DP Biology (last assessment 2024)

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Question 23M.3.HL.TZ2.23

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Date May 2023 Marks available [Maximum mark: 4] Reference code 23M.3.HL.TZ2.23
Level HL Paper 3 Time zone TZ2
Command term Describe, Outline Question number 23 Adapted from N/A
23.
[Maximum mark: 4]
23M.3.HL.TZ2.23

Acid conditions in the stomach favour some hydrolysis reactions and help to control pathogens in ingested food.

(a)

Describe the production of acid in the digestive system.

[2]

Markscheme
  1. controlled by nervous and hormonal mechanisms;
  2. hydrochloric acid is secreted;
  3. secreted by parietal cells/stomach wall/lining;
  4. achieved by a proton pump / H+-K+ ATPase;
  5. H+ from the cytoplasm exchanged for K+ in lumen;

Accept details to that effect, e.g. gastrin.

Examiners report

Many candidates could describe the production of acid in the stomach. Many didn't seem to understand its nervous and endocrine control (gastrin is produced by the G-cells in the stomach, not the hypothalamus as many wrote).

(b)

Outline the use of drugs to reduce the production of stomach acid.

[2]

Markscheme
  1. proton pump inhibitors (PPI) used;
  2. PPIs activated by acid;
  3. PPIs bind irreversibly to pump
    OR
    prevent stomach cells from pumping acid into stomach;
Examiners report

Most candidates knew that PPIs could reduce the production of acid in the stomach, but it was more difficult for many to outline their mechanism of action.