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| Question | Answer |
| Describe the structure of the gills | Each gill is made up of lots of thin plates called gill filaments/primary lamellae (large surface area) The filaments are covered in gill plates/secondary lamellae (large surface area) Each gill is supported by a gill arch The gill plates have lots of blood capillaries and a thin layer of cells to speed up diffusion |
| What is the counter-current system? | The counter-current system means that the water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen. This maintains a steep concentration gradient and as much oxygen as possible diffuses from the water into the blood |
| Outline the process of ventilation in fish | 1. Mouth opens, buccal cavity floor is lowered 2. Volume of buccal cavity increases and pressure decreases 3. Water rushes into the mouth down a pressure gradient 4. Opercular cavity expands (contributes to decrease in pressure) 5. Mouth closes, buccal cavity floor is raised 6. Volume decreases and pressure increases (higher than in the opercular cavity) 7. Water moves from buccal cavity over the gills into opercular cavity 8. Increase in pressure forces operculum to open 9. Water rushes out of the fish through the operculum |
| What is the name for the gas exchange system in insects? | Tracheal system |
| Describe the tracheal system | Air moves into the tracheae through spiracles. The trachea branch off into tracheoles which have thin, permeable walls and go to individual cells. The tracheoles also contain fluid which oxygen dissolves in; the oxygen then diffuses from this fluid into the cells. CO₂ diffuses in the opposite direction. |
| Complete the sentences: Insects uses rhythmic ____________ movements to change the ________ of their bodies and move air in and out of the ___________. Larger insects use their _______ movements to pump their ___________ too. | Insects uses rhythmic ABDOMINAL movements to change the VOLUME of their bodies and move air in and out of the SPIRACLES. Larger insects use their WING movements to pump their THORAXES too. |
| Insects usually have hairs around the spiracles. Why? | Hairs around spiracles trap humid air They minimise bulk air movement around the spiracle, and thus minimise water loss |
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