Animals that do not use energy to maintain body temperature, like amphibians and many reptiles, can tolerate some mixing of oxygenated and deoxygenated blood. Therefore, they have three-chambered hearts.
Why do some animals, such as amphibians and many reptiles, have three-chambered hearts?
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Amphibians and many reptiles have three-chambered hearts due to their semi-aquatic lifestyles and metabolic adaptations. In these organisms, a single ventricle partially separates oxygenated and deoxygenated blood, allowing some mixing. This facilitates oxygen supply during both aquatic and terrestrial phases of their lives. While less efficient than four-chambered hearts, this adaptation is metabolically suitable for ectothermic animals, optimizing oxygen delivery for varying activity levels. Three-chambered hearts strike a balance between oxygenation efficiency and energy conservation, reflecting the evolutionary compromise in species like amphibians and reptiles that transition between aquatic and terrestrial environments.