In the circulatory system, the heart acts as the pump, the vessels are conduits allowing blood and lymph flow, and the transport fluid is the blood, which can deliver nutrients and oxygen to tissues and cells throughout the body. Thus, the primary purpose of the circulatory system is, as the correct answer choice states, to deliver oxygen to tissues and transport blood and lymph.

The respiratory system is responsible for gas exchange, while the excretory system is responsible for maintaining fluid balance. The immune system is responsible for destroying foreign pathogens.

There can be two classes of antigens on blood cells: one can distinguish ABO blood types and the second is the Rhesus factor (Rh factor), which determines positive or negative blood type.

A person with type O blood would not carry any antigens on their cells; however this individual’s plasma would contain anti-A and anti-B antibodies. Interestingly, this is why type O blood individuals are commonly known as universal donors, as their cells do not elicit immune responses from any other blood cell types. An individual with Rh^- would not carry the Rh factor antigen on the surface of their cells. Thus, O^-, correctly identifies the blood type of an individual lacking any of these antigens on their blood cells.

All of the given answer options are contained in blood at some point; however the main components are red blood cells (RBC’s), platelets, plasma, and white blood cells (WBC’s). Platelets are involved in coagulation, while white blood cells are involved in immunity. Plasma refers to the fluid matrix of the blood, and contains proteins, gases, amino acids, and hormones.

Hemoglobin is a specific protein located in red blood cells. Oxygen binds to hemoglobin for transport through the boold. Neither of these are considered major components of blood.

The universal donor blood type is O^-, because this blood can be transfused to any of the ABO blood types, as well as to those with Rh+ and Rh-. O-negative blood is devoid of any antigens, but carries antibodies against A, B, and Rh.

AB⁺ contains both A and B antigens that would elicit an immune responses against any blood containing anti-A or anti-B antibodies. However, AB blood can receive all types of blood because it contains no antibodies. Additionally, AB⁺ blood carries the Rh antigen and is void of Rh antibodies. This makes AB⁺ blood the universal acceptor.

The aorta is the largest artery in the body. Like other arteries, the aorta's walls are made up of several layers, one of the largest layers being an elastic layer, which stretches and recoils in response to high pressure blood being pumped through it. Also, recall that all arteries carry blood away from the heart. Blood from the left ventricle of the heart is pumped into the aorta through the aortic semilunar valve. The venae cavae are the largest veins in the body. Like all veins, they carry blood back to the heart. Although the pulmonary artery is quite large, it is not as large as the aorta. Recall that the left ventricle is larger than the right ventricle, and thus more blood is pumped from the left ventricle through the aorta than is pumped from the right ventricle through the pulmonary artery.

Capillaries are the smallest blood vessels. They are responsible for diffusion of gasses and other materials across their walls. For example, alveoli in the lungs are surrounded by capillaries. There, carbon dioxide from the blood diffuses through the capillary walls, into the alveoli, to be exhaled. The opposite is true for oxygen. All of these other blood vessels have walls which are too think to allow any exchange of materials.

The name of this wall is the interventricular septum. It keeps the right and left sides of the heart separate. Remember the importance of keeping these chambers separate; the circulatory system is actually two circuits: pulmonary and systemic. Pulmonary circulation involves blood traveling from the right side of the heart to the lungs to become oxygenated, then returning to the left side of the heart where it is pumped to the body, where the oxygen is taken up by cells. Lastly, the oxygen-poor blood returns from the body to the right side of the heart and the circuit starts again. Mixing blood between these two circuits would result in compromised circulatory system function. 

Pulmonary arteries carry oxygen-poor blood from the heart to the lungs so that it can become oxygenated. Pulmonary veins carry oxygen-rich blood from the lungs back to the heart. The aorta carries oxygen-rich blood from the heart to the rest of the body and brain. The superior and inferior vena cavae carry oxygen-poor blood from the body back to the heart so that it can travel to the lungs and become oxygenated again.

Blood flows back to the heart through the pulmonary veins after being oxygenated in the lungs and re-enters the heart through the left atrium. The blood then passes into the left ventricle, which pumps an enormous volume of blood via the aorta to the rest of the body. This chamber of the heart is under a lot of pressure since the heart must pump blood through the many miles of vessels and arteries; therefore, the left ventricle wall must be thicker to withstand the force of these contractions. 

The left ventricle pumps blood into the aorta, through which oxygen-rich blood circulates throughout the body.