DP Biology (last assessment 2024)

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Question 23M.3.HL.TZ1.8

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Date May 2023 Marks available [Maximum mark: 6] Reference code 23M.3.HL.TZ1.8
Level HL Paper 3 Time zone TZ1
Command term Explain Question number 8 Adapted from N/A
8.
[Maximum mark: 6]
23M.3.HL.TZ1.8

Explain how breathing is controlled by the brain.

[6]

Markscheme
  1. breathing is an automatic process/can occur without conscious intervention/is involuntary/ autonomic;
  2. voluntary/conscious factors can override automatic functions (for a limited time);
  3. control of the breathing comes from the respiratory centre;
  4. (respiratory centre) located in the medulla of the brain;
  5. exercise results in higher CO2 levels in blood;
  6. breathing rate changes in response changes to blood pH/acidity/CO2 level;
  7. medulla contains chemoreceptors
    OR
    chemoreptors in aortic/carotid bodies send signals to medulla;
  8. respiratory centre/medulla sends nerve impulses to diaphragm/intercostal muscles;
  9. stimulates (the intercostal muscles/diaphragm) to control breathing rate/depth of inspiration/contraction;
Examiners report

Many were able to get two marks out of six available for indicting that breathing was an automatic process and that the control centre was in the medulla of the brain. Very little further understanding was shown by most candidates although those that seemed better prepared for the examination could score four marks.

Syllabus sections