Breathing
Overview
You have taken roughly twenty thousand breaths since this time yesterday and noticed almost none of them. Each one is a small piece of engineering: a set of muscles changes the shape of your chest, the pressure inside it drops below the pressure of the room, and air does the rest by moving from where there is more of it to where there is less. Nothing sucks the air in. It is pushed in, by the atmosphere.
This lesson takes that machinery apart. You will trace the path air follows from the trachea down to the alveoli, learn the exact sequence of muscle, volume and pressure that the specification wants for inhaling and exhaling, and see why a gas exchange surface the size of a badminton court is folded up inside your ribcage. By the end you should be able to label any diagram of the respiratory system, write either breathing sequence out in order without hesitating, and explain the movement of both gases across the alveolar wall in terms of one idea: a difference in concentration that the body works constantly to keep steep.
Objectives
- The respiratory (breathing) system takes air into and out of the body so that oxygen from the air can diffuse into the bloodstream and carbon dioxide can diffuse out of the bloodstream into the air. The lungs are in the upper part of the body (thorax), protected by the ribcage and separated from the lower part of the body (abdomen) by the diaphragm. Students should be able to recognise the following on a diagram of the respiratory system: ribs, intercostal muscles, diaphragm, lungs, trachea, bronchi, bronchioles, alveoli.
- To inhale: the intercostal muscles contract, pulling the ribcage upwards; at the same time the diaphragm muscles contract, causing the diaphragm to flatten; these two movements cause an increase in the volume of the thorax; the consequent decrease in pressure to below that of the air surrounding the body results in atmospheric air entering the lungs. To exhale: the intercostal muscles relax, allowing the rib cage to move downwards; at the same time the diaphragm muscles relax, allowing the diaphragm to resume its domed shape; these two movements cause a reduction in the volume of the thorax; the consequent increase in pressure results in air leaving the lungs.
- The alveoli provide a very large surface area, richly supplied with blood capillaries, so that gases can readily diffuse into and out of the blood.
Mind map
This topic is mapped out so you can see how the ideas connect.
Open the mind map in the app
Flashcards
Quick recall practice on the facts this topic is tested on.
Practise these cards in the app
Lesson Note
Complete Note Available on the Green Bridge App
Get the Green Bridge CBT app on your phone or computer for the complete IGCSE library: past papers, mark schemes, mind maps, flashcards and audio lessons.
Lesson Evaluation
Congratulations on completing the lesson on Breathing. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Which structure separates the thorax from the abdomen? A. The ribcage B. The diaphragm C. The trachea D. The bronchioles Answer: B
- Which of these happens when a person inhales? A. The diaphragm relaxes and becomes domed B. The volume of the thorax decreases C. The intercostal muscles contract and the ribcage moves upwards D. The pressure inside the thorax rises above atmospheric pressure Answer: C
- Approximately what percentage of exhaled air is carbon dioxide? A. 0.04% B. 4% C. 16% D. 21% Answer: B
- Which feature of the alveoli most increases the rate at which oxygen diffuses into the blood? A. Rings of cartilage that hold them open B. A large surface area with walls one cell thick and many capillaries C. A thick layer of muscle in their walls D. Cilia that sweep mucus away from them Answer: B
- In the lungs, carbon dioxide moves from the blood into the air inside an alveolus. Which statement explains this movement? A. Energy is used to pump carbon dioxide across the alveolus wall B. The concentration of carbon dioxide is higher in the blood than in the alveolus C. The wall of the alveolus is thick, which slows the gas down D. Breathing out increases the concentration of carbon dioxide in the alveolus Answer: B
Work through these questions in the app
Work through these questions in the app
Recommended Books
Further learning from open sources
-
Textbook section
Breathing
Describe how the structures of the lungs and thoracic cavity control the mechanics of breathing
"Biology: Breathing" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/biology/pages/39-3-breathing. Access for free at https://openstax.org/books/biology/pages/1-introduction
-
Textbook section
Systems of Gas Exchange
Describe the passage of air from the outside environment to the lungs
"Biology: Systems of Gas Exchange" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/biology/pages/39-1-systems-of-gas-exchange. Access for free at https://openstax.org/books/biology/pages/1-introduction
Published by other organisations under open licences, credited as they ask. Links open their websites.
Practice Mock Questions
Want to practice mock questions on Breathing? Download the Green Bridge CBT app to access mock questions and full practice assessments for this topic.
Download The App On Google Playstore
Everything you need to excel in your exams
