Muscles

Question 1

Describe the banding pattern in striated muscles (3)

Answer 1

1. Lightest band is I band, actin only
2. Darkest band is overlapping region, actin and myosin
3. Medium shading is H zone, myosin only

Question 2

Describe the sliding filament theory (4)

Answer 2

1. Cross bridges between actin and myosin heads
2. Power stroke of myosin heads
3. Detachment of myosin heads
4. Myosin heads move back, recovery stroke

Question 3

Describe the function of Calcium ions in muscle contraction (4)

Answer 3

1. Ca2+ binding
2. Exposes actin binding sites
3. Myosin head attaches and forms cross bridges
4. Activates ATP hydrolase

Question 4

Nerve impulses arriving at the presynaptic membrane at the neuromuscular junction result in shortening of sarcomeres. Describe how. (6)

Answer 4

1. Ca2+ enter pre synaptic membrane
2. Vesicle fuses with membrane
3. Neurotransmitter diffuses
4. Binds to receptors on post synaptic membrane
5. Leads to depolarisation so Na+ enter
6. Release Ca2+
7. Removes tropomyosin and exposes actin binding sites
8. Actinomyosin cross bridges form
9. Myosin head moves and pulls actin along
10. ATP hydrolase activated

Question 5

Explain the important of ATP hydrolase in muscle contraction (2)

Answer 5

1. Hydrolysis of ATP releasing energy
2. Used to form actinomyosin cross bridges

Question 6

Muscle contraction requires ATP. What are the advantages of using aerobic rather than anaerobic respiration to provide ATP in a long-distance race? (4)

Answer 6

1. Aerobic respiration produces more ATP
2. Less lactate
3. Avoids muscle cramps
4. CO2 easily removed

Question 7

A muscle fibre contracts when it is stimulated by a motor neurone. Describe how transmission occurs across the synapse between a motor neurone and a muscle fibre (6)

Answer 7

1. Ca2+ channels open
2. Ca2+ enter pre synaptic neurone
3. Vesicles move and fuse with presynaptic membrane
4. Release acetylcholine
5. Diffuses across synaptic cleft
6. Binds to receptors in post synaptic membrane
7. Na+ channels open and Na+ enter

Question 8

After death, cross bridges between actin and myosin remain firmly bound. Explain what causes the cross bridges to remain firmly bound (3)

Answer 8

1. Respiration stops
2. No ATP produced
3. ATP required for separation of actinomyosin cross bridges

Question 9

Describe the role of Calcium ions in the contraction of a sarcomere (4)

Answer 9

1. Interact with tropomyosin
2. Reveals binding sites on actin
3. Allowing myosin heads to bind
4. Activate ATP hydrolase

Question 10

Describe slow twitch muscle fibres (5)

Answer 10

1. Lots of mitochondria for aerobic respiration
2. More myoglobin
3. Less glycogen as glucose fully broken down
4. Less extensive sarcoplasmic reticulum
5. Less stores of phosphocreatine

Question 11

Describe fast twitch muscle fibres (6)

Answer 11

1. Used for rapid contractions
2. Phosphocreatine used up rapidly to make ATP
3. Anaerobic respiration
4. ATP used to form phosphocreatine
5. Lots of phosphocreatine
6. No myoglobin

Question 12

Describe the role of phosphocreatine (2)

Answer 12

1. Provides phosphate
2. To make ATP from ADP and Pi

Question 13

Describe the part played by tropomyosin in myofibril contraction (2)

Answer 13

1. Moves out of the way when Ca”+ binds
2. Allows myosin to bind to actin binding site

Question 14

Describe the part played by myosin in myofibril contraction (2)

Answer 14

1. Myosin head binds to actin and pulls actin
2. Detaches from actin and re-sets
3. Uses ATP

Question 15

Explain why the increased cardiac output is an advantage during exercise (4)

Answer 15

1. In exercise, more aerobic respiration
2. Higher cardiac output so increase oxygen supply to muscles
3. Increase glucose supply to muscles
4. Increase CO2 removal from muscles

Question 16

Glycogen granules are present in skeletal muscles. Explain their role in skeletal muscles (2)

Answer 16

1. Hydrolysed to glucose
2. For respiration to provide ATP

Question 17

During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of Ca2+ ions to stimulate muscle contraction. Suggest how (5)

Answer 17

1. Low pH changes shape of calcium ion receptors
2. Fewer calcium ions bind to tropomyosin
3. Fewer tropomyosin molecules move away
4. Fewer binding sites on actin revealed
5. Fewer cross-bridges can form

Question 18

What is the role of ATP in myofibril contraction? (2)

Answer 18

1. Allows binding of myosin to actin to form actinomyosin bridge
2. Provides energy to move myosin head

Question 19

Describe the role of calcium ions and ATP in the contraction of a myofibril (6)

Answer 19

1. Calcium ions diffuse into myofibrils from sarcoplasmic reticulum
2. Calcium ions cause movement of tropomyosin
3. Exposes actin binding sites
4. Myosin heads attach to actin binding sites
5. Hydrolysis of ATP causes myosin heads to bend
6. Bending pulls actin molecules
7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach from actin sites