Question 19M.3.HL.TZ1.23
| Date | May 2019 | Marks available | [Maximum mark: 6] | Reference code | 19M.3.HL.TZ1.23 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain, Outline | Question number | 23 | Adapted from | N/A |
The diagram shows the bacterium Helicobacter pylori attacking the gastric mucosa of the stomach.
[Source: Reproduced from Gut, B A Hills, 34, 588–593, 1993 with permission from BMJ Publishing Group Ltd.]
Outline the possible consequences of a Helicobacter pylori infection of the stomach wall.
[2]
a. causes inflammation ✔
b. digestion of stomach lining by pepsin and HCl/gastric juice ✔
c. called «gastric» ulcer ✔
Student answers revealed much confusion regarding how the bacteria affects the stomach, and again the quality of the responses was affected by lack of precision. Few could explain what caused the digestion of the stomach lining, and the most common marking point achieved was for simply stating that the bacterium causes ulcers.
The bacterium secretes an enzyme that breaks down urea, resulting in an increase in pH. Outline how this would help the bacterium survive in the stomach.
[1]
neutralizes the acid the stomach secretes that kills bacteria ✔
While most students achieved this mark, many seem to think that “higher pH values” indicate greater acidity.
Explain hormonal control of gastric secretion.
[3]
a. release of gastric juices stimulated by gastrin ✔
b. gastrin stimulates secretion of gastric hydrochloric acid ✔
c. from the parietal cells «of the stomach» ✔
d. gastrin release stimulated by presence of polypeptides/amino acids in stomach ✔
e. gastrin stimulates release of pepsinogen by chief cells «of the stomach» ✔
f. drop in pH/excess acid/secretion of secretin/somatostatin inhibits gastrin secretion ✔
Of all the questions on this paper, this one seemed to encourage the most number of irrelevant statements. Students wrote about the role of the hypothalamus and the pituitary, pancreatic secretions and leptin almost as often as they outlined the role of gastrin. Even students who focused on gastric secretions often wrote more about control by the nervous system.