How does the respiratory system get oxygen into the blood during exercise, and what are tidal volume and vital capacity?
The structure of the respiratory system, the mechanism of breathing, gas exchange at the alveoli, the lung volumes (tidal volume, vital capacity and minute ventilation), and aerobic and anaerobic respiration applied to physical activity.
A focused CCEA GCSE Physical Education answer on the respiratory system, covering its structure, the mechanism of breathing, gas exchange at the alveoli, lung volumes including tidal volume and vital capacity, and aerobic and anaerobic respiration in sport.
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What this dot point is asking
CCEA wants you to know the structure of the respiratory system, the mechanism of breathing, gas exchange at the alveoli, the lung volumes (tidal volume, vital capacity, minute ventilation), and aerobic and anaerobic respiration, applied to exercise. Lung volumes and the alveolar adaptations are common CCEA questions.
Structure and the mechanism of breathing
Breathing works by changing the volume and therefore the pressure inside the chest:
- Breathing in (inspiration): the intercostal muscles contract and pull the ribs up and out; the diaphragm contracts and flattens. Chest volume increases, pressure falls, so air flows in.
- Breathing out (expiration): the muscles relax; the ribs move down and in and the diaphragm domes up. Chest volume decreases, pressure rises, so air is pushed out.
Gas exchange at the alveoli
Alveoli are adapted for efficient gas exchange by a large surface area (millions of them), walls one cell thick (a short diffusion distance), a good blood supply of capillaries (keeping a steep concentration gradient) and moist surfaces (so gases dissolve and diffuse). These adaptations matter most during exercise, when oxygen demand is high.
Lung volumes
Aerobic and anaerobic respiration
Examples in context
Example 1. The marathon runner versus the sprinter. A marathon runner works mostly aerobically, breathing deeply and steadily so oxygen supply matches demand and energy is released efficiently over a long time. A 100 m sprinter works mostly anaerobically: the effort is too intense for oxygen supply to keep up, so energy is released without oxygen and lactic acid builds up, causing fatigue and the need to recover afterwards. CCEA likes you to match the type of respiration to the activity.
Example 2. Why we keep breathing hard after exercise. After hard exercise you keep breathing deeply and quickly for a while. This is repaying the oxygen debt: the extra oxygen is used to break down the lactic acid that built up during anaerobic work and to restore the body to its resting state. The fitter the performer, the faster this recovery, which connects the respiratory system to the long-term effects of training.
Try this
Q1. Name the tiny air sacs where gas exchange takes place. [1 mark]
- Cue. The alveoli.
Q2. State what happens to tidal volume and breathing rate during exercise. [2 marks]
- Cue. Both increase: breaths become deeper and more frequent.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 2022 Paper 14 marksExplain how the alveoli are adapted for efficient gas exchange during exercise.Show worked answer →
Four marks for four adaptations, each linked to faster diffusion.
There are millions of alveoli, giving a very large surface area for gases to diffuse across.
The alveolar walls are only one cell thick, so the diffusion distance for oxygen and carbon dioxide is very short.
The alveoli have a rich capillary blood supply, which keeps a steep concentration gradient by removing oxygen and bringing carbon dioxide.
The surfaces are moist, so gases dissolve before diffusing.
Markers reward large surface area, thin walls, good blood supply and moist surface, each linked to faster gas exchange, which matters more in exercise when oxygen demand is high.
CCEA 2021 Paper 13 marksDefine tidal volume and explain how it changes during exercise.Show worked answer →
One mark for the definition, two for the change and its purpose in exercise.
Tidal volume is the volume of air breathed in or out of the lungs in one normal breath.
During exercise the tidal volume increases, because each breath is deeper to move more air in and out.
This brings in more oxygen for aerobic respiration in the muscles and removes the extra carbon dioxide produced.
Markers reward tidal volume defined as the air per breath, and the increase explained as deeper breaths supplying more oxygen and removing more carbon dioxide.
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