| Date | November 2009 | Marks available | 2 | Reference code | 09N.3.HL.TZ0.13 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Calculate | Question number | 13 | Adapted from | N/A |
Question
Helicobacter pylori is able to live inside the stomach wall of humans. This bacterium can cause inflammation of the stomach wall (gastritis). There may be a link between H. pylori and the development of stomach cancer.
The graph below shows the blood levels of antibodies resulting from H. pylori infection for a control group without stomach cancer and a group with stomach cancer. The solid lines show the median concentrations for the control group and the group with stomach cancer. Antibody concentrations above 10 μg ml–1 indicate that there has been infection with H. pylori.
47 % of the control group had been infected with H. pylori. Calculate the percentage of the group with stomach cancer that had been infected. Show your working.
Using all of the data, evaluate the hypothesis that H. pylori causes stomach cancer.
A study in gerbils indicated that infection with H. pylori leads to a decrease in the secretion of hydrochloric acid. Discuss the consequences of this finding for the digestion of proteins in the stomach in humans.
Markscheme
higher percentage of those with stomach cancer have H. pylori infection;
higher median of those with stomach cancer have H. pylori infection;
infection/high level antibodies does not mean that gastric cancer will always result / many infected did not develop gastric cancer;
not all of those with stomach cancer had H. pylori infection;
pepsinogen would not be broken down to pepsin;
pepsin would not work as well due to incorrect pH;
it is not known if humans would respond in the same way as gerbils;
Examiners report
Overall, the calculation of a percentage of the group with H. pylori was calculated correctly.
Many did state that a higher percentage of those with stomach cancer have H. pylori. Few then went onto to also discuss the median. Many did though suggest that from the data, a high level of antibodies does not mean that gastric cancer will always result.
Some did suggest that a reduction in HCl production would disrupt the digestion of proteins, but only a few gained marks by giving reasons why this may happen and relating this to enzymes and protein digestion.
