1. What part of the human eye controls the amount of light entering?

2. What gas do humans exhale when breathing?

3. What is the main function of red blood cells?

4. What is the only internal human organ capable of regenerating itself completely from as little as 25% of its original tissue?

5. Approximately how many miles of blood vessels are found in a single human adult?

6. What is the name of the fatty insulating layer that allows nerve impulses to travel faster?

7. Which type of sweat gland is found all over the body and is primarily responsible for temperature regulation?

8. Which protein in red blood cells uses iron to transport oxygen throughout the body?

9. Where is the largest concentration of bacteria found in the human body?

10. What are the microscopic functional units of the kidney called?

11. Approximately how often does the human body replace its taste buds?

12. Which organ in the lymphatic system acts as a major filter for the blood?

13. What is the name of the active growth phase of a hair follicle?

14. What are the microscopic hair-like structures that move mucus out of the human respiratory tract called?

15. Which part of the human eye is unique for having no blood vessels and receiving oxygen directly from the air?

16. What is the primary function of red bone marrow in the human body?

17. Where in the human body are the menisci located?

18. What are the tiny projections in the small intestine that increase surface area for nutrient absorption?

19. Which hormone is released by the parathyroid glands to increase blood calcium levels?

20. What is the name of the tough, fibrous membrane that covers the outside of a bone?