Respiratory system

3. Small openings on an insect's body that connect to the tracheal system.
5. The structure that supports the gills in fish.
8. The gas that organisms need to carry out metabolic functions.
10. The type of fluid in some animals where oxygen diffuses instead of blood.
12. The process by which gases move from high to low concentration.
14. The respiratory organ used by earthworms and amphibians.

1. The type of circulatory system that transports oxygen in larger organisms.
2. The system in insects that delivers oxygen directly to their body tissues.
4. The group of organisms that includes flatworms and relies on direct diffusion.
6. The type of organism that relies on diffusion across its outer membrane for gas exchange.
7. The respiratory organ used by fish to extract oxygen from water.
9. The waste product removed by the respiratory system.
11. The material that makes up the tubes in an insect's tracheal system.
13. The shape of flatworms that helps increase surface area for diffusion.