Final answer:
The difference between a one and two-chambered circulatory system lies in the presence of mixing of oxygenated and deoxygenated blood. Animals with a two-chambered heart, like fish, have more efficient oxygenation than those with a three-chambered heart, like amphibians and reptiles.
Step-by-step explanation:
A three-chambered heart is found in amphibians and reptiles, while fish have a two-chambered heart. The key difference between these two circulatory systems is the presence of mixing of oxygenated and deoxygenated blood. In a three-chambered heart, there is some mixing of blood in the ventricle, which reduces the efficiency of oxygenation, while in a two-chambered heart, there is no such mixing. This results in better oxygenation and more efficient movement of oxygen around the body in animals with a two-chambered heart.