Why is it difficult for scientist to find fossils from the pre-Cambrian period

1. The upper chambers of the heart are the

2. The lower chambers of the heart are the

3. When both ventricles relax and refill this is the

4. When both ventricles contract and pump the blood out through another series of valves this is the.

Q 5-6 Select Physiology.

5. Oxygen poor blood flows from the right atrium to the right ventricle that pumps blood out through the to the lungs.

6. The freshly oxygenated blood returns to the left atrium of the heart by way of the .

Q 7-10 Select Continue.

7. Oxygen rich blood flows down through the left atrium to fill the left ventricle, which pumps into the .

8. Blood flows from the aorta into smaller , which carry it to all body organs and tissues.

9. From the arterioles, blood flows into thin walled blood vessels called .

10. After flowing through venules, then veins, eventually all blood enter either the superior or inferior which empty into the heart.

Explanation: