2. Gas exchange in insects

4. Gases enter and leave the tracheal system through spiracles

6. Spiralling strands of chitin in the walls of the trachea make these tubes fairly rigid and thus protect them from being compressed by the surrounding tissues

7. O2
CO2

8. Large surface area provided by the extensive network of tracheoles, which is further increased when fluid is withdrawn from the tracheoles during periods of high metabolic activity
Steep concentration gradients are maintained between the tracheoles and body cells due to tissue respiration
In larger, more active insects, the pumping movements of the abdomen increase the steepness of these diffusion gradients to meet the metabolic demands of the organism
A short diffusion path exists between the thin tracheole walls and the tissues
The continual flow of air through the tracheal system maintains the ventilation of the tissues

9. This image shows a stag beetle, one of the largest of all insects
This image shows a stag beetle, one of the largest of all insects. It can grow to widths of 5cm. Using your knowledge of the insect respiratory system explain why insects do not get much bigger than this…

10. Lactic acid reduces the water potential of the cells and water diffuses from the tracheoles by osmosis back into the cells.
Air moves in to replace the fluid, and gases diffuse more rapidly across the air-filled tracheoles O2
CO2