3.1.6 Gas Exchange in Fish & Insects

Question 1

Insect airways

Answer 1

• Spiracles
• Trachea
• Tracheoles (with rigid chitin rings keeping it open)
• Tracheoles run into muscle fibres where gas exchange occurs

Ventilate by :
- When flying
- Need more rapid intake of oxygen
- So close spiracles
- Abdomen muscles create pumping movement for ventilation
- During flight fluid at end of tracheoles is drawn into respiring muscles so gas diffuses through quicker

• One main blood vessel, dorsal vessel. Tubular heart in abdomen pumps haemolymph (blood)
• Surrounds organs and reenters heart via ostia
• Less efficietn but opxygen isdeliver

Question 2

Fish

Answer 2

• Gills
• 2 Filament stacks attached to gill arch
• With rows of lamellae
• Capillaries
• High SA
• Counter current flow
• Concentration gradient maintained across whole capillary

Mechanism :
- Fish opens mouth
- Floor of buccal cavity is lowered
- Volume of buccal cavity increases
- Pressure decreases
- Water flows into buccal cavity
- Fish closes its mouth
- Raises floor
- Increases pressure
- Operculum forced open
- Water flows from buccal cavity to gill cavity
- Operculum is pulled shut when floor lowered at next cycle
- Oxygenated water passes through gills