How does the body get oxygen in and carbon dioxide out, and how does breathing change during exercise?
The structure and function of the respiratory system, the mechanics of breathing, gaseous exchange at the alveoli, lung volumes (tidal volume, vital capacity), and the respiratory response to exercise.
A focused answer to OCR GCSE PE Component 01 on the respiratory system: the pathway of air, the mechanics of breathing (the diaphragm and intercostal muscles), gaseous exchange at the alveoli, lung volumes including tidal volume and vital capacity, and the response to exercise.
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What this dot point is asking
OCR wants you to describe the pathway of air and the structure of the respiratory system, explain the mechanics of breathing, describe gaseous exchange at the alveoli, define the key lung volumes, and describe how breathing responds to exercise.
The pathway of air and structure
The mechanics of breathing
During hard exercise, expiration becomes active too: the internal intercostal muscles and abdominal muscles contract to push more air out quickly, so breathing is both deeper and faster.
Gaseous exchange at the alveoli
At the alveoli, gases move by diffusion down their concentration gradients. Oxygen is at a high concentration in the freshly breathed-in air, so it diffuses from the alveoli into the blood in the surrounding capillaries. Carbon dioxide is at a high concentration in the blood returning from the muscles, so it diffuses from the blood into the alveoli to be breathed out.
Lung volumes
During exercise, tidal volume increases (deeper breaths) and breathing rate increases (more breaths per minute), so the total amount of air moved per minute (minute ventilation) rises sharply to meet the demand for oxygen.
The respiratory response to exercise
The short-term response is faster, deeper breathing (higher breathing rate and tidal volume). The long-term effect of endurance training is stronger respiratory muscles, a larger vital capacity and more efficient gaseous exchange, all covered in the effects of exercise topic. Together with the cardiovascular response, this delivers the oxygen the muscles need to keep working aerobically.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20184 marksDescribe how gaseous exchange takes place at the alveoli and explain two features of the alveoli that make exchange efficient.Show worked answer →
A Component 01 item testing the exchange process and the adaptations of the alveoli.
For the process: at the alveoli, oxygen diffuses from the air in the alveoli (high concentration) into the blood in the surrounding capillaries (low concentration), and carbon dioxide diffuses the other way, from the blood into the alveoli to be breathed out. Exchange happens by diffusion, down the concentration gradient.
For two features (any two): a large surface area (millions of alveoli) gives more room for diffusion; thin walls (one cell thick) give a short diffusion distance; a rich capillary network keeps the concentration gradient steep; the walls are moist so gases dissolve and diffuse easily.
Markers reward the correct direction of diffusion for each gas plus two valid features linked to faster exchange.
OCR 20213 marksDefine tidal volume and explain how and why it changes when a performer begins to exercise.Show worked answer →
A 3-mark definition-and-application item on lung volumes.
Tidal volume is the volume of air breathed in or out per breath. At rest it is around half a litre.
During exercise, tidal volume increases because the muscles need more oxygen and produce more carbon dioxide. The performer breathes more deeply, taking in a larger volume per breath. Breathing rate (the number of breaths per minute) also increases.
Markers want the definition, the direction of change (increase), and the reason (to take in more oxygen and remove more carbon dioxide for the working muscles).
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Sources & how we know this
- OCR GCSE (9-1) Physical Education J587 specification — OCR (2016)