gaseous exchange in fish

Question 1

how does gas exchange occur in bony fish?

Answer 1

in bony fish, gas exchange occurs over the surface of the gills which consists of four pairs of gill arches, consisting of many gill filaments. these are protected by the operculum.

Question 2

how are gills adapted for gaseous exchange?

Answer 2

1. large surface area : provided by the presence of a large number of gill filaments. these filaments possess lamellae increasing the surface area even further.
2. short diffusion pathway : present as the blood and water are separated by a thin barrier consisting mainly of two cell layers
   - the epithelial layer of the gill lamellae
   - the endothelial layer of the blood capillaries
3. high diffusion gradient : maintained by
   - the circulatory system ensures continual flow of blood through the respiratory surface to absorb oxygen and remove carbon dioxide.
   - the ventilation mechanism which provides a continual flow of water over the gills bringing more oxygen and removing carbon dioxide.
   - the blood and water flowing in opposite directions (countercurrent system) which ensures that the blood continually meets water with a higher oxygen concentration so that a diffusion gradient is maintained along the whole length of the lamellae. diffusion always occurs across the entire length of the lamellae.