| Date | May 2013 | Marks available | 1 | Reference code | 13M.1.SL.TZ1.28 |
| Level | Standard level | Paper | Paper 1 | Time zone | Time zone 1 |
| Command term | Question number | 28 | Adapted from | N/A |
Question
What changes occur in the thorax of a mammal when the external intercostal muscles and diaphragm muscles contract?
A. Pressure increases and volume decreases.
B. Pressure and volume both increase.
C. Pressure and volume both decrease.
D. Pressure decreases and volume increases.
Markscheme
D
Examiners report
Question 28 was another one in which there was criticism of the vocabulary used. In this case it was felt that the word chest should have been used instead of thorax. It is true that only one third of candidates chose the correct answer to this question, but the discrimination index was excellent showing that many of the stronger candidates had been successful. It was possible to deduce that the thorax must be equivalent to the chest if it was known that contraction of external intercostal muscles and the diaphragm cause inspiration. The answer to the question could then be deduced, that the pressure decreases and the volume increases. Many candidates thought that contraction of these muscles caused the opposite; an increase in pressure and decrease in volume.
