Circulatory systems of amoeba, fish and mammals...?

Question

What are the differences?
How are they designed to fit their purposes?

Answer 1

Amoeba has a single nucleus, and a simple contractile vacuole which maintains its osmotic pressure, as its most recognizable features. It obtains its food by phagocytosis.
Although simple in form, amebas are very successful organisms and are found abundantly in a variety of habitats all over the world. Amebas live in freshwater, the oceans, and in the upper layers of the soil, and many have adapted to a parasitic life on the body surface of aquatic animals or in the internal organs of both aquatic and terrestrial animals. Few animals escape invasion by some type of ameba. Some are harmless, but others are pathogenic and cause serious diseases
Freshwater amebas take up water constantly through the process of osmosis, and water content is regulated with a pulsating contractile vacuole. Marine amebas lack a contractile vacuole. Respiration is by diffusion of gases through the cell membrane.


Fish have a closed circulatory system with a heart that pumps the blood in a single loop throughout the body. The blood goes from the heart to gills, from the gills to the rest of the body, and then back to the heart. In most fishes, the heart consists of four parts: the sinus venosus, the atrium, the ventricle, and the bulbus arteriosus. Despite consisting of four parts, the fish heart is still a two-chambered heart. The sinus venosus is a thin-walled sac that collects blood from the fish's veins before allowing it to flow to the atrium, which is a large muscular chamber. The atrium serves as a one-way compartment for blood to flow into the ventricle. The ventricle is a thick-walled, muscular chamber and it does the actual pumping for the heart. It pumps blood to a large tube called the bulbus arteriosus. At the front end, the bulbus arteriosus connects to a large blood vessel called the aorta, through which blood flows to the fish's gills.

Poorly oxygenated blood collects in two major veins: the superior vena cava and the inferior vena cava. The superior and inferior vena cava empty into the right atrium of the heart. The coronary sinus which brings blood back from the heart itself also empties into the right atrium. The right atrium is the larger of the two atria, although both receive the same amount of blood. The blood is then pumped through the tricuspid valve, or right atrioventricular valve, into the right ventricle. From the right ventricle, blood is pumped through the pulmonary semi-lunar valve into the pulmonary artery. This blood leaves the heart by the pulmonary arteries and travels through the lungs, where it is oxygenated, and into the pulmonary veins. The oxygenated blood then enters the left atrium. From the left atrium, the blood then travels through the bicuspid valve, also called the mitral or left atrioventricular valve, into the left ventricle. The left ventricle is thicker and more muscular than the right ventricle because it pumps blood at a higher pressure. Also, the right ventricle cannot be too powerful or it would cause pulmonary hypertension in the lungs. From the left ventricle, blood is pumped through the aortic semi-lunar valve into the aorta. Once the blood goes through systemic circulation, peripheral tissues will extract oxygen from it, and it will again be collected inside the vena cava and the process will continue. Peripheral tissues do not fully deoxygenate the blood, so venous blood does have oxygen, but in a lower concentration than in arterial blood.

Answer 2

A fish circulatory system has only a single circuit, so it's only a single pump. A mammal circulatory system is a double circuitl, so it's a double pump.