Mini Physics
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Breathing

The breathing system, breathing and respiration, tests on exhaled air, choking and smoking.

  • SEC G1 Science 2027
  • 3 lessons
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Before you begin

Breathing moves air; respiration releases usable energy inside cells. The two are linked by gas exchange and transport.

Learning goals
  • Breathing and respiration
  • Respiratory parts and functions
  • Inhaled and exhaled air
  • Carbon-dioxide test
  • Water-vapour test
  • Choking
  • Smoking and passive smoking
Syllabus statements covered
  • describe the roles of breathing and respiration in keeping humans alive
  • identify the following parts of the respiratory system and state their functions: windpipe, bronchi, lungs, diaphragm and ribcage
  • explain the differences in the composition of inhaled and exhaled air
  • use simple tests for: — carbon dioxide (limewater test)
  • use simple tests for: — water vapour (cobalt chloride paper test) [knowledge of detailed procedures of tests is not required]
  • explain how choking affects breathing
  • state the effects of smoking and passive smoking on the respiratory system (e.g. bronchitis, lung cancer)

Lessons

Work through them in order.

  1. Breathing and respirationExplain how the diaphragm and ribcage draw air into the lungs, and how breathing differs from respiration.
  2. Compare inhaled and exhaled airCompare inhaled and exhaled air using limewater and cobalt chloride paper.
  3. Choking and smokingExplain how airway blockage affects breathing and how smoking and passive smoking raise respiratory disease risks.

Practise and check

Recommended nextBreathing topic check

Topic reference

Topic picture

How chest movement moves airTwo schematic views compare normal breathing at rest. Inhalation: ribs move up and out, the diaphragm contracts and flattens, lungs expand, and air enters down the windpipe. Exhalation: ribs move down and in, the diaphragm relaxes into a dome, lungs recoil, and air leaves up the windpipe. The labels connect movement to volume and pressure changes.Breathe in: inhalationAir entersWindpipeBronchiLungLungDiaphragmContracts and flattensRibcage moves up and outLungs expandPressure falls below outside air pressureBreathe out: exhalationAir leavesWindpipeBronchiLungLungDiaphragmRelaxes and becomes dome-shapedRibcage moves down and inLungs recoilPressure rises above outside air pressureBreathing moves air into and out of the lungs.Respiration releases usable energy from food inside cells.
Scroll diagram horizontally to read all labels.
Follow movement → lung volume → air pressure → airflow. Air moves from higher to lower pressure. The drawings show breathing at rest and are schematic, not to scale; they do not show cellular respiration.