(a) Fig. 9.1 is a diagram of a relaxed sarcomere in striated muscle. [Figure 9.1]

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2023). The mark or mark type is shown in brackets.

1. [2] (a)(i) P pointing to thin filament ;
2. [2] (a)(i) R pointing to thick filament;
3. [2] (a)(ii) A-band - stays the same ;
4. [2] (a)(ii) I-band - gets narrower ;
5. [4] (b)(i) any four from:
6. [4] (b)(i) 1 competes with, acetylcholine / neurotransmitter or acetylcholine cannot bind to receptors or blocks receptors;
7. [4] (b)(i) 2 Na+ channels do not open or no / fewer, sodium ions enter (muscle fibre);
8. [4] (b)(i) 3 so, no / less, depolarisation of sarcolemma ;
9. [4] (b)(i) 4 no / fewer, action potentials / impulses (spread across muscle fibre) ;
10. [4] (b)(i) 5 Ca2+ (voltage-gated) channels do not open in sarcoplasmic reticulum or no / fewer, Ca2+ ions released by sarcoplasmic reticulum ;
11. [4] (b)(i) 6 no / fewer, Ca2+ ions bind to troponin or no exposing of binding sites or no / fewer, cross bridges / AW ;
12. [2] (b)(ii) any two from:
13. [2] (b)(ii) 1 affects, rib muscles / intercostal muscles / diaphragm, so unable to breathe;
14. [2] (b)(ii) 2 affects cardiac muscle so, stops blood circulation / heart failure / attack;
15. [2] (b)(ii) 3 cannot move so unable to escape from predators;
16. [2] (b)(ii) 4 cannot eat so starves ;