Why is it a disadvantage to have 2-chambered heart?

Two-chambered hearts, as seen in fish, are not necessarily disadvantageous. Here's why:

Limited Pulmonary Circulation: Two-chambered hearts are primarily found in fish and amphibians. Fish mainly rely on gills for oxygen exchange, and thus, their hearts are adapted for a single circulatory circuit. Oxygen-poor blood is pumped to the gills, where it picks up oxygen, and then returns to the rest of the body. Compared to the more efficient four-chambered hearts found in mammals and birds, two-chambered hearts mix oxygenated and deoxygenated blood, which limits systemic oxygen delivery.

Lower Metabolic Demands: Fish and amphibians typically have lower metabolic demands than birds and mammals. Their slower metabolism means that they require less oxygen and can function effectively with the simpler circulatory system of a two-chambered heart.

Efficient Oxygen Extraction: Aquatic environments can be richer in oxygen than terrestrial environments. Fish and amphibians have specialized structures, such as gills, which enable efficient oxygen extraction from the water. This reduced reliance on the cardiovascular system for oxygen delivery compensates for the limitations of a two-chambered heart.

Overall, while two-chambered hearts might seem less efficient compared to four-chambered hearts, they are well-adapted to the specific needs and environments of fish and amphibians. These organisms have evolved to meet their oxygen requirements with the circulatory systems they possess.