| Date | November 2012 | Marks available | 2 | Reference code | 12N.3.HL.TZ0.13 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Compare | Question number | 13 | Adapted from | N/A |
Question
Researchers explored the effects of roadside traffic exposure in London on people with asthma. Each participant walked for two hours through Hyde Park, a large traffic-free park, and on a separate occasion along Oxford Street, where diesel-powered buses and taxicabs are permitted. The researchers measured the pH of the participants’ exhaled breath two hours before each walk and three hours and six hours after the start of each walk. The level of an inflammation indicator, myeloperoxidase, was also measured the day after the experiment.
Calculate the percentage increase of myeloperoxidase between Hyde Park and Oxford Street for participants.
Compare the changes in exhaled breath pH caused by walking through Hyde Park and along Oxford Street.
Explain the changes in exhaled breath pH caused by walking along Oxford Street in people with asthma.
Markscheme
625 % (percentage required) (accept answers in the range of 600 % to 650 %)
pH rises in Hyde Park and falls along Oxford Street;
back to pre-walk level in six hours in Hype Park but not along Oxford Street;
asthma (attack) constricts bronchioles (while walking);
exercise/walking increases cell respiration producing more CO2;
lower ventilation causes CO2 build-up thus lower pH;
CO2/pollutants in the air could be causing/triggering acidification;
inflammation (by-products) lower pH;
Examiners report
Many candidates calculated the correct percentage increase, but also many did not know how to carry out the calculation.
Most candidates could state that one pH increased while the other decreased, but found it more difficult to state that it returned to the original value only in Hyde Park and to explain these changes.
Most explanations related to CO2 triggering acidification.
