| Date | November 2012 | Marks available | 1 | Reference code | 12N.1.HL.TZ0.38 |
| Level | Higher level | Paper | Paper 1 | Time zone | TZ0 |
| Command term | Question number | 38 | Adapted from | N/A |
Question
During muscle contraction, what is the role of calcium ions ( Ca2+) which are released from the sarcoplasmic reticulum?
A. To cause ATP hydrolysis on myosin filaments
B. To bind to both actin and myosin filaments forming a cross-bridge
C. To cause the cross-bridge to detach itself and start a new cycle
D. To cause binding sites on the actin filaments to be uncovered
Markscheme
D
Examiners report
This was another question with a very high discrimination index and a relatively low percentage of candidates answering correctly. More candidates than expected thought that calcium ions bind to actin and myosin filaments forming a cross-bridge. Although the candidates are not expected to know the roles of troponin and tropomyosin, they should understand that calcium ions cause the binding site for myosin heads to be uncovered on actin filaments.
