How do we breathe, how do gases exchange in the lungs, and what is respiration?
The structure of the human respiratory system, the mechanism of breathing in and out, gas exchange in the alveoli and their adaptations, the difference between breathing and respiration, and aerobic and anaerobic respiration.
A focused CCEA GCSE Double Award Science (Biology Unit B1) answer on breathing and respiration, covering the respiratory system, the mechanism of breathing, gas exchange in the alveoli, the difference between breathing and respiration, and aerobic and anaerobic respiration with their equations.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
CCEA Double Award wants the parts of the respiratory system, how breathing in and out works, how gas exchange happens in the alveoli, the difference between breathing and respiration, and the equations for aerobic and anaerobic respiration. Keep "breathing" (the movement of air) and "respiration" (the release of energy in cells) clearly separate.
The respiratory system
Air enters through the nose or mouth, passes down the trachea, which branches into two bronchi, then into smaller bronchioles, ending in tiny air sacs called alveoli. The trachea is held open by rings of cartilage. The lungs sit in the chest, protected by the ribs and separated from the abdomen by the diaphragm.
The mechanism of breathing
The key idea is that muscles change the volume of the chest, which changes the pressure, and air always moves from high to low pressure.
Gas exchange in the alveoli
The alveoli are the site of gas exchange. Oxygen diffuses from the air in the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli to be breathed out. They are adapted for fast diffusion:
- A large total surface area (millions of alveoli).
- Walls one cell thick, so a short diffusion distance.
- A rich blood supply from surrounding capillaries, keeping a steep concentration gradient.
- A moist lining, so gases dissolve before diffusing.
Breathing versus respiration
Aerobic and anaerobic respiration
Aerobic respiration uses oxygen and happens mainly in the mitochondria, releasing a lot of energy. Anaerobic respiration happens when oxygen is short, such as during hard exercise; in muscle it produces lactic acid and far less energy, which is why it cannot continue for long.
Examples in context
Example 1. Why smokers get short of breath. Smoking damages the alveoli, reducing the surface area for gas exchange, and tar coats the airways. Less oxygen reaches the blood, so the smoker tires quickly and becomes breathless during exercise. This links the alveolar adaptations to health.
Example 2. Yeast and anaerobic respiration. In yeast, anaerobic respiration produces ethanol and carbon dioxide rather than lactic acid. This is used in brewing and bread-making, showing that anaerobic respiration differs between organisms.
Try this
Q1. State one way an alveolus is adapted for gas exchange. [1 mark]
- Cue. Large surface area (or thin walls, or rich blood supply).
Q2. What is produced when muscle cells respire anaerobically? [1 mark]
- Cue. Lactic acid.
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-style4 marksDescribe how an alveolus is adapted for efficient gas exchange.Show worked answer →
Pick adaptations and link each to its job for four marks.
Alveoli give a very large total surface area for diffusion.
Their walls are one cell thick, so the diffusion distance is short.
They have a rich blood supply from surrounding capillaries, which keeps a steep concentration gradient.
They are moist, so gases dissolve before diffusing. Markers reward each adaptation tied to faster diffusion.
CCEA-style3 marksGive the word equation for aerobic respiration and state where in the cell it mainly occurs.Show worked answer →
Equation for two marks, location for one.
Glucose + oxygen gives carbon dioxide + water (and releases energy).
It mainly takes place in the mitochondria of the cell.
Markers want the correct reactants and products and the mitochondria named.
Related dot points
- The components of the blood and their functions, the structure of the heart with its chambers and valves, the double circulatory system, the structure and adaptations of arteries, veins and capillaries, and the effect of lifestyle on heart health.
A focused CCEA GCSE Double Award Science (Biology Unit B2) answer on the circulatory system, covering the components of blood, the structure of the heart and its valves, the double circulation, the adaptations of arteries, veins and capillaries, and lifestyle effects on heart health.
- Enzymes as biological catalysts, the lock and key model and the active site, how temperature and pH affect enzyme activity including denaturing, the organs of the digestive system, the enzymes amylase, protease and lipase, the role of bile, and absorption in the villi.
A focused CCEA GCSE Double Award Science (Biology Unit B1) answer on enzymes and digestion, covering enzymes as biological catalysts, the lock and key model, the effects of temperature and pH, the digestive organs, the enzymes amylase, protease and lipase, bile, and absorption in the villi.
- The components of a balanced diet and their sources and functions, the consequences of an unbalanced diet, and the chemical food tests for starch, reducing sugar, protein and fat.
A focused CCEA GCSE Double Award Science (Biology Unit B1) answer on nutrition, covering the components of a balanced diet and their functions, the effects of an unbalanced diet, and the food tests for starch, reducing sugar, protein and fat with their colour changes.
- Animal and plant cell structures and their functions, examples of specialised cells and their adaptations, the levels of organisation from cell to organism, and using a light microscope including magnification calculations.
A focused CCEA GCSE Double Award Science (Biology Unit B1) answer on cell structure, covering the parts of animal and plant cells and their functions, specialised cells and their adaptations, levels of organisation, and using a light microscope with magnification calculations.
- The central nervous system, sensory, relay and motor neurones, the reflex arc as a fast automatic response, the structure and function of the eye, and how the eye focuses light and adjusts to light intensity.
A focused CCEA GCSE Double Award Science (Biology Unit B1) answer on coordination, covering the central nervous system, sensory, relay and motor neurones, the reflex arc, the structure of the eye, and how the eye focuses and adjusts to light intensity.
Sources & how we know this
- CCEA GCSE Science Double Award specification — CCEA (2017)