| How have fish adapted to low concentration of oxygen in water | - each gill is made of lots of thin branches called gill filaments or primary lamellae, which give a big surface area for exchange of gases
- the gill filaments are covered with lots of tiny structures called gill plates or secondary lamellae, which increases the surface area more
- the gill plates have lots of blood capillaries and a thin surface layer of cells to speed up diffusion |
| Explain counter current system | - blood flows through the gill plates in one direction and the water flows over in the opposite direction
- this maintains a large concentration gradient between water and the blood
- the concentration of oxygen in the water is always higher than in the blood, so as much oxygen as possible diffuses from the water into the blood |
| Explain ventilation in fish | - fish opens its mouth, which lowers the floor of the buccal cavity
- the volume of the cavity increases, decreasing the pressure inside it
- water is then sucked into the cavity
- when the fish closes its mouth, the floor of the buccal cavity is raised again
- volume inside decreases, pressure increases, and water is forced out of the gill filaments |
| What is the operculum | - it is a bony flap that covers each gill filament protecting it
- the increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills |
| Explain ventilation in insects | - they have microscopic are filled pipes called trachea
- air moves into the trachea through pores on the insect's surface called spiracles |
