mechanism of ventilation in fish and insects

Question 1

name and describe the two main features of a fish’s transport system

Answer 1

gills: located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles
lamellae: at right angles to the gill filaments, give an increased surface, blood and water flow across them in opposite directions (counter-current exchange system)

Question 2

explain the process of gas exchange in fish

Answer 2

• buccal cavity volume increased to enable water to flow in, reduced to increase pressure
• water is pumped over the lamellae by the operculum, oxygen diffuses into the bloodstream
• waste carbon dioxide diffuses into the water and flows back out of the gills

Question 3

how does the countercurrent exchange system maximise oxygen absorbed by the fish?

Answer 3

• maintains a steep concentration gradient, as water is always next to blood of a lower oxygen concentration
• keeps rate of diffusion constant and enables 80% of available oxygen to be absorbed

Question 4

name and describe the 3 main features of an insect’s gas transport system

Answer 4

spiracles: holes on the body’s surface which may be opened or closed by a valve for gas or water exchange
tracheae: large tubes extending through all body tissues, supported by rings to prevent collapse
tracheoles: smaller branches dividing off the tracheae

Question 5

explain the process of gas exchange in insects

Answer 5

• gases move in and out of the tracheae through spiracles
• a diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out
• contraction of muscles in the tracheae allows mass movement of air in and out