Across
- 4. Muscle that aids breathing in mammals.
- 7. The largest artery, carrying blood from the heart to the body.
- 8. Organs for breathing air in reptiles, birds, mammals, and amphibians.
- 11. Pertaining to birds, which have unidirectional airflow in lungs.
- 13. Branches of the trachea that lead to the lungs.
- 15. Structure that prevents back-flow of blood in the heart.
- 16. Small openings on some arthropods and cartilaginous fish for air intake.
- 18. Wall that separates heart chambers.
- 19. Vertebrates with a single circulatory loop and two-chambered heart.
- 20. Tiny air sacs in mammalian lungs for gas exchange.
Down
- 1. Muscular organ that pumps blood through the circulatory system.
- 2. Oxygen-carrying protein in red blood cells.
- 3. Organs used for gas exchange in fish and some amphibians.
- 5. The fluid part of blood.
- 6. Heart chamber that pumps blood out to the body or lungs.
- 9. Microscopic vessels where oxygen and nutrients are exchanged.
- 10. Network of tubes used by insects to breathe.
- 12. External openings for air intake; also known as nostrils.
- 14. Common exit cavity for digestive, urinary, and reproductive systems in some animals.
- 17. Type of circulation with separate pulmonary and systemic loops.