Exchange surfaces

• Why do multicellular organisms require specialised gas exchange surfaces?

  Because their smaller surface area to volume ratio means the distance for gas exchange is larger.
• How is surface area to volume ratio calculated?

  Ratio = Surface area / Volume
• What are three features of an efficient gas exchange surface?

  • Large surface area (e.g., root hair cells)
  • Thin/short distance (e.g., alveoli)
  • Steep concentration gradient (maintained by blood supply or ventilation, e.g., gills)
• Describe the trachea and its function in the mammalian gaseous exchange system.

  The trachea is a wide tube supported by C-shaped cartilage, lined with ciliated epithelium cells, and carries air to the bronchi.
• What is the function of ciliated epithelium cells in the trachea?

  They move mucus towards the throat to prevent lung infections.
• Describe the bronchi and their function in the mammalian gaseous exchange system.

  The bronchi are supported by rings of cartilage, lined with ciliated epithelium cells, and allow passage of air into the bronchioles.
• How many bronchi are there in the mammalian gaseous exchange system?

  Two, one for each lung.
• Describe the bronchioles and their function in the mammalian gaseous exchange system.

  Bronchioles are narrower than bronchi, do not need cartilage, and allow passage of air into the alveoli.
• What is the primary structural difference between bronchi and bronchioles?

  Bronchioles do not have cartilage and are mostly made of smooth muscle and elastic fibers.
• Describe the alveoli and their function in the mammalian gaseous exchange system.

  Alveoli are mini air sacs lined with epithelium cells, where gas exchange occurs, with walls only one cell thick.
• How many alveoli are there in each lung?

  Approximately 300 million.
• Explain the process of inspiration in the thorax.

  External intercostal muscles contract, diaphragm contracts and flattens, increasing thorax volume and drawing air in.
• What happens to the thorax during expiration?

  The external intercostal muscles relax, diaphragm relaxes and domes upwards, decreasing thorax volume and pushing air out.
• How does a spirometer work?

  A spirometer measures lung volume by having a person breathe into an airtight chamber, leaving a trace on a graph.
• What is vital capacity?

  The maximum volume of air that can be taken in or expelled from the lungs in one breath.
• How can vital capacity be calculated from a spirometer graph?


  By finding the maximum amplitude on the graph.
• What is tidal volume?

  The volume of air we breathe in and out during each breath at rest.
• How can tidal volume be calculated from a spirometer graph?

  By finding the amplitude at rest on the graph.
• What is breathing rate?

  The number of breaths taken per minute.
• How can breathing rate be calculated from a spirometer graph?

  By counting the number of peaks in one minute on the graph.
• What are the two main features of a fish’s gas transport system?

  • Gills: located within the body, supported by arches with multiple projections of gill filaments.
  • Lamellae: at right angles to gill filaments, increasing surface area and facilitating countercurrent exchange.
• Explain the process of gas exchange in fish.

  Water flows over the lamellae, oxygen diffuses into the bloodstream, and carbon dioxide diffuses into the water.
• How does the countercurrent exchange system maximise oxygen absorption in fish?

  It maintains a steep concentration gradient, allowing 80% of available oxygen to be absorbed.
• What are the three main features of an insect’s gas transport system?

  • Spiracles: holes on the body’s surface for gas or water exchange.
  • Tracheae: large tubes extending through body tissues, supported by rings.
  • Tracheoles: smaller branches dividing off the tracheae.
• Explain the process of gas exchange in insects.

  Gases move in and out of the tracheae through spiracles, with oxygen diffusing into tissues and carbon dioxide diffusing out.