IB Biology HL C3.1.15 Ventilation Rate Feedback Control Questions

IB Biology HL C3.1.15 links rising CO₂ and falling blood pH with chemoreceptor signals to the medulla. Practise explaining how respiratory muscles change ventilation.

Exam points

Explain how increased blood CO₂ or lower pH is detected by chemoreceptors and signalled to the medulla.
Trace how medullary signals alter diaphragm and intercostal muscle activity to change ventilation and remove CO₂.

[Maximum number: 8]

There is a relationship between form and function in the diversity of molecules and of systems.

Explain the causes of a decreased blood pH and its effects on the ventilation rate in humans.

a. increased (cellular) respiration can increase $\mathrm{CO}_{2}$ levels in blood

OR

anaerobic (cellular) respiration produces lactic acid;

b. due to exercise/lack of oxygen;

c. (aqueous) carbon dioxide reacts to form carbonic acid $/ \mathrm{H}^{+}$ ions (and $\mathrm{HCO}_{3}{ }^{-}$ ions) OR

increased $\mathrm{CO}_{2}$ levels in blood cause a decrease in pH / acidosis

OR

lactic acid in blood can release $\mathrm{H}^{+}$ ions / can cause a decrease in pH /acidosis;

d. in the presence of carbonic anhydrase (enzyme);

e. chemoreceptors detect levels of carbon dioxide (in the blood)

OR

chemoreceptors monitor (blood) $\mathrm{pH} / \mathrm{H}^{+}$ (in blood);

f. (chemoreceptors) found in aorta/carotid arteries;

g. (chemosensors/chemoreceptors) send information to respiratory centre in brain OR

to the medulla/brainstem;

h. (medulla) sends nervous impulses to the external intercostal muscles;

i. (medulla) sends nervous impulses to the diaphragm;

j. through intercostal/phrenic nerve;

k. increasing breathing/ventilation rate;

l. increasing volume of the lungs (during inhalation)/ increasing depth of breathing;

Marking guidance:

8 max

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IB Biology HL C3.1.15 Ventilation Rate Feedback Control Questions question 1