{"id":255649,"date":"2026-07-13T04:32:05","date_gmt":"2026-07-13T01:32:05","guid":{"rendered":"https:\/\/1kitap1.com\/en\/cambridge-igcsetm-biology-4th-edition-d-g-mackean\/"},"modified":"2026-07-13T04:32:05","modified_gmt":"2026-07-13T01:32:05","slug":"cambridge-igcsetm-biology-4th-edition-d-g-mackean","status":"publish","type":"post","link":"https:\/\/1kitap1.com\/en\/cambridge-igcsetm-biology-4th-edition-d-g-mackean\/","title":{"rendered":"Cambridge IGCSEtm Biology 4th Edition – D G Mackean"},"content":{"rendered":"
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It renews the oxygen supply in the lungs and removes the remaining carbon dioxide. Horseshoe-shaped hoops of cartilage are present in the trachea and bronchi to stop them collapsing when we breathe in. The lungs contain no muscle fibres and are made to expand and contract by movements of the ribs and diaphragm. The diaphragm is a sheet of muscle tissue that separates the thorax from the abdomen (see Figure 11.2). When relaxed, it is domed slightly upwards. The ribs are moved by the intercostal muscles. The external intercostals (Figure 11.11) contract to pull the ribs upwards and outwards.<\/p>\n

The internal intercostals contract to pull them downwards and inwards. Figure 11.12 shows the contraction of the external intercostales making the ribs move upwards. Inspiration The diaphragm muscles contract and pull the diaphragm down (Figure 11.13(a)). The internal intercostal muscles relax while the external intercostal muscles contract and pull the ribcage upwards and outwards (Figure 11.14(a)). \u25b2 Figure 11.11 Ribcage seen from left side, showing external intercostal muscles These two movements make the volume in the thorax bigger, so forcing the lungs to expand.<\/p>\n

The reduction in air pressure in the lungs results in air being pulled in through the nose and trachea. This movement of air into the lungs is known as ventilation. \u25b2 Figure 11.12 Model to show action of intercostal muscles Expiration The diaphragm muscles relax, allowing the diaphragm to return to its domed shape (Figure 11.13(b)). The external intercostal muscles relax while the internal intercostal muscles contract, pulling the ribs downwards to cause a forced expiration (Figure 11.14(b)). The lungs are elastic and shrink back to their relaxed volume, increasing the air pressure inside them.<\/p>\n

This results in air being forced out again. \u25b2 Figure 11.13 Diagrams of thorax to show mechanism of breathing \u25b2 Figure 11.14 Movement of ribcage during breathing A piece of apparatus called the bell-jar model (Figure 11.15) can be used to show the way in which movement of the diaphragm results in inspiration and expiration. The balloons start off deflated. When the handle attached to the rubber sheet is pulled down, the balloons inflate.<\/p>\n

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The Cambridge IGCSE\u2122 Biology series consists of a Student\u2019s Book, Boost eBook, Workbooks and Teacher\u2019s Guide with Boost Subscription. To explore the entire series, visit www.hoddereducation.com\/cambridge-igcse-science Cambridge IGCSE\u2122 Biology Teacher\u2019s Guide with Boost Subscription Created with teachers and students in schools across the globe, Boost is the next generation in digital learning for schools and colleges, bringing quality content and new technology together in one interactive website.<\/p>\n

The Teacher\u2019s Guide includes a print handbook and a subscription to Boost, where you will find a range of online resources to support your teaching. \u2022 Confidently deliver the revised syllabus: guidance on how to approach the syllabus from experienced authors, practical support to help you work scientifically and safely, as well as lesson plans based on the provided scheme of work. \u2022 Develop key concepts and skills: let students see how their skills are developing with a range of worksheets, formative knowledge tests and detailed answers to all the questions in the accompanying Student\u2019s Book, Workbook and Practical Skills Workbook.<\/p>\n

\u2022 Enhance learning: videos and animations on key concepts, mathematical skills and practicals plus audio of technical terms to support vocabulary flashcards. To purchase Cambridge IGCSE\u2122 Biology Teacher\u2019s Guide with Boost Subscription, visit www.hoddereducation.com\/cambridge-igcse-science 1kitap1.com\/en 1kitap1.com\/en Cambridge International copyright material in this publication is reproduced under licence and remains the intellectual property of Cambridge Assessment International Education. Cambridge Assessment International Education bears no responsibility for the example answers to questions taken from its past question papers which are contained in this publication.<\/p>\n

Exam-style questions (and sample answers) have been written by the authors. In examinations, the way marks are awarded may be different. References to assessment and\/or assessment preparation are the publisher\u2019s interpretation of the syllabus requirements and may not fully reflect the approach of Cambridge Assessment International Education. Third-party websites and resources referred to in this publication have not been endorsed by Cambridge Assessment International Education. We have carried out a health and safety check of this text and have attempted to identify all recognised hazards and suggest appropriate cautions.<\/p>\n<\/blockquote>\n

This is a short excerpt from the opening of “” by Unknown, quoted for review and introduction purposes. All rights belong to the copyright holders.<\/em><\/p>\n

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