Final answer:
Amphibians have a three-chambered heart with two circulatory routes, resulting in some mixing of oxygenated and deoxygenated blood. A ventricular ridge partially separates the blood, ensuring efficient circulation for a dual aquatic and terrestrial lifestyle.
Step-by-step explanation:
Amphibians, such as frogs, possess a three-chambered heart with two atria and one ventricle. Unlike fish with a simpler two-chambered heart that results in a single circulatory flow, amphibians have a more complex circulation involving two circulatory routes: one for oxygenation of the blood through the lungs and skin, and another for delivering oxygen throughout the body.
This allows amphibians to function in both aquatic and terrestrial environments. However, the presence of only one ventricle means there is some inevitable mixing of oxygenated and deoxygenated blood, which can reduce the efficiency of oxygen transport in comparison to separate systems found in mammals and birds. Nevertheless, a ridge within the amphibian ventricle helps to route oxygen-rich blood through the systemic circuit and deoxygenated blood back to the lungs and skin for re-oxygenation.