The body's breathing system
The body's system of nerves
The body's food-processing system
The body's blood-transporting system
Oxygen helps the blood to clot.
Oxygen is necessary for cell growth and energy.
Oxygen brings food to the cells.
Oxygen is not important -- carbon dioxide is the most important substance to the body.
The blood vessels and capillaries
Transporting materials throught your whole body
Lets you breath
The heart, blood, and blood vessels.
The heart, the brain, and the lungs.
The lungs, the blood, and the blood vessels.
The brain, the heart, and the blood vessels.