Author: Philip Colls
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Muscles booklet revision questions              NAME:
Q1. The image below shows a transmission electron micrograph of a longitudinal section of skeletal muscle.
 
(a)     Name structures C, D and E.
C _________________________________________________________________
D _________________________________________________________________
E _______________________________________________________________(3)
(b)     Give the name of the structure shown between points A and B.
_________________________________________________________________(1)
(c)     Calculate the actual distance between points A and B. Give your answer in micrometres (µm).
Answer = __________________ µm
(1)
(d)     The image shows glycogen granules present in skeletal muscle.
Explain their role in skeletal muscle.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(2)
(e)     During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction.
Suggest how.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(3)
(Total 10 marks)
Q2. The diagram shows two relaxed sarcomeres from skeletal muscle.
 
(a)     When the sarcomeres contract, what happens to the length of
(i)      the I-band
_________________________________________________________(1)
(ii)     the A-band?
____________________________________________________________(1)
(b)     The length of each sarcomere in the diagram is 2.2 μm. Use this information to calculate the magnification of the diagram. Show your working.

 
 
Magnification ____________________
(2)
(c)     People who have McArdle’s disease produce less ATP than healthy people. As a result, they are not able to maintain strong muscle contraction during exercise. Use your knowledge of the sliding filament theory to suggest why.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
____________________________________________________ (3) (Total 7 marks)
Q3. The diagram shows the stages in one cycle that results in movement of an actin filament in a muscle sarcomere.
 
(a)     Describe how stimulation of a muscle by a nerve impulse starts the cycle shown in the diagram.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(3)
(b)     Each cycle requires hydrolysis of one molecule of ATP and moves one actin filament 40  nm. During contraction of a muscle sarcomere, a single actin filament moves 0.6 µm. Calculate how many molecules of ATP are required to produce this movement.

 
Answer __________________________________    (2)
(c)     After death, cross bridges between actin and myosin remain firmly bound resulting in rigor mortis. Using information in the diagram, explain what causes the cross bridges to remain firmly bound.
___________________________________________________________________
___________________________________________________________________
__________________________________________________(2) (Total 7 marks)
Q4. (a)     Figure 1 shows part of a myofibril from skeletal muscle.
 
Figure 1
(i)      Describe two features, visible in the diagram, which show that the myofibril is contracted.
1. ____________________________________________________________
______________________________________________________________
2. ____________________________________________________________
____________________________________________________________(2)
(ii)     Explain the role of calcium ions and ATP in bringing about contraction of a muscle fibre.
Calcium ions ___________________________________________________
______________________________________________________________
ATP ___________________________________________________
____________________________________________________________(3)
(b)     Figure 2 shows the structure of a neuromuscular junction.  The vesicles contain acetylcholine.
 
Figure 2
(i)      An action potential is generated at the cell body of the motor neurone.
Explain how this action potential passes along the motor neurone to the neuromuscular junction.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
____________________________________________________________ (3)
(ii)     When the action potential arrives at the neuromuscular junction, it results in the secretion of acetylcholine into the synaptic cleft. Explain how.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
____________________________________________________________(3)
(c)     Between the ages of 20 and 50, 10% of total muscle mass is lost. Between the ages of 50 and 80, a further 40% of the original total muscle mass is lost. Most of the muscle lost consists of fast fibres.
(i)      Plot a graph on the grid below to show the percentage of muscle mass remaining between the ages of 20 and 80. Assume that the rate of muscle loss in each age range is constant.
 
(3)
(ii)     Explain why explosive exercises, such as sprinting and weightlifting, will be more affected by this muscle loss than aerobic exercises, such as jogging.
______________________________________________________________
______________________________________________________________
(1)	 (Total 15 marks)
Q5. The diagram shows part of a myofibril from a relaxed muscle fibre.
 
(a)     When the muscle fibre contracts, which of the A band, I band and H zone
(i)      remain unchanged in length,
____________________________________________________________(1)
(ii)     decrease in length?
____________________________________________________________(1)
(b)     Explain what caused the decrease in length in part (a)(ii).
___________________________________________________________________
_________________________________________________________________(2)
(c)     The whole muscle fibre is 30 mm long when relaxed. Each sarcomere is 2.25 µm long when contracted. Use the scale given on the diagram to calculate the length of the contracted muscle fibre in millimetres.
Length of contracted fibre = ____________________ mm    (2)
(d)     The table gives some properties of the two different types of muscle fibre found in skeletal muscle.
(i)      Complete the table by writing the words ‘high’ or ‘low’ for the remaining three properties of each type of muscle fibre.
 
| Type of muscle fibre
| Type 1 | Type 2
Speed of contraction | high | low
Force generated | high | low
Activity of the enzymes of glycolysis | high | low
Number of mitochondria | |
Activity of Krebs cycle enzymes | |
Rate of fatigue | |
(3)
(ii)     The myosin-ATPase of type 1 muscle fibres has a faster rate of reaction than that in type 2 fibres. Use your knowledge of the mechanism of muscle contraction to explain how this will help type 1 muscle fibres to contract faster than type 2.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
____________________________________________________________(4)
(iii)     The blood leaving an active muscle with a high percentage of type 1 muscle fibres contained a higher concentration of lactate than that leaving a muscle with a high percentage of type 2 muscle fibres. Explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
_____________________________________________(2)  (Total 15 marks)
Q6. (a)    Describe the part played by each of the following in myofibril contraction.
(i)      Tropomyosin
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
____________________________________________________________(2)
(ii)     Myosin
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
 (2)
(b)     The table shows features of fast and slow muscle fibres.
 
Feature | Fast muscle fibre | Slow muscle fibre
Type of respiration | Mainly anaerobic | Mainly aerobic
Glycogen | High concentration | Low concentration
Capillaries | Few | Many
Use information from the table to suggest and explain one advantage of:
(i)      the high glycogen content of fast muscle fibres
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii)     the number of capillaries supplying slow muscle fibres.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(Total 8 marks)
Q7.
(a)     What is the role of ATP in myofibril contraction?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(b)     Scientists investigated the effect of not being able to produce creatine on the force produced by muscle. They used mice with a mutation that made them not able to produce creatine.
The force produced when these mice gripped with their paws was compared with the force produced by normal mice that were able to produce creatine.
The graph shows the scientists’ results.
 
(i)	What was the percentage fall in the mean force produced by mice not able to produce creatine, compared with the normal mice? Show your working.

Answer ____________________ %
(2)
(ii)      Suggest an explanation for these results.
______________________________________________________________
______________________________________________________________
____________________________________________________________(2)
(c)     The mice that were not able to produce creatine were homozygous for a recessive allele of a gene. Mice that are heterozygous for this allele are able to produce forces similar to those of normal mice that are homozygous for the dominant allele of the same gene.
Explain why the heterozygous mice can produce forces similar to those of normal mice.
___________________________________________________________________
___________________________________________________________________
____________________________________________________ (2) (Total 8 marks)
Q8. Researchers investigated whether the blood supply to slow and fast muscle fibres in a muscle changes with age. They used diaphragms taken from hamsters (Mesocricetus auratus). The diaphragm is in constant use for breathing. They took diaphragms from groups of young, adult and old hamsters.
They removed the diaphragm from each animal and took a sample of muscle tissue.They examined it under an optical (light) microscope. For each sample they selected several fields of view at random. In each field of view, they then counted the number of capillaries associated with each type of muscle fibre.
This allowed the researchers to calculate the mean number of capillaries for each type of muscle fibre, for each age group.
The table below shows the researchers’ results which include standard deviation (SD).

Hamster
age group

Number of
hamsters in
group

Mean number of capillaries associated
with each type of muscle fibre

| | Slow fibres (± SD) | Fast fibres (± SD)

Young

9

3.4
(±0.8)

4.0
(±0.8)

Adult

10

4.7
(±0.2)

6.3
(±0.4)

Old

8

4.6
(±0.9)

6.8
(±0.6)

(a)     Give four precautions that the researchers took to make their calculations of mean number of capillaries per fibre reliable.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
3. _________________________________________________________________
___________________________________________________________________
4. _________________________________________________________________
___________________________________________________________________
(4)

(b)     The researchers examined the muscle of an animal in the old age group. They found one field of view containing only slow muscle fibres. They counted 69 capillaries in this field of view.
(i)      Use a calculation to estimate how many slow muscle fibres were visible in this field of view. Show your working.

 
Number of slow muscle fibres = ___________________            (2)
(ii)     The actual number of slow muscle fibres in the field of view was not the same as the number you calculated in question (i).
Give one reason why.
______________________________________________________________
______________________________________________________________
____________________________________________________________(1)
(c)     A student read the report of the researchers’ investigation. She thought that the investigation was unethical but that a conclusion could still be made.
(i)      Suggest why she thought the investigation was unethical.
______________________________________________________________
______________________________________________________________
____________________________________________________________(1)
(ii)     She concluded that age had a significant effect on the mean number of capillaries per fibre. Evaluate this conclusion.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
 (4) (Total 12 marks)
Q9. (a)     Describe the roles of calcium ions and ATP in the contraction of a myofibril.

(5)
(b)     ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
(2)
(Total 7 marks)
Q10.
It is believed that each person is born with a certain percentage of slow and fast muscle fibres in their skeletal muscles. Most people have about 50% slow fibres and 50% fast fibres.
A sports scientist wondered if these percentages could change over time depending on the type of sport in which a person was involved. He knew from previous investigations that:
•        the number of mitochondria within a fibre can change
•        the diameter of a fibre can change
•        the number of muscle fibres in a skeletal muscle remains constant over time.
He determined the mean percentages of slow and fast fibres in skeletal muscles of different types of athletes.
His results are shown in the graph below in the form in which he presented them.
 
(a)     (i)      In which type of athlete would the sports scientist expect to find muscle fibres with the highest number of mitochondria?
______________________________________________________________
(1)
(ii)     Explain the reason for your choice of athlete.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(b)     The leg muscles of long-distance cyclists are usually larger than the leg muscles of non-athletes.
Suggest why.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
[Extra space] _______________________________________________________
 (3)
(c)     A reader of the sports scientist’s results stated that ‘the results show that regular weightlifting changes your proportion of slow and fast skeletal muscle fibres.’
Do you agree with this statement? Explain your answer.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(Total 8 marks)
Q11. Figure 1 shows sections through relaxed and contracted myofibrils of a skeletal muscle. The transverse sections are diagrams. The longitudinal sections are electron micrographs.
Figure 1
 
(a)     (i)      The electron micrographs are magnified 40 000 times.
Calculate the length of  band X in micrometres.
Show your working.

Length of band X = ____________________ µm
(2)

(ii)     Explain the difference in appearance between transverse sections A and C in Figure 1.
______________________________________________________________
______________________________________________________________
(1)
(b)     Explain what leads to the differences in appearance between the relaxed myofibril and the contracted myofibril.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________ (4)
(c)     Duchenne muscular dystrophy (DMD) is a condition caused by the recessive allele of a sex-linked gene. A couple have a son with DMD. They want to know the probability that they could produce another child with DMD. They consulted a genetic counsellor who produced a diagram showing the inheritance of DMD in this family.
This is shown in Figure 2.
Figure 2
 
The couple who sought genetic counselling are persons 6 and 7.
(i)      Give the evidence to show that DMD is caused by a recessive allele.
______________________________________________________________
______________________________________________________________
(1)

(ii)     Give the numbers of two people in Figure 2 who are definitely carriers of muscular dystrophy.
____________________________________________________________(1)
(iii)     Complete the genetic diagram to find the probability that the next child of couple 6 and 7 will be a son with muscular dystrophy. Use the following symbols:
X^D   = normal X chromosome
X^d   = X chromosome carrying the allele for muscular dystrophy
Y     = normal Y chromosome
 
| 6 | 7
Parental phenotypes | Unaffected | Unaffected
Parental genotypes | _______ | _______
Gametes | _______ | _______

 
 
Offspring genotypes          __________________________________
Offspring phenotypes        __________________________________
Probability of having a son with DMD _________________________      (4)
(d)     DMD is caused by a deletion mutation in the gene for a muscle protein called dystrophin. A deletion is where part of the DNA sequence of a gene is lost. People in different families may inherit mutations in different regions of this gene.
Scientists isolated the dystrophin gene from DNA samples taken from children 10, 11 and 12. They cut the gene into fragments using an enzyme. The scientists then used two DNA probes to identify the presence or absence of two of these fragments, called F and G. This allowed them to find the number of copies of each fragment in the DNA of a single cell from each child.
The table shows their results.
 
Child | Number of copies of gene fragment per cell
| F | G
10 (unaffected girl) | 2 | 1
11 (unaffected girl) | 2 | 2
12 (boy with DMD) | 1 | 0
(i)      The number of copies of gene fragments F and G shows that person 12 has DMD.
Explain how.
______________________________________________________________
______________________________________________________________
(1)
(ii)     The number of copies of gene fragments F and G shows that person 12 is male.
Explain how.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(iii)     The genetic counsellor examined the scientists' results. He concluded that person 10 is a carrier of DMD but her sister, 11, is not.
Describe and explain the evidence for this in the table.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
 (3)
(e)     Person 12 took part in a trial of a new technique to help people with DMD.
Doctors took muscle cells from person 12’s father and grew them in tissue culture.
They suspended samples of the cultured cells in salt solution and injected them into a muscle in person 12’s left leg. They injected an equal volume of salt solution into the corresponding muscle in his right leg. Person 12 was given drugs to suppress his immune system throughout the trial.
Four weeks later, the doctors removed a muscle sample from near the injection site in each leg. They treated these samples with fluorescent antibodies. These antibodies were specific for the polypeptide coded for by gene fragment G of the dystrophin gene.

The results are shown in the table.

Location and
treatment

Percentage of muscle
fibres labelled with
antibody

Left leg - injected
with cultured cells
suspended in salt
solution

6.8

Right leg - injected
with salt solution

0.0

(i)      Why was it necessary to treat person 12 with drugs to suppress his immune system?
______________________________________________________________
____________________________________________________________(1)
(ii)     Explain why salt solution was injected into one leg and cultured cells suspended in salt solution into the other.
______________________________________________________________
____________________________________________________________(1)
(iii)     This technique is at an early stage in its development. The doctors suggested that further investigations need to be carried out to assess its usefulness for treating people with DMD. Explain why they made this suggestion.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________ (4) (Total 25 marks)

Mark schemes
Q1.
(a)     C = M line / M disc / myosin filament
D = mitochondrion
E = myofibril
3
(b)     Sarcomere
1
(c)     Answer in range 1.14–1.18
1
(d)     1.      As a store of glucose
Ignore provide energy
OR
To be hydrolysed to glucose;
2.      For respiration / to provide ATP;
2
(e)     1.      Low pH changes shape of calcium ion receptors
Do not accept tropomyosin does not move
2.      Fewer calcium ions bind to tropomyosin;
Accept troponin
3.      Fewer tropomyosin molecules move away;
4.      Fewer binding sites on actin revealed;
5.      Fewer cross-bridges can form
OR
Fewer myosin heads can bind
Must include idea of fewer at least once
3 max
[10]
Q2.
(a)     (i)     Decreases;
Accept any word that means a decrease e.g. shorter / narrower / smaller etc
1
(ii)     Nothing / stays the same length / does not change;
1
(b)     1.      Two marks for correct answer of 29545-30455;
Correct answer = 2 marks outright. Range allows for a 1mm error in measuring
2.      One mark for incorrect answers in which candidate clearly divides measured width by actual width;
Ignore rounding up
2
(c)     (Idea ATP is needed for:)
1.      Attachment / cross bridges between actin and myosin;
Accept the role of ADP in attachment
2.      ‘Power stroke’ / movement of myosin heads / pulling of actin;
Not just ‘filaments slide’ as given in the question stem
3.      Detachment of myosin heads;
4.      Myosin heads move back / to original position / ‘recovery stroke’
3 max
[7]
Q3.
(a)     calcium ions;
bind to / displace tropomysin; (allow troponin)
reveal binding site on actin;
myosin binds to exposed sites on actin / actomyosin formed / 
cross bridges form between actin and myosin;
activates ATPase;
3 max
(b)     distance single actin filament moves divided by distance moved
using 1 ATP;
15 ATP;
2
(c)     respiration stops / no ATP produced;
ATP required for separation of actin and myosin / cross bridges;
2
[7]
Q4.
(a)     (i)      H band not visible / reduced / little / no thick filament / myosin only region / ends of thin filaments / actin close together;
I band not visible / reduced / little / no thin filament / actin only region;
A band occupies nearly all sarcomere / thick filament / myosin close to Z line;
Large zone of thick-thin overlap;
max 2
(ii)     Calcium ions:
Bind to troponin;
Remove blocking action of tropomyosin / 
expose myosin binding sites;
ATP:
Allows myosin to detach from actin / to break cross bridge;
[allow attach and detach]
Releases energy to recock / swivel / activate myosin head / drive power stroke;
max 3
(b)     (i)      Depolarisation of axon membrane / influx of Na^+ establishes local
currents;
Change permeability to Na^+ / open Na^+  gates of adjoining region;
Adjoining region depolarises / influx of Na^+;
3
(ii)     Depolarisation of (presynaptic) membrane;
Ca^2+  channels open / increased permeability to Ca^2+ causing influx of Ca^2+ ;
Vesicles move towards / fuse with presynaptic membrane;
[If ions mentioned once assume candidate is referring to ions throughout; if no mention of ions penalise once only]
3
(c)     (i)      1.  Correct axes labelled, correct orientation, linear scale;
2.  Key points (100%, 90% and 50%) plotted correctly;
3.  Plots joined by straight lines;
[allow reasonable hand-drawn straight lines]
3
(ii)     Fast fibres used (in explosive exercise);
[allow reverse for slow fibres]
1
[15]
Q5.
(a)     (i)      A band;
1
(ii)     H zone and I band;
1
(b)     filaments in I / thin filaments / actin filaments slide in between myosin / 
thick filament; thin filaments enter H zone / meet in middle of A band / 
pull Z lines closer;
2 
(c)     correct answer:         22.5 mm ;;                                 = 2 marks
OR relaxed sarcomere length =  / = 3 μm ;           = 1 mark
2 max
(d)     (i)      In table:
 
low | high
low | high
high | low
(1 mark per row;;;)
3
(ii)     1        overall rate of contraction limited by rate of ATP-splitting;
2        ATPase splits ATP / hydrolyses ATP / converts ATP to ADP
(+ phosphate);
3        ATP-splitting provides energy for any TWO from myosin-actin 
interaction; myosin head movement / actin to move relative
to myosin; to ‘cock’ myosin head;
4 max
(iii)     lactate = product of anaerobic respiration;
type 1 has higher activity of glycolytic enzymes / has lower activity
of Krebs cycle enzymes / has fewer mitochondria;
2
[15]
Q6.
(a)     (i)      1.      Moves out of the way when calcium ions bind;
1. Accept shape change with Ca^2+
1. Don't accept just “calcium”
2.      Allowing myosin to bind (to actin) / crossbridge formation;
1. Accept presence of calcium ions leads to movement instead of binds
Accept references to troponin
2
(ii)     1.      Head (of myosin) binds to actin and moves / pulls / slides actin past;
Q
2.      (Myosin) detaches from actin and re-sets / moves further along (actin)
1. Accept myosin power stroke (to move actin)
1. Accept push
1. Accept crossbridges form instead of myosin head binds to actin
1. Must refer to myosin head or crossbridges
3.      This uses ATP;
2 max
(b)     (i)      1.      (Glycogen broken down) gives (lots of) glucose for glycolysis / anaerobic respiration;
1. Give if context of anaerobic respiration clear
2.      Glycolysis / anaerobic respiration not very efficient / only yields 2 ATP per glucose;
2. Accept anaerobic respiration is a quick source of ATP for exercise
2. Accept very little ATP
2
(ii)     1.      (Many capillaries) give high concentration / lots of oxygen / shorter diffusion pathway for oxygen / large surface area for oxygen exchange / diffusion / good glucose supply with little glycogen present;
2.      Allows high rate of / more aerobic respiration OR prevents build-up of lactic acid / (muscle) fatigue;
3. Accept idea of aerobic respiration during endurance events / long periods of exercise
2
[8]
Q7.
(a)     1.      (Reaction with ATP) breaks/allows binding of myosin to actin/ actinomyosin bridge;
2.      Provides energy to move myosin head;
1. Credit ‘breaks’ or ‘allows’ binding to actin (because cyclical)
2. Allow in context of ‘power stroke’ or ‘re-cocking’ (because cyclical)
2. Ignore contraction on its own
2
(b)     (i)      Any value between 68.5 and 69.49 (%);;
If get difference of 0.9 but calculation of percentage incorrect, then award 1 mark;
2
(ii)     (Mutant mice)
1.     Unable to make phosphocreatine/ less phosphate available to make/recycle ATP;
2.     So less energy/so less ATP available for contraction/fast muscle fibres;
1 and 2. Reject production/creation of energy once
2. Accept less energy for grip
2. Accept no energy/no ATP for contraction/fast muscle fibres
2
(c)     1.      (Heterozygous) have one dominant/normal allele (for creatine production);
2.      (This) leads to production of enough/normal amount of creatine;
1. Accept has one allele/one copy of the gene for/that is making creatine
2
[8]
Q8.
(a)     1.      Fields of view randomly chosen;
2.      Several fields of view;
3.      All same species (of animal / hamster);
Reject general statements related to sample size. All mark points relate directly to information provided in Resource A.
Accept ‘all (Mesocricetus) auratus’.
4.      Same muscle / organ used / only diaphragm used;
5.      Used at least 8 (animals) in each (age) group.
4 max
(b)     (i)      15
Correct answer = 2 marks.
Allow 1 mark for showing
69 ÷ 4.6
OR
answer of 10 / 10.1 (correct calculation using fast in error.)
2
(ii)     1.      (Calculation) used mean (number of capillaries);
2.      Variation in number of capillaries per fibre.
Note: maximum of 1 mark for this question.
Ignore reference to an anomaly or calculation errors.
1 max
(c)     (i)      (Removing diaphragm means) animals / hamsters are killed.
1
(ii)     1.      (Suggests) significant (difference) between young and adult;
MP1, MP2, MP4 and MP5 can include use of figures but check figures are used correctly.
2.      (Suggests) not significant (difference) between adult and old;
Statements related to ‘results being significant / not significant’ do not meet the marking points. It is the difference that is significant or not. However, only penalise this error once.
3.      For slow and fast fibres;
This MP can be given in the context of either MP1 or MP2 but only allow once. As well as this context there must be a reference to ‘both’ types of fibre.
4.      (Suggests) significant (difference) between young and old for fast (fibres)
OR
(Suggests) not significant (difference) between young and old for slow (fibres);
All aspects of either approach required to gain credit.
5.      (Suggests) significant (difference) where means ± SD do not overlap
OR
(Suggests) not significant (difference) where means ± SD overlap;
All aspects of either approach required to gain credit.
6.      Stats test is required (to establish whether significant or not).
4 max
[12]
Q9.
(a)     1.      Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
2.      (Calcium ions) cause movement of tropomyosin (on actin);
3.      (This movement causes) exposure of the binding sites on the 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 (from actin sites).
5 max
(b)     1.      Releases relatively small amount of energy / little energy lost as heat;
Key concept is that little danger of thermal death of cells
2.      Releases energy instantaneously;
Key concept is that energy is readily available
3.      Phosphorylates other compounds, making them more reactive;
4.      Can be rapidly re-synthesised;
5.      Is not lost from / does not leave cells.
2 max
[7]
Q10.
(a)     (i)      (Group) 5 / marathon runners.
Must only include this group and no other.
1
(ii)     1.      (5 / marathon runners) have highest percentage of slow
         fibres;
Maximum of 1 mark if the wrong fibres have been identified.
2.      (Slow fibres) use aerobic respiration / aerobic respiration occurs in mitochondria;
Either approach requires identification of aerobic respiration.
3.      (Slow fibres) best for endurance / long periods of exercise / to avoid fatigue.
2 max
(b)     1.      No (overall) change in number of fibres;
Reject any suggestion of an increase in number of fibres.
2.      Increase in diameter of fibres;
‘Size’ without qualification is insufficient.
3.      (Due to) training / exercise;
4.      (Long-distance) cyclists have more / higher percentage of slow fibres (than fast);
A comparison is required to meet this MP.
5.      Slow fibres of wider diameter than fast fibres;
6.      (Long-distance) cyclists have more mitochondria;
7.      (Long-distance) cyclists have more capillaries (in muscles).
Idea of ‘more’ (than non-athletes) is required to gain credit.
Accept converse (for non-athletes) in MP4, MP6 and MP7.
3 max
(c)     1.      Weightlifting favoured by / weightlifters have a high proportion of
         fast / low proportion of slow fibres
OR
Weightlifters have more fast / fewer slow fibres than non-athletes;
But (cannot tell because):
Reward for general statement or comparison with non-athletes.
For ‘proportion’, accept percentage (or idea of a ratio).
2.      Do not know what ‘weightlifters’ (tested) were born with / had before started weightlifting / training
OR
Don’t know if there has been a change (in proportion due to weightlifting / training);
3.      No information about age / gender / number of weightlifters (in
         sample).
For this MP, accept another relevant factor that might affect ‘weightlifter’ e.g. weights lifted, sex, diet, ethnicity, country of birth.
Ignore general statements about ‘other factors’.
2 max
[8]
Q11.
(a)     Correct answer: 1.25;
Ignore working
OR    (if wrong answer)
 / = 1 mark

125 but wrong order of magnitude = 1 mark
2
(ii)     C has myosin / thick (and actin / thin) filaments;
OR
A has only actin / thin (/ no myosin / no thick) filaments;
1 max
(b)     When contracted:
Thick & thin filaments/myosin & actin overlap more;
Interaction between myosin heads & actin / cross-links form;
Movement of myosin head;
Thin filaments / actin moved along thick filaments / myosin;
Movement of thin filaments / actin pulls Z-lines closer together;
Displacement of tropomyosin to allow interaction;
Role of Ca^2+;
Role of ATP;
Allow ref. to ‘sliding filament mechanism’ /
described if no other marks awarded
4 max
(c)     (i)      8 has DMD but 3 and 4 do not / 12 has DMD but 6 and 7
do not / neither parent has the condition but their child has;
Allow parents 3 and 4 give 8, parents 6 and 7 give 12
1
(ii)     4 AND 7;
1
(iii)     Parental genotypes:  6 = X^DY AND 7 = X^DX^d
AND
Gametes correct for candidate’s P genotypes ‒ e.g.
X^D and Y + X^D and  X^d;
Offspring genotypes correctly derived from gametes e.g.
X^DX^D + X^DX^d + X^DY + X^dY;
Male offspring with MD correctly identified: X^dY;
Probability = 0.25 / correct for candidates offsprings genotypes;
Accept ¼ / 1 in 4 / 1:3 / 25%
NOT ‘3:1’ / ‘1:4’
4
(d)     (i)      No gene fragment G;
1
(ii)     Only one copy of gene fragment F;
Male has only one X-chromosome / is XY
(c.f. female has two / is XX);
2
(iii)     10 has only one copy of gene fragment G;
10 has only one normal X-chromosome / has one abnormal /
has only one normal allele / has one X^d / is X^DX^d / is heterozygous;
11 has two normal X-chromosomes / has 2 normal alleles /
is X^DX^D / has not got X^d / has 2 copies of (F and) G;
3
(e)     (i)      To prevent rejection / prevent antibody production vs. injected cells /
injected cells have (foreign) antigen (on surface);
1
(ii)     Shows effect of cells / not just effect of injection / not just effect of
salt solution;
1
(iii)     Only one person tested so far ‒ need more to see if similar results /
need more to see if reliable;
Need to assess if new (dystrophin positive) muscle fibres are
functional / if muscle becomes functional;
Can’t tell how widespread effect is in the muscle / sample taken
near injection site;
Need to test for harmful side effects;
Need to test if successful for other mutations of dystrophin gene;
Need to assess permanence / longevity of result/insufficient time
allowed in investigation;
(In this patient) only small response / %;
Further sensible suggestion;
4 max
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