A-LevelBiologyControl and coordination9700/43 · May/June 2017 · Q610 Marks

Describe how tropomyosin and myosin are each involved in the sliding filament model of muscle contraction.

(a)(i)tropomyosin[2]
(a)(ii)myosin[4]
(b)(i)Striated muscle is made up of many specialised muscle cells known as muscle fibres or myocytes. There are two different types of muscle fibre in striated muscle: * fast twitch muscle fibres that contract quickly, but rapidly fatigue (get tired) * slow twitch muscle fibres that contract slowly and continue to contract for a long time. Table 6.1 shows some features of fast twitch and slow twitch muscle fibres. Table 6.1 feature | fast twitch fibre | slow twitch fibre ---|---|--- respiration | mainly anaerobic | mainly aerobic glycogen concentration | high | low capillaries | few | many Use the information in Table 6.1 to suggest and explain one advantage of: the high glycogen concentration in fast twitch fibres[2]
(b)(ii)many capillaries supplying slow twitch fibres.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[2] max 2 of:
1 tropomyosin / it, covers / uncovers, myosin binding sites on actin ; R inhibits R active site
2 when calcium ions bind to troponin, tropomyosin / it, moves / changes shape;
3 allows myosin to, bind to actin / form cross-bridges ; ora
[4] max 4 of:
1 ATP hydrolysis / ATP → ADP + Pi ;
2 (causes myosin) head to, pivot / rotate / tilt / stand up ;
3 myosin / head, binds to actin / forms cross-bridges with actin ; R active site
4 ADP and Pi detach ;
5 (myosin) head, swings back / returns to previous position ;
6 actin is moved / power stroke occurs ;
7 (new) ATP binds ;
8 myosin / head, detaches from actin / cross-bridges break ;
A mps in any order apart from 1, 4 and 7 which must be linked to correct action
[2] max 2 of:
1 to, supply / provide, (enough / plenty of) glucose ;
2 for glycolysis ;
3 as little ATP is produced by anaerobic respiration;
4 as few capillaries are present (to supply glucose directly) ;
[2] max 2 of:
1 to, supply / provide, (enough / plenty of) oxygen ;
2 aerobic respiration / oxidative phosphorylation;
3 to remove, carbon dioxide / lactate ; A lactic acid
4 to, avoid fatigue or promote, stamina / endurance (for exercise / work);

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.