| Date | May 2021 | Marks available | 1 | Reference code | 21M.1.SL.tz0.6 |
| Level | Standard Level | Paper | Paper 1 | Time zone | time zone 0 |
| Command term | Question number | 6 | Adapted from | N/A |
Question
What causes an increase in ventilation?
A. A decrease in carbon dioxide content in the blood
B. A decrease in hydrogen ions in the blood
C. A decrease in blood pH
D. A decrease in blood acidity
Markscheme
C
Examiners report
Common higher level question. High-difficulty question (25.85 % correctly answered). B was a very strong distractor with more candidates selecting B rather than the correct answer of C. B was accepted as an answer because in a hypoxic environment this can be correct. (Note: the wording has been amended for the published version.) Therefore the difficulty of this question changed to 85.95 % candidates correctly answered.
