fish

Question 1

the gills

Answer 1

• make up the gaseous exchange surface of the gills.
• they take oxygen from the water and remove co2 into the water
• they have a rich blood supply to maintain concentration gradients for diffusion and thin layers so that diffusion distances are short.
• gill lamellae are the main site of gaseous exchange in the fish, they have a good blood supply and large surface area.
• gill filaments occur in large stacks (gill plates) and need a flow of water to keep them apart, exposing the large surface area needed for gaseous exchange.

Question 2

water flow over the gills

Answer 2

• when fish are swimming they can keep a current of water flowing over their gills simply by opening their mouth and operculum.
• when the fish stops moving so does the flow of water, the mouth is opened increasing the volume of the buccal cavity the pressure in the cavity decreases forcing water into the buccal cavity.
• movement of water into the buccal cavity increases the pressure of the opercula cavity as the mouth closes. This forces the water over the gills and out of the operculum

Question 3

extra adaptations of the gills

Answer 3

• the tips of adjacent filaments overlap, this increases resistance to flow of water over the gill surfaces and slows down the movement of water so there is more time for gaseous exchange.
  -the water moving over the gills and the blood in the filaments move opposite directions. A steep concentration gradient is needed for fast diffusion to take place. A countercurrent exchange system is set up. This adaptation ensures that steeper concentration gradients are maintained and as a result more gaseous exchange can take place.