fish

• structure of bony fish gills

  gill on each side of the head, 4 gill arches each with 2 rows of filaments, lamellae on filaments at right angle
• adaptations of the gills

  many thin lamellae on the filaments for large surface area, walls of lamellae and filaments being a single layer of flat epithelial cells for short diffusion distance, dense network of capillaries and constant flow of water through gills to maintain steep concentration gradient
• mouth opens, operculum closes. buccal cavity floor is lowered, increase volume, decrease pressure. water flows down pressure gradient into the buccal cavity. opercular cavity expands, buccal cavity floor raised, increase pressure, decrease volume. water moves to opercular cavity across gills. opercular cavity constricts, increase pressure, decrease volume. operculum pushed open, water moves out down pressure gradient.
• what is the counter current mechanism

  water flowing over lamellae, blood flowing through lamellae in opposite directions. maintaining a diffusion gradient along the whole length of the gill. water always has a higher oxygen conc. as much oxygen as possible diffused into blood.
• what happens when temperature of water increases

  the solubility of oxygen in water decreases, rate of ventilation will increase to take in the same volume of oxygen