Question

True coelom is lined by:
A. Ectoderm
B. Ectoderm and endoderm
C. Mesoderm
D. Endoderm

Answer 1

Hint: Coelom a characteristic of multicellular organisms. A coelom is defined as a body cavity present between the body wall and the digestive tract. The internal cavity is filled with a fluid-like substance. Organisms in which coelom is present are termed as acoelomates or Coelomates.

Complete answer:
True coelom is lined by Mesoderm.
The body consists of three germ layers, viz., Ectoderm, endoderm and mesoderm. The middle layer, mesoderm surrounds the coelom. Annelids, Molluscs, Arthropods, Echinoderms possess true coelom and are called coelomates. The ectoderm is the outermost germ layer and the endoderm being the innermost.
In the case of the pseudocoelomates and acoelomates, true coelom surrounded by mesoderm is not present. In Pseudocoelomates a true coelom is not present and the fluid-filled space is surrounded by mesoderm as well as endoderm. In acoelomates no fluid-filled cavity is present.
Aschelminthes are Pseudocoelomates and Coelenterata and Platyhelminthes fall under the acoelomate category. The cavity in some organisms like cockroaches gets filled with blood and is called haemocoel. The coelom development occurs during the gastrulation phase of embryo development. Gastrulation is the process when the germ layers form just after the process of blastulation.
The main function of the coelom is to provide protection to the internal organs by acting as a cushion.
Ectoderm is the outermost germ layer and does not cover the coelom. Ectoderm surrounds the mesoderm. So, Option a) is incorrect.
It is not possible for both endoderm and ectoderm to surround the coelom. As the mesoderm comes in between. So, Option b) is incorrect.
It is not possible for both endoderm and ectoderm to surround the coelom. As the mesoderm comes in between.
Endoderm is present inner to the coelom and does not enclose the coelom. So, Option d) is incorrect.

Hence, the correct answer is option (C).

Note: Coelom, an important protective fluid-filled structure is surrounded by the mesodermal lining. The other two germ layers are the ectoderm and the endoderm. The mesoderm lying in between the other two layers encloses the coelom.