Question

Explain the evolutionary arc of the circulatory and respiratory systems from Cephalochordates to the Tetrapods. Start by briefly defining circulatory and respiratory systems. Your answer should clarify how each of the systems has changed, the adaptive significance of these changes during this time, and in which extant lineages we still see evidence of these different stages of evolution.

Answer 1

The circulatory system circulated blood throughout the body of an organism. It transports oxygen along with other essential nutrient to the tissues of the body. The respiratory system removes the carbondioxide from the body and takes in oxygen, which is then circulated thorughout the body by the circulatory system.

The circulatory systems of the cephalochordates is closed but they do not have a heart to pump the blood. MOreover, the blood is unpigmented as it only transports the nutrients rather than the gaseous exchange. However, in the tetrapods, the closed circulatory system has a central pump (heart) that pumps the pigmented blood throughout the body. The larger body of the tetrapods and greater energy requirement for the body functioning might have resulted in the evolution of the central pump. Moreover, the heart is divided into chambers that allows for the efficient separaton of the deoxygenated and oxygenated blood.

The respiratory system of tetrapods have lungs which is used for the gaseous exchange. The lungs might have evolved from the sac-like structures in the primitive fishes. The lungs allow for a quicker exchange of the gases as the surface area is increased.