AQA · A-Level · Physical Education
Course version: 7582 · Version from Sept 2016
Respiratory system: Oxygen and carbon dioxide.
Oxygen and carbon dioxide are the two gases exchanged in the respiratory system.
Checked against the AQA 7582 specification (opens in a new tab) on .
- Point 8 of 17
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Oxygen and carbon dioxide are the two gases exchanged in the respiratory system. Oxygen is carried in blood mainly bound to haemoglobin in red blood cells, forming oxyhaemoglobin, with a small amount dissolved in plasma. Carbon dioxide is transported in three ways: dissolved in plasma, bound to haemoglobin as carbaminohaemoglobin, and as hydrogencarbonate ions after conversion in red blood cells. At the alveoli, oxygen loading and carbon dioxide unloading occur; at muscles, oxygen unloading and carbon dioxide loading occur. The partial pressure of each gas determines the direction of diffusion, and the difference between alveolar and blood partial pressures maintains exchange.
What earns the marks
- Oxygen is transported mainly as oxyhaemoglobin in red blood cells, with a small amount dissolved in plasma.
- Carbon dioxide is transported dissolved in plasma, bound to haemoglobin as carbaminohaemoglobin, and as hydrogencarbonate ions.
- At alveoli, oxygen loads onto haemoglobin and carbon dioxide is unloaded into alveolar air.
- At muscles, oxygen unloads from haemoglobin into muscle fibres and carbon dioxide loads into blood.
- Partial pressure gradients determine the direction of diffusion for each gas.
- The difference between alveolar and blood partial pressures maintains continuous exchange.
Common mistakes and how to put them right
Thinking all oxygen is dissolved in plasma.
Put it right: Most oxygen is carried bound to haemoglobin as oxyhaemoglobin.
Believing carbon dioxide is carried only as hydrogencarbonate.
Put it right: It is also dissolved in plasma and bound to haemoglobin as carbaminohaemoglobin.
Assuming oxygen and carbon dioxide always move in the same direction.
Put it right: Their directions reverse between alveoli and muscles.
Confusing partial pressure with total pressure.
Put it right: Partial pressure of each gas drives its own diffusion.
Exam tips
- Name the transport forms of oxygen and carbon dioxide precisely, including oxyhaemoglobin and hydrogencarbonate.
- Link each transport form to the site where loading or unloading occurs.
- Use partial pressure gradients to explain why each gas moves in a particular direction.
Try the lesson
The start of the Respiratory system: Oxygen and carbon dioxide. lesson, made from checked teaching notes for this specification point.
Have a go first
At the tissues, oxygen moves from the blood plasma into the muscle cells. Which process describes this movement of oxygen?
Listen
Oxygen and carbon dioxide are the two gases exchanged in the respiratory system. Oxygen is carried in blood mainly bound to haemoglobin in red blood cells, forming oxyhaemoglobin, with a small amount dissolved in plasma. Carbon dioxide is transported in three ways: dissolved in plasma, bound to haemoglobin as carbaminohaemoglobin, and as hydrogencarbonate ions after conversion in red blood cells. At the alveoli, oxygen loading and carbon dioxide unloading occur; at muscles, oxygen unloading and carbon dioxide loading occur. The partial pressure of each gas determines the direction of diffusion, and the difference between alveolar and blood partial pressures maintains exchange. A strong answer earns marks for these points. Oxygen is transported mainly as oxyhaemoglobin in red blood cells, with a small amount dissolved in plasma. Carbon dioxide is transported dissolved in plasma, bound to haemoglobin as carbaminohaemoglobin, and as hydrogencarbonate ions. At alveoli, oxygen loads onto haemoglobin and carbon dioxide is unloaded into alveolar air. At muscles, oxygen unloads from haemoglobin into muscle fibres and carbon dioxide loads into blood. A common slip: Thinking all oxygen is dissolved in plasma. Instead, most oxygen is carried bound to haemoglobin as oxyhaemoglobin. Exam tip: Name the transport forms of oxygen and carbon dioxide precisely, including oxyhaemoglobin and hydrogencarbonate.
Key words
Say what each word means before you turn the card.
Gas transport
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Haemoglobin binding
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Partial pressure gradients
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Alveolar and muscle exchange
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See every definition
- Gas transport
- Oxygen and carbon dioxide are the two gases exchanged in the respiratory system and carried in the blood in different forms.
- Haemoglobin binding
- Oxygen is carried mainly bound to haemoglobin in red blood cells, forming oxyhaemoglobin, and carbon dioxide is bound to haemoglobin as carbaminohaemoglobin.
- Partial pressure gradients
- The partial pressure of each gas determines the direction of diffusion, and the difference between alveolar and blood partial pressures maintains continuous exchange.
- Alveolar and muscle exchange
- At the alveoli, oxygen loading and carbon dioxide unloading occur; at muscles, oxygen unloading and carbon dioxide loading occur.
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