21.
Part 1: Is it appropriate to describe a human heart as a "double pump?' (explain the term double pump and provide a detailed explanation that supports your answer)
Part 2: How is the systemic circuit different from the pulmonary circuit? Provide and explain at least 4 differences between these circuits
Part 3: A patient has an opening between the right and left atria. How, if at all, would this impact the state of oxygenation of the pulmonary or systemic circuit blood?

Part 1. Yes, the term is appropriate. The heart pumps oxygenated blood to the head and the body and the deoxygenated blood to the lungs.

Part 2. The main difference is that the pulmonary circuit carries the blood to the lungs and back to the heart and the systemic circuit carries the blood from the heart to the body and back.

Part 3. It wouldn't impact the state of oxygenation by much.

Explanation:

Part 1.  Deoxygenated blood from the body enters the heart through the vena cava to the right atrium, through the right ventricle to the pulmonary artery to the lungs. It gets oxygenated in the lungs and sent back to the heart by the pulmonary vein, through the left atrium, left ventricle to the aorta and back to the body. The process requires the heart to pump blood to the lungs and to the body; hence the "double pump".

Part 2. The bloodflow in the systemic circuit would be slower the oxygenation process from the lungs would continue and the impact wouldn't do too much damage. Some animals actually do have this opening. (e.g. crocodiles).