Skeletal Muscles

Question 1

Muscles act in ______________ pairs against an incompressible skeleton

Answer 1

antagonistic

Question 2

Individual muscles are made up of many fibres - the specialised cell of the muscle. These cells are very long, [1] and surrounded by a cell surface membrane called the [2]

Answer 2

[1] multinucleated

[2] sarcolemma

Question 3

Within each muscle fibre there are many [1] which contain the contractile proteins [2] and myosin. There are also many [3] to produce ATP.

Answer 3

[1] myofibrils

[2] actin

[3] mitochondria

Question 4

Which organelle surrounds the myofibrils and

Answer 4

Sacroplasmic reticulum

Question 5

Protein that blocks myosin head binding sites on actin

Answer 5

Tropomyosin

Question 6

Describe the role of calcium ions in the contraction of a myofibril (3 marks).

Answer 6

1. Calcium ions diffuse into myofibrils from sarcoplasmic reticulum;
2. Cause movement of tropomyosin (on actin);
3. This movement exposes binding sites on actin;
4. Myosin heads attach to binding sites on actin;

Question 7

When myosin heads bind to actin, this is called a ____________ bridge.

Answer 7

actinomyosin

Question 8

Describe the roles of ATP in muscle contraction (3 marks).

Answer 8

(Hydrolysis of ATP releases energy which…)

1. Moves/bends the myosin head;
   .
2. So actin filaments are moved/pulled inwards (towards the centre of the sarcomere);
3. A new ATP binds to myosin heads and breaks actinomyosin bridges;
4. For active transport of calcium ions (into the sarcoplasmic reticulum);

Question 9

Describe the roles of calcium ions and ATP in the contraction of a myofibril (5 marks)

Answer 9

1) Ca2+ diffuse into myofibrils from sarcoplasmic reticulum
2) Ca2+ cause movement of tropomyosin on actin
3) this movement causes exposure of the binding sites on actin
4) myosin heads attach to binding sites on actin
5) hydrolysis of ATP on myosin heads causes myosin heads to bend
6) bending pulling actin molecules
7) attachment of a new ATP molecule to each myosin head causes myosin heads to detach

Question 10

Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction (3 marks).

Answer 10

1. Less / no tropomyosin moved from myosin head bind sites on actin
2. Fewer / no actinomyosin bridges formed
3. Myosin head does not move

OR myosin head does not pull action

Question 11

Creatine + phosphate =

Answer 11

Phosphocreatine

Question 12

What is the role of phosphocreatine in providing energy during muscle contraction? (2 marks)

Answer 12

Provides phosphate
Which is required to produce ATP

Question 13

Some studies have suggested that taking creatine supplements can improve muscle performance during intense short-term exercise.

Describe and explain how taking creatine supplements can improve performance of different types of muscle fibres during different types of exercise (2 marks).

Answer 13

1. Fast skeletal muscle fibres used during short-term/intense exercise;
2. Creatine used to form phosphocreatine;
3. Phosphocreatine combines with ADP to form ATP;

Question 14

In muscles, pyruvate is converted to lactate during prolonged exercise.

Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration.

Answer 14

1. Regenerates/produces NAD

OR oxidises reduced NAD;

2. So glycolysis continues;

Question 15

Properties of slow-twitch muscle fibres

Answer 15

Contract more slowly

Produce less force

Fatigue less quickly (due to less lactate production)

Suited to endurance activities like walking and perching

Ideal for animals that migrate or engage in long-distance activities (e.g., wings of migrating geese, legs of wolves)

Question 16

Structure of slow-twitch muscle fibres

Answer 16

Rely on aerobic respiration for ATP production

Many large mitochondria

Myoglobin dissociates from oxygen at very low partial pressures (provides an emergency supply of oxygen and also gives these fibres their red colour)

Denser network of capillaries for increase blood supply so efficient oxygen and glucose supply

Question 17

Properties of fast-twitch muscle fibres

Answer 17

Contract faster

Produce more force

Fatigue quickly (due to lactate production)

Suited to short bursts of high-intensity activity e.g sprinting and weight lifting

Common in animals’ limbs used for escaping predators or hunting prey (e.g., robin’s wings, cheetah’s legs).

Question 18

Structure of fast-twitch muscle fibres

Answer 18

Rely on anaerobic respiration for ATP production

Higher concentrations of glycogen

Larger stores of phosphocreatine

Fewer capillaries

Question 19

Describe and explain how eating more carbohydrate, known as ‘carbohydrate loading’, for a few days before exercise can improve muscle performance of different muscle fibres when exercising for a long time (3 marks).

Answer 19

1. Fast (skeletal muscle) fibres used during short-term/intense exercise;
2. Slow (skeletal muscle) fibres used during long(er)-term exercise;
3. (Carbohydrate/glucose) stored as glycogen

OR Glycogenesis;

4. Glycogen hydrolysed to glucose

OR Glycogenolysis;

5. Glucose for respiration;

Question 20

Explain the role of glycogen granules present in skeletal muscle (2 marks).

Answer 20

1. As a store of glucose

OR To be hydrolysed to glucose;

2. For respiration / to provide ATP;

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Question 21

Fast muscle fibres have a higher concentration of glycogen than slow muscle fibres.

Explain how the difference in glycogen concentration is related to the different properties of these muscle fibres.

Answer 21

1. Fast fibres contract quickly whereas slow fibres contract slowly

OR fast used for shorter time OR slow used for longer time;

2. Fast fibres mainly use anaerobic respiration whereas slow fibres use aerobic respiration;

3 Fast fibres produce ATP quickly whereas slow fibres produce ATP slowly

OR less ATP/energy (per glucose) from anaerobic respiration

More ATP/energy (per glucose) from aerobic respiration

4. Glycogen is a store of glucose OR glycogen hydrolysed to glucose;