| Date | May 2013 | Marks available | 2 | Reference code | 13M.3.SL.TZ2.5 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Analyse | Question number | 5 | Adapted from | N/A |
Question
Analyse the electron micrograph for the state of contraction of the muscle fibre.
Outline ATP production in muscle fibres during intense exercise.
Explain the role of ATP in muscle contraction.
Markscheme
a. muscle fibre is (partially) contracted;
b. thick and thin filaments show considerable overlapping;
c. narrow/reduced light bands between Z lines / OWTTE;
a. for 8–10 seconds creatine phosphate regenerates ATP;
b. anaerobic respiration produces ATP until lactate too high/for about 2 minutes/ 800 m of running;
a. ATP breaks cross-bridges (between myosin and actin);
b. ATP resets/activates/changes position of/cocks myosin heads;
c. ATP provides energy to move actin/causes sliding of filaments;
Examiners report
In a, the better candidates were able to state that the fibre was (partially) contracted as there was a narrow/reduced light band between the Z lines.
b was not well answered, with few considering the duration of ATP regeneration by creatine phosphate or the time taken to build up lactic acid.
Better candidates could explain the role of ATP in muscle contraction.
