Unit 1 - The circulatory system

1. An organism that provides a living environment for a parasite.
6. The clear, salty liquid produced by the eyes that helps to keep them moist and can also express emotions.
8. Microscopic single-celled organisms that can be found in various environments and can cause infections or help in digestion.
10. A blood vessel that carries blood away from the heart.
11. A muscle that helps in breathing by expanding and contracting the chest cavity.
12. The upper chamber of the heart that receives blood coming into the heart.
15. A microscopic infectious agent that requires a living host to reproduce and can cause diseases such as the flu or COVID-19.
16. The lower chamber of the heart that pumps blood out to the lungs or the rest of the body.
17. The action of the heart, moving blood throughout the body.

1. The organ that pumps blood through the circulatory system.
2. A type of fungus used in baking and brewing that can also cause infections in humans.
3. The fluid that circulates through the heart, arteries, veins, and capillaries, delivering oxygen and nutrients to tissues.
4. A bone that protects the chest cavity and organs within.
5. An organism that lives on or inside another organism (the host) and benefits at the host's expense.
7. An organ where digestion of food begins with the help of stomach acids and enzymes.
9. The smallest type of blood vessel where gas exchange occurs between blood and tissues.
13. A sticky substance produced by the body to protect and lubricate tissues, especially in the respiratory and digestive systems.
14. The tube that connects the throat to the lungs, allowing air to pass through.
15. A blood vessel that carries blood towards the heart.