Final answer:
Vertebrates, specifically mammals and birds with higher metabolic rates, require a double circulatory system to efficiently carry oxygen and remove waste.
Step-by-step explanation:
Complex organisms, particularly vertebrates, require a double circulatory system for efficient transport of oxygen, nutrients, and waste.
A double circulatory system consists of separate pulmonary and systemic circuits, allowing for enhanced oxygenation of blood and more efficient delivery of oxygenated blood to the body's tissues. Higher metabolic rates of mammals and birds necessitate this division, thus avoiding mixing of oxygenated and deoxygenated blood.
Fish have a simpler, single circulatory system with a two-chambered heart. However, as organisms evolved to live on land and subsequently had greater oxygen needs, the circulatory system adapted.
Amphibians have a three-chambered heart with some blood mixing, while mammals and birds have a four-chambered heart to completely separate oxygenated and deoxygenated blood. This evolution allows for a more active lifestyle due to more efficient oxygen delivery.
In summary, the systemic circulation is responsible for delivering oxygen-rich blood to the body, while pulmonary circulation is dedicated to oxygenating blood by passing it through the lungs.
The heart, acting as two separate pumps, ensures directed blood flow through these circuits, with arteries carrying blood away from the heart and veins bringing it back. Capillaries are the sites of gas and nutrient exchange.