1.1.d. The cardiovascular and respiratory systems - Structure and function of the respiratory system — OCR GCSE Physical Education
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1.1.d. The cardiovascular and respiratory systems - Structure and function of the respiratory system explained
1.1.d. The cardiovascular and respiratory systems - Structure and function of the respiratory system covers 4 specification points, including • mouth • nose • trachea • bronchi •… and • diaphragm • intercostals.
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Open a point below for its explanation and revision guidance.
understand the pathway of air through the respiratory system: • mouth • nose • trachea • bronchi • bronchiole • alveoli
Air enters the body through the mouth or the nose, passes down the trachea, divides into the two bronchi, then into progressively narrower bronchioles, and finally reaches the alveoli. The alveoli are tiny air sacs where gas exchange occurs: oxygen diffuses into the blood and carbon dioxide diffuses out. A reliable method is to trace the route in order and give the function of each stage, for example noting that the nose warms, moistens and filters air, while the trachea is supported by cartilage rings that keep it open. Learners should be able to place each structure in the correct sequence and explain why the alveoli are suited to exchange, using their large surface area and thin walls.
know the role of respiratory muscles in breathing: • diaphragm • intercostals
Breathing moves air in and out of the lungs because skeletal muscles change the volume of the thoracic cavity. The diaphragm is a dome-shaped sheet of muscle separating the thorax from the abdomen. When it contracts it flattens and moves downwards, increasing thoracic volume and lowering pressure so air is drawn in (inspiration). When it relaxes it domes upwards, reducing volume and pushing air out (expiration). The intercostal muscles sit between the ribs. On inspiration the external intercostals contract, lifting the rib cage up and outwards, which also enlarges the thorax. On expiration these muscles relax and the ribs move down and in. Together the diaphragm and intercostals create the pressure changes that drive ventilation; the diaphragm contributes most of the volume change at rest.
know the definitions of: • breathing rate • tidal volume • minute ventilation
These three terms describe ventilation and are linked by one relationship. Breathing rate is the number of breaths taken in a given time, usually expressed per minute; at rest a typical adult takes about 12 to 20 breaths per minute. Tidal volume is the volume of air moved into or out of the lungs in one normal breath at rest, typically around 0.5 dm³ (500 cm³) for an adult. Minute ventilation is the total volume of air breathed in one minute and is calculated as breathing rate multiplied by tidal volume. For example, 15 breaths per minute × 0.5 dm³ per breath = 7.5 dm³ per minute. During exercise both breathing rate and tidal volume rise, so minute ventilation increases to supply more oxygen and remove more carbon dioxide. Keep units consistent: if tidal volume is in dm³, minute ventilation is in dm³ per minute.
understand about alveoli as the site of gas exchange.
The alveoli are tiny air sacs clustered at the ends of the bronchioles in the lungs, and they are the site of gas exchange. Oxygen moves from the air inside each alveolus across the thin alveolar wall and the capillary wall into the blood, while carbon dioxide moves from the blood into the alveolus to be breathed out. This transfer happens by diffusion, from a higher concentration to a lower concentration. Their large total surface area, thin walls, rich blood supply and moist surface make exchange efficient. A useful method is to trace one oxygen molecule from inhaled air through an alveolus into a capillary, then trace carbon dioxide the opposite way.
Your focus
- List the structures of the respiratory pathway in the correct order.
- Describe the function of the nose, trachea, bronchi and bronchioles.
- Explain how the alveoli are adapted for gas exchange.
Show all 12 objectives
- Describe the action of the diaphragm during inspiration and expiration.
- Describe the action of the intercostal muscles during inspiration and expiration.
- Explain how diaphragm and intercostal action changes thoracic volume to move air into and out of the lungs.
- Define breathing rate, tidal volume and minute ventilation accurately.
- State and apply the relationship between breathing rate, tidal volume and minute ventilation.
- Calculate minute ventilation from given values using consistent units.
- Identify the alveoli as the site of gas exchange.
- Describe the diffusion of oxygen into the blood and carbon dioxide out of the blood.
- Explain how alveolar features support efficient gas exchange.
1.1.d. The cardiovascular and respiratory systems - Structure and function of the respiratory system exam tips
Marking Points
- Orders the pathway correctly as mouth or nose, trachea, bronchi, bronchioles and alveoli.
- States that the nose warms, moistens and filters incoming air.
- Explains that the trachea divides into two bronchi, which branch into bronchioles.
- Identifies the alveoli as the site of gas exchange between air and blood.
- Describes diffusion of oxygen into the blood and carbon dioxide out of the blood at the alveoli.
- Identifies the diaphragm as a dome-shaped muscle separating the thorax from the abdomen.
- States that contraction of the diaphragm flattens and lowers it, increasing thoracic volume during inspiration.
- States that relaxation of the diaphragm domes it upwards, reducing thoracic volume during expiration.
- Identifies the intercostal muscles as lying between the ribs.
- States that contraction of the external intercostals lifts the rib cage up and outwards during inspiration.
- States that relaxation of the intercostals moves the ribs down and inwards during expiration.
- Defines breathing rate as the number of breaths taken per unit time, usually per minute.
- Defines tidal volume as the volume of air moved into or out of the lungs in one normal breath.
- Defines minute ventilation as the total volume of air breathed in one minute.
- States the relationship minute ventilation = breathing rate × tidal volume.
- Applies the relationship correctly with consistent units, for example 15 breaths per minute × 0.5 dm³ = 7.5 dm³ per minute.
- Identifies the alveoli as the site of gas exchange in the lungs.
- States that oxygen diffuses from the alveolus into the blood.
- States that carbon dioxide diffuses from the blood into the alveolus.
- Links efficient exchange to features such as large surface area, thin walls and a rich blood supply.
Examiner Tips
- 💡Write the pathway as an ordered list so the sequence is unambiguous.
- 💡Add the function of each structure next to its name to gain explanation credit.
- 💡Use the term diffusion when describing gas exchange at the alveoli.
- 💡Link each muscle to the volume and pressure change it produces, not just to a movement.
- 💡Use the terms inspiration and expiration precisely and match each muscle action to the correct phase.
- 💡Remember that the diaphragm does most of the work at rest, so do not give the intercostals equal credit for resting ventilation.
- 💡Learn the equation minute ventilation = breathing rate × tidal volume and show the substitution in calculations.
- 💡Check units carefully and convert cm³ to dm³ by dividing by 1000 before multiplying.
- 💡Link increases in breathing rate and tidal volume during exercise to the rise in minute ventilation.
- 💡Read the question stem to check whether it asks for the site, the gases or the features of alveoli.
- 💡Use the word diffusion when explaining how gases move.
- 💡Keep the direction of each gas clear: oxygen in, carbon dioxide out.
Common Mistakes
- Places the bronchioles before the bronchi; correct this by remembering that bronchi branch into narrower bronchioles.
- Treats the trachea and oesophagus as the same tube; correct this by noting that the trachea carries air while the oesophagus carries food.
- Names the alveoli as a passage for air only; correct this by explaining that they are the site of gas exchange.
- Confuses the direction of diaphragm movement; remember that contraction flattens and lowers the diaphragm, not raises it.
- Claims the intercostals pull the ribs downwards on inspiration; correct this by stating that external intercostals lift the ribs up and outwards.
- Treats the lungs as the muscles that cause breathing; correct this by naming the diaphragm and intercostals as the muscles that change thoracic volume.
- Reverses inspiration and expiration; correct this by linking air entering the lungs to increased thoracic volume and lowered pressure.
- Confuses tidal volume with minute ventilation; correct this by stating that tidal volume is one breath while minute ventilation is the total for one minute.
- Adds breathing rate and tidal volume instead of multiplying them; correct this by using minute ventilation = breathing rate × tidal volume.
- Mixes units such as cm³ and dm³ in one calculation; correct this by converting so both quantities use the same unit before multiplying.
- Describes breathing rate as the depth of a breath; correct this by defining it as the number of breaths per minute.
- Names the bronchi or trachea as the site of gas exchange; correct this by naming the alveoli.
- Reverses the direction of gas movement; correct this by stating that oxygen enters the blood and carbon dioxide leaves it.
- Treats gas exchange as active transport or as breathing movements; correct this by describing diffusion down a concentration gradient.