ATP without oxygen
    • A large diameter and high glycogen store that supports fast anaerobic contractions
    • A dense supply of mitochondria and capillaries that sustains aerobic ATP production

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