Author: Bethannie Freeman
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Q1.
(a)     Describe the roles of calcium ions and ATP in the contraction of a myofibril.
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(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. _________________________________________________________________
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2. _________________________________________________________________
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(2)
(Total 7 marks)
Q2.
(a)     A sarcomere is made up of different molecules.
Complete the table by naming the molecule that carries out the function described.
 
Function | Name
Attaches to Z line at the end of the sarcomere |
Breaks down ATP |
Covers binding site on actin in relaxed myofibril |
(3)
(b)     The diagram shows the arrangement of actin and myosin in a sarcomere.
 
One form of muscle disease is caused by a mutated allele of a gene. This leads to production of myosin molecules that are unable to bind to other myosin molecules.
If myosin molecules are unable to bind to other myosin molecules, this prevents muscle contraction.
Use the diagram and your knowledge of how muscles contract to suggest why.
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(3)
(Total 6 marks)
Q3.
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.
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(1)
 (d)     The image shows glycogen granules present in skeletal muscle.
Explain their role in skeletal muscle.
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(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.
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(3)
(Total 10 marks)

Mark schemes
Q1.
(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]
Q2.
(a)     
Function | Name
Attaches to Z line at the end of the sarcomere | 1. Actin;
Breaks down ATP | 2. ATPase / myosin (head);
Covers binding site on actin in relaxed myofibril | 3. Tropomyosin;
Accept water
Accept troponin
3
(b)     1.      Can’t form myosin / thick filaments;
Neutral: prevents actin and myosin sliding filament action
2.      Can’t pull / can’t move actin / slide actin past / (myosin) have to be joined / fixed to pull actin;
Accept: myosin can’t pull on each other
3.      Myosin moves / if attached doesn’t move;
4.      Can’t move actin towards each other / middle of sarcomere / between myosin / can’t shorten sarcomere / can’t pull Z lines together.
Accept: contract for shorten
3
[6]
Q3.
(a)     C = M line / M disc / myosin filament
D = mitochondrion
E = myofibril
3
(b)     Sarcomere
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]