Gas exchange surfaces fish

• Describe the gas exchange surface of a fish

  Gill arches have many filaments stacked up along them. Each filament has a series of flattened discs called gill lamellae that increase the surface area of the filaments. Water is taken in through the mouth and it flows over the gills then is forced out through openings on the side of the head.
• Describe and explain how the gas exchange surface of a fish is adapted

  Large surface area so increases the rate of diffusion; Thin epithelium so there is a short distance between water and blood; Water and blood flow in opposite directions so an equilibrium is not reached and diffusion can occur along the length of the filaments, as water is always next to blood that has a lower concentration of oxygen; Circulation replaces blood saturated with oxygen so the concentration gradient is maintained; Ventilation replaces water as oxygen removed so the concentration gradient is maintained;
• Describe and explain how the counter current system leads to efficient gas exchange across the gills of a fish

  Water and blood flow in opposite directions; this opposite flow maintains concentration gradient as water is always next to blood with a lower concentration of oxygen;

  Along the entire length of the gill filament.
• Describe how a fish ventilates

  Water that is rich in oxygen enters the mouth of the fish (buccal cavity).

  The mouth closes, the floor of the mouth moves upwards.

  This decreass the volume of the buccal cavity, increasing the pressure which forces the water over the surface of the gills then out through the operculum (holes at the side of the head)