What is a coelom (true body cavity)? a.A body cavity partially lined with mesoderm b. A body cavity lined with endoderm 0 c The body cavily of a sponge d.A body cavity completely lined with mesoderm
The Correct Answer and Explanation is:
The correct answer is d. A body cavity completely lined with mesoderm.
A coelom, often called a true body cavity, is a fundamental feature used to classify many animals. It is a fluid filled space that is located between an animal’s digestive tract and its outer body wall. The defining characteristic of a true coelom is that it is entirely enclosed by tissue derived from the mesoderm, one of the three primary germ layers formed during embryonic development.
During the development of an animal with a coelom, or a coelomate, the mesoderm splits to form two distinct layers. One layer, the parietal peritoneum, adheres to the inner surface of the body wall, which is derived from the ectoderm. The other layer, the visceral peritoneum, covers and supports the internal organs, including the digestive tube, which is derived from the endoderm. The space between these two mesodermal layers is the coelom itself.
This complete mesodermal lining is critically important. It allows for the development of complex organ systems and provides space for these organs to grow, move, and function independently of the body wall. For example, your heart can beat and your intestines can churn without causing your entire body to visibly contort. The coelomic fluid can also act as a hydrostatic skeleton in some invertebrates, like earthworms, aiding in locomotion.
This structure is distinct from other body plans. Acoelomates, like flatworms, have no body cavity at all; the region between their gut and body wall is filled with solid mesodermal tissue. Pseudocoelomates, like roundworms, have a body cavity that is only partially lined with mesoderm. In their case, the mesoderm lines the outer body wall, but it does not cover the gut, which is in direct contact with the cavity’s fluid. Therefore, the complete mesodermal lining is the key feature that distinguishes a true coelom.
