The diagram shows the results of an experiment investigating the effect of exercise intensity on ventilation rate (breathing rate) and tidal volume (volume of air per breath) in humans. Measurements were taken before exercise (Rest), during moderate exercise, and during heavy exercise.
[VISUALIZATION: Bar chart comparing Ventilation Rate (breaths/min) and Tidal Volume (L/breath) at Rest, Moderate Exercise, and Heavy Exercise. Rest: Rate=12, Volume=0.5. Moderate: Rate=25, Volume=1.5. Heavy: Rate=40, Volume=2.5. Error bars should be included, showing some variation but clear differences between conditions.]
(a) Calculate the total volume of air inhaled per minute (minute ventilation) during heavy exercise. Show your working. [2]
(b) Describe the changes observed in ventilation rate and tidal volume from rest to heavy exercise. [2]
(c) Explain the physiological mechanism that leads to the increase in ventilation rate during exercise. [3]
Question
(a) Calculate the total volume of air inhaled per minute (minute ventilation) during heavy exercise. Show your working. [2]
Hint
Hint
Hint
Minute ventilation is found by multiplying the ventilation rate (breaths per minute) by the tidal volume (litres per breath). Use the values for heavy exercise from the chart.
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100 L/min
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Question
(b) Describe the changes observed in ventilation rate and tidal volume from rest to heavy exercise. [2]
Hint
Hint
Hint
Look at the bar chart [VISUALIZATION] and compare the height of the bars for ‘Rest’ and ‘Heavy Exercise’ for both ventilation rate and tidal volume. Quote the values.
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Ventilation rate increases from 12 breaths/min at rest to 40 breaths/min during heavy exercise. Tidal volume increases from 0.5 L/breath at rest to 2.5 L/breath during heavy exercise.
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(c) Explain the physiological mechanism that leads to the increase in ventilation rate during exercise. [3]
Hint
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Consider the metabolic demands of exercise. How does the body detect changes related to increased metabolism (e.g., CO2 levels)? Which part of the brain controls breathing, and how does it respond?
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Increased muscle activity during exercise raises CO₂ production, leading to a decrease in blood pH. Chemoreceptors (in the medulla, aorta, and carotid arteries) detect these changes and send signals to the ventilation centre in the medulla oblongata. The medulla then sends increased nerve impulses to the diaphragm and intercostal muscles, causing them to contract more frequently and forcefully, thus increasing ventilation rate and depth (tidal volume).
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