Exchange Surfaces

Question 1

Describe the basic structure of an alveolus

Answer 1

• Small air sac with a thin wall comprising one layer of squamous epithelial cells, elastic fibres and collagen fibres
• Each alveolus is surrounded by a capillary network

Question 2

What structures line the trachea and bronchi and what are their functions?

Answer 2

• Cartilage - supports the airway and prevents it collapsing
• Smooth muscle - contracts or relaxes to constrict or dilate the airway and change airflow
• Goblet cells - secrete mucus to trap dirt, dust or microorganisms
• Ciliated epithelial cells - lined with cilia to waft mucus away from the alveoli
• Bronchioles also contain smooth muscle, goblet cells and ciliated epithelial cells in their walls, but do not contain cartilage

Question 3

Which intercostal muscles contract during inspiration and expiration?

Answer 3

• Expiration - internal contract
• Inspiration - external contract

Question 4

Describe the structure and arrangement of fish gills

Answer 4

• Gills are composed of stacks of gill filaments
• These gill filaments have multiple gill lamallae to maximise surface area for gas exchange
• Gills are covered by an operculum flap

Question 5

What are tracheae and what is their role in insect gas exchange?

Answer 5

• Air filled tubes branching throughout the insects body
• Deliver oxygen directly into cells and remove carbon dioxide

Question 6

What adaptations make tracheoles good sites for gas exchange?

Answer 6

• Penetrate directly into tissues to reduce gas exchange distance
• Thin walls to reduce gas exchange distance
• Highly branched to maximise their surface area
• Not reinforced with chitin so gas exchange can occur
• Tracheal fluid at the end of them allows oxygen to dissolve to aid diffusion and reduces water loss

Question 7

What are some ventilation movements that some insects use when oxygen demands rises?

Answer 7

• More spiracles open
• Breathing rate increases
• Mechanical active ventilation - muscles around the tracheae contract/relax, squeezing tracheae to pump in/out of spiracles
• Enlarged collapsible tracheae - inflate or deflate to ventilate the tracheal system
• Vibration of thoracic muscles - pumps air to ventilate the tracheal system