Unit 6 - Muscles

Question 1

Describe the roles of ATP in muscle contraction. (4)

Answer 1

(a) 1. To break actinomyosin (bridges);
Accept ‘to form actinomyosin’.
Accept ‘to detach or attach myosin and actin’.
Reject reference to ‘active site’.
2. To move/bend the myosin head/arm;
Accept ‘to change shape of myosin head/arm’.
Accept ADP/Pi moves (myosin) head/arm.
Accept powerstroke/pivot /recocks etc. for movement.
3. (So) actin (filaments) are moved (inwards);
Ignore ‘sliding’.
4. For active transport of calcium ions (into the sarcoplasmic/endoplasmic reticulum);

Question 2

ATP is essential for muscle contraction. The concentration of ATP in skeletal
muscle is approximately 5 × 10–3 mmol g–1. During maximum exercise, ATP in
skeletal muscle is used at a rate of approximately 3.7 mmol kg–1 s–1. If ATP
was not resynthesised, maximum exercise would last a short time. (2)

Answer 2

(b) 1.35 OR 1.4;

Question 3

Some studies have suggested that taking creatine supplements can improve
muscle performance during intense short-term exercise. Eating more
carbohydrate, known as ‘carbohydrate loading’, for a few days before exercise
can improve muscle performance when exercising for a long time.

Describe and explain how taking creatine supplements (lines 5–6) and ‘carbohydrate loading’ can improve performance of different types of muscle fibres during different types of exercise(5)

Answer 3

1. Fast (skeletal muscle) fibres used during short-term/intense exercise;
   1 and 2 Accept examples of short-term/intensity exercise e.g. sprint and longer-term/endurance exercise, e.g. marathon or low(er) intensity exercise.
   Accept fast twitch fibres for fast (skeletal muscle) fibres
2. Slow (skeletal muscle) fibres used during long(er)-term exercise;
   Accept slow twitch fibres for slow (skeletal muscle) fibres.
3. Creatine used to form phosphocreatine;
4. (Phosphocreatine) combines with ADP to form ATP;
5. (Carbohydrate/glucose) stored as glycogen
   OR Glycogenesis;
6. Glycogen hydrolysed to glucose
   OR Glycogenolysis;
7. Glucose for respiration;
   Accept glycolysis for respiration.
   Max 3 marks from mark points 3, 4, 5, 6 and 7.
   5 max

Question 4

During aerobic exercise, calcium ions in muscle cells have several roles.
They activate the inclusion of glucose transport proteins, GLUT4, in the
cell-surface membrane and the inclusion of fatty acid transport proteins, CD36,
in mitochondrial membranes. An increase in muscle activity increases the
concentration of carbon dioxide in the blood. This causes an increase in
heart rate.

Suggest and explain how GLUT4 and CD36 transport proteins are beneficial during exercise.

Answer 4

1. (More) glucose enters (muscle) cells;
   Ignore more glucose leaves (liver) cells.
   Reject glucose enters mitochondria.
2. (Glucose/fatty acids enter by) facilitated diffusion;
   Accept active transport or cotransport.
3. Fatty acids used in Krebs cycle;
   Ignore gluconeogenesis.
4. Respiration provides (more) ATP;
   Accept in context of glucose or fatty acids.
   Accept for fatty acids ‘Krebs cycle produces ATP’.
   Max 2 marks if only in context of glucose or only in context of fatty acids.

Question 5

An increase in muscle activity causes an increase in heart rate.
Describe and explain how. (4)

Answer 5

1. Increase in CO2 detected by chemoreceptors;
   Accept increase in acidity/H+ or decrease in pH for increase in CO2.
   Ignore location of chemoreceptors.
2. Send (more) impulses to cardiac centre
   OR
   Send (more) impulses to the medulla;
   2 and 3 Reject reference to ‘an/one impulse’ once only.
   2 and 3 Reject ‘signals’, ‘messages’ for ‘impulses’ once only.
   2 and 3 Accept ‘action potentials’ for impulses.
3. More impulses (from centre/medulla) along sympathetic pathway/neurones/nerves
   OR
   Fewer impulses (from centre/medulla) along parasympathetic/vagus pathway/neurones /nerves;
4. (To) SAN;

Question 6

Myasthenia gravis (MG) is an autoimmune disease caused when antibodies bind to the sarcolemma (postsynaptic membrane) of neuromuscular junctions. This can weaken contraction of muscles.

Mestinon is a drug that inhibits the enzyme acetylcholinesterase. Mestinon can help in the treatment of MG.

Suggest and explain how MG can weaken contraction of muscles. Do not include details of myofibril or muscle contraction in your answer. (2)

Answer 6

1. Less/no acetylcholine/neurotransmitter binds to receptor/s;

Accept abbreviations for acetylcholine e.g. ACh, Ach, AChol

Ignore competitive inhibition but reject ‘active site’.

2. Less/no depolarisation

OR Fewer/no action potential(s)

OR Fewer/no sodium ions enter to reach threshold;

Accept ‘takes longer for depolarisation or action/generator potential to be produced’.

Ignore ‘weaker action potential/depolarisation’.

Accept Na+ for sodium ions.

Question 7

Myasthenia gravis (MG) is an autoimmune disease caused when antibodies bind to the sarcolemma (postsynaptic membrane) of neuromuscular junctions. This can weaken contraction of muscles.

Mestinon is a drug that inhibits the enzyme acetylcholinesterase. Mestinon can help in the treatment of MG.

Mestinon can help in the treatment of MG. Explain how. (3)

Answer 7

1. Less/no acetylcholine/neurotransmitter broken down;

Accept (more) acetylcholine/neurotransmitter present/remains.

Accept acetylcholine/neurotransmitter remains attached to receptors (for longer) = 2 marks.

2. (More) acetylcholine attaches to receptors;

Accept acetylcholine/neurotransmitter remains attached to receptors (for longer) = 2 marks.

3. Depolarisation (of sarcolemma) occurs

OR Action potential(s) produced

OR (Enough) sodium ions enter to reach threshold

OR Fewer/no antibodies attach;

Question 8

As humans age, there is a decrease in body protein.

Give the name of one body protein that could have resulted in:

reduced muscle power ________________________________________________

reduced immunity ____________________________________________________ (2)

Answer 8

1. Actin/myosin/tropomyosin;

Accept troponin Accept ATP synthase/hydrolase

2. Antibodies;

Accept immunoglobulins Accept lysozyme

Question 9

The iris in the human eye is a muscular structure. The iris changes the size of the pupil.

The diagram below shows the muscles in the iris.

(a) Suggest and explain how the interaction between the muscles labelled in the diagram above could cause the pupil to constrict (narrow). (2)

Answer 9

1. Circular muscle contracts;
2. Radial muscle relaxes;

Accept, for one mark ‘both muscles contract’ or ‘both muscles relax’ as names of muscles are in the diagram.

Reject muscles constrict.

Question 10

The diagram below shows the banding pattern of a single sarcomere.

Explain the banding pattern shown in the diagram above. (3)

Answer 10

1. Light/I band only actin;
2. H zone/band only myosin;
3. Darkest/overlapping region actin and myosin;

Accept any suitable descriptions that distinguishes these regions e.g. ‘white band’ for 1, ‘light grey’ for 2 and ‘dark grey’ for 3.

Ignore references to A band.

Question 11

Creatinine is produced in muscle tissues. Creatinine diffuses into the blood. The kidneys then excrete creatinine. A calibration curve can be used to determine the concentration of creatinine in urine. One method of producing a calibration curve needs:

• creatinine solution of known concentration
• distilled water
• creatinine-detecting solution
• a colorimeter.

Creatinine-detecting solution reacts with creatinine to produce an orange colour. Use the information provided to describe how you could produce a calibration curve for creatinine. Do not include details on the use of glassware in your answer. (5)

Answer 11

1. Use (distilled) water and creatinine solution to produce dilutions (series);

Accept description of dilutions (series).

2. Addition of (creatinine-)detecting solution (to each solution);

The addition of a known/specific volume of (creatinine-)detecting solution = 2 marks.

3. Using a known/specified/constant volume of a solution (e.g. diluted creatinine solution);

The addition of a known/specific volume of (creatinine-)detecting solution = 2 marks.

4. Record absorbance/transmission of solution/s using a colorimeter;

Reject calorimeter.
Accept description of absorbance or transmission.

5. Plot dilution/concentration of (creatinine) solution against absorbance/transmission;

Accept absorption for ‘absorbance’. Accept description of absorbance or transmission.

Question 12

Describe how you would determine the concentration of creatinine in a urine sample using your calibration curve. (2)

Answer 12

1. Use same volumes of solutions as used in producing (calibration curve)

OR Add (creatinine-)detecting solution (to urine);

Ignore ‘add indicator’ on its own.

Ignore calorimeter in this part of the question.

2. Read off (creatinine) concentration against absorbance/transmission (value) obtained;

Ignore ‘line of best fit’.

Accept ‘compare’ for ‘read off’.

Question 13

A group of scientists suggested that a decrease in the force of muscle contraction is caused by an increase in the concentration of inorganic phosphate, Pi, in muscle tissues.

Their hypothesis is that an increase in the concentration of Pi prevents the release of calcium ions within muscle tissues.

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

Answer 13

1.   (Less/No) tropomyosin moved from binding site

OR Shape of tropomyosin not changed so binding site not exposed/available;

Ignore troponin. Reject active site only once.

2.   (Fewer/No) actinomyosin bridges formed;

Accept actin and myosin do not bind.

Reject active site only once.

3.   Myosin head does not move

OR Myosin does not pull actin (filaments)

OR (Less/No) ATP (hydrol)ase (activation);

Reject ATP synthase.

Do not penalise reference to calcium rather than calcium ions.

Credit all mark points even if context relates to what happens when calcium ions are present.