HSA 2006 Biology Item 21

Most organisms need oxygen for their cells to function normally. In mammals, two organ systems work together to move oxygen throughout the body.

The respiratory system brings oxygen into the body from the environment. Which of these body systems is directly involved in the delivery of oxygen to the major organs of the human body?

1. the nervous system
2. the digestive system
3. the endocrine system
4. the circulatory system