Gas Exchange in Fish and Insects

• What type of exoskeleton do all insects possess?

  Rigid exoskeleton with a waxy coating
• What are spiracles in insects?

  Openings in the exoskeleton for air flow
• What do tracheae lead to in the insect respiratory system?

  Narrower tubes known as tracheoles
• What keeps the tracheae open in insects?

  Rigid rings of chitin
• Where does gas exchange take place in insects?

  In the muscle fibres of the insect
• What fills the ends of the tracheoles?

  Tracheal fluid
• How do gases reach the cells for gas exchange in insects?

  They dissolve in tracheal fluid before diffusing
• Why is the large number of tracheoles beneficial for insects?

  It provides a large surface area for gas exchange
• What is the ventilation mechanism in insects when at rest?

  • Energy requirements are low
  • Diffusion alone supplies oxygen
  • Spiracles may close to reduce water loss
• How do active insects achieve a rapid supply of oxygen?

  By contracting and relaxing thorax and abdomen muscles
• What happens to tracheal fluid during insect flight?

  It is drawn into the respiring muscle
• Why is the removal of fluid from tracheoles important?

  It reduces diffusion distance to muscle cells
• How does oxygen dissolve in water compared to air?

  Oxygen dissolves less readily in water
• How much more oxygen is in a given volume of air than in water?

  30 times more oxygen in air
• What is the structure of fish gills in bony fish?

  Series of gills on each side of the head
• What are lamellae in fish gills?

  Rows of flattened cells covering capillaries
• What does the counter-current system in fish gills ensure?

  Maintains concentration gradient along capillaries
• Where is the water with the lowest oxygen concentration found in fish gills?

  Adjacent to the most deoxygenated blood
• What is the ventilation mechanism in fish?

  • Constantly pushes water over gills
  • Lowers floor of buccal cavity to increase volume
  • Water flows into buccal cavity due to pressure difference
  • Raises floor of buccal cavity to push water into gill cavity
  • Operculum opens to release water
• What happens when the fish opens its mouth?

  Volume in buccal cavity increases, pressure decreases
• What occurs when the fish closes its mouth?

  Pressure in buccal cavity increases
• What happens to the operculum during the ventilation cycle?

  It is forced open to release water
• What causes the operculum to shut?

  Floor of buccal cavity is lowered