AQA · A-Level · Physical Education
Course version: 7582 · Version from Sept 2016
Respiratory system: Carbon dioxide.
Carbon dioxide is a primary byproduct of aerobic respiration and acts as the main chemical stimulus for the control of ventilation.
Checked against the AQA 7582 specification (opens in a new tab) on .
- Point 12 of 17
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Carbon dioxide is a primary byproduct of aerobic respiration and acts as the main chemical stimulus for the control of ventilation. During exercise, working muscles produce more carbon dioxide, which dissolves in the blood plasma and lowers blood pH, increasing acidity. This change is detected by chemoreceptors located in the carotid arteries, aortic arch, and medulla oblongata. The chemoreceptors send nerve impulses to the respiratory control centre (RCC) in the brain. The RCC then sends somatic motor impulses via the phrenic nerve to the diaphragm and intercostal nerves to the intercostal muscles. This increases the rate and depth of breathing to expel the excess carbon dioxide and restore blood pH to normal resting levels.
What earns the marks
- Carbon dioxide is the main chemical stimulus for regulating pulmonary ventilation.
- Increased carbon dioxide levels during exercise lower blood pH, increasing blood acidity.
- Chemoreceptors detect this increase in carbon dioxide and decrease in pH.
- Chemoreceptors send impulses to the respiratory control centre, which sends somatic impulses via the phrenic and intercostal nerves to increase breathing rate and depth.
Common mistakes and how to put them right
Believing oxygen is the primary stimulus to breathe.
Put it right: Carbon dioxide levels and the resulting pH changes are the main chemical drivers for ventilation.
Stating that the autonomic nervous system directly innervates the diaphragm.
Put it right: The RCC sends somatic motor impulses via the phrenic and intercostal nerves.
Forgetting to mention blood pH.
Put it right: An increase in carbon dioxide directly lowers blood pH, which is what the chemoreceptors detect.
Exam tips
- Always link an increase in carbon dioxide to a decrease in blood pH when discussing chemical control of breathing.
- Name chemoreceptors as the specific sensory receptors that detect changes in carbon dioxide.
- Explain the full sequence: increased carbon dioxide lowers pH, stimulating chemoreceptors, which activate the RCC to send somatic impulses to respiratory muscles.
Try the lesson
The start of the Respiratory system: Carbon dioxide. lesson, made from checked teaching notes for this specification point.
Have a go first
During steady aerobic exercise, which waste gas is produced by working skeletal muscle and carried away in the blood?
Listen
Carbon dioxide is a primary byproduct of aerobic respiration and acts as the main chemical stimulus for the control of ventilation. During exercise, working muscles produce more carbon dioxide, which dissolves in the blood plasma and lowers blood pH, increasing acidity. This change is detected by chemoreceptors located in the carotid arteries, aortic arch, and medulla oblongata. The chemoreceptors send nerve impulses to the respiratory control centre (RCC) in the brain. The RCC then sends somatic motor impulses via the phrenic nerve to the diaphragm and intercostal nerves to the intercostal muscles. This increases the rate and depth of breathing to expel the excess carbon dioxide and restore blood pH to normal resting levels. A strong answer earns marks for these points. Carbon dioxide is the main chemical stimulus for regulating pulmonary ventilation. Increased carbon dioxide levels during exercise lower blood pH, increasing blood acidity. Chemoreceptors detect this increase in carbon dioxide and decrease in pH. Chemoreceptors send impulses to the respiratory control centre, which sends somatic impulses via the phrenic and intercostal nerves to increase breathing rate and depth. Exam tip: Always link an increase in carbon dioxide to a decrease in blood pH when discussing chemical control of breathing.
See it
Key words
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Carbon dioxide as a chemical stimulus
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Blood pH and acidity
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Chemoreceptors and sensory detection
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Regulation of ventilation during exercise
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See every definition
- Carbon dioxide as a chemical stimulus
- A primary byproduct of aerobic respiration that acts as the main chemical stimulus for the control of ventilation.
- Blood pH and acidity
- Carbon dioxide dissolving in the blood plasma lowers blood pH, increasing acidity.
- Chemoreceptors and sensory detection
- Receptors located in the carotid arteries, aortic arch, and medulla oblongata that detect changes in carbon dioxide and pH.
- Regulation of ventilation during exercise
- The respiratory control centre sends somatic motor impulses via the phrenic and intercostal nerves to increase the rate and depth of breathing.
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