CIE A Level Biology (9700) 2019-2021

Revision Notes

9.1.4 Recognising Structures

Recognising Structures in the Gas Exchange System

Trachea

Trachea Cross Section, downloadable AS & A Level Biology revision notes

Trachea cross-section

  • A tracheal cross-section shows the large lumen which air has to travel through
  • The innermost cells of the trachea are the ciliated epithelia with projections called cilia

 

Trachea Light Micrograph, downloadable AS & A Level Biology revision notes

Trachea – light micrograph

  • The cells of the ciliated epithelium are shown here – the cells are tightly packed and interspersed with goblet cells, which are shown in white

 

Trachea Electron Micrograph, downloadable AS & A Level Biology revision notes

Trachea – electron micrograph

  • The density of the cilia are shown in this electron micrograph
  • The cilia are essential for sweeping bacteria and dust-filled mucus away from the lungs and up the trachea into the back of the mouth
  • This mucus is then swallowed, with any pathogens hopefully destroyed by the acidic conditions in the stomach

Bronchi

Bronchi Cross Section, downloadable AS & A Level Biology revision notes

Bronchi cross-section

  • Bronchi are distinctive from the trachea because their lumen is narrower; 8.7mm instead of 18mm
  • However, like the trachea, they are lined by ciliated epithelium

Bronchioles

Bronchiole Photomicrograph, downloadable AS & A Level Biology revision notes

Bronchiole – photomicrograph

  • Bronchioles are approximately 1mm or less in diameter
  • Smooth muscle and cuboidal epithelium are found in their walls

Alveoli

Alveoli, downloadable AS & A Level Biology revision notes

Alveoli

 

Emphysema Alveoli, downloadable AS & A Level Biology revision notes

Emphysema alveoli

  • Alveoli have a sponge-like appearance under a microscope due to their air spaces.
  • They are surrounded by an extensive capillary network and are lined by squamous epithelium

Walls of the trachea & bronchus

Wall of Trachea, downloadable AS & A Level Biology revision notes

Walls of the trachea

  • The tracheal lumen is around 15 to 20 mm and is lined by ciliated epithelia
  • The tracheal wall is surrounded by strong and flexible cartilage which flexes during breathing
  • The smooth muscle of the trachea constricts and allows air to be expelled with more force

 

Walls of the Bronchus, downloadable AS & A Level Biology revision notes

Walls of the bronchus

  • Like the trachea, the bronchus is lined with ciliated epithelium
  • The cartilage hoops provide structural support to the bronchi and the gland ducts secrete mucus in the bronchial tubes

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Go to Top