A molecular fragment of an antigen that serves as the primary signal that the molecule is foreign is called a(n) , whereas a small foreign molecule that can only elicit an immune response when linked to another larger molecule is called a(n) .

1. Air enters the bronchioles in the lungs and reaches the alveoli.

2. The air diffuses into the capillaries surrounding the alveoli.

3.The pulmonary veins carry oxygenated blood to the heart.

4.The left atrium fills with oxygen-rich blood and contracts to fill the left ventricle.

5.The oxygen-rich blood moves from the aorta and reaches the kidneys rough a series of blood vessels.

6. The capillaries join together to reach the arteries, transferring the oxygen.