Which germ layer is responsible for forming the lining of the digestive tract?

The germ layer responsible for forming the lining of the digestive tract is the endoderm. During the process of embryonic development, the endoderm gives rise to the epithelial lining of the gastrointestinal tract, as well as the respiratory tract and several associated structures such as the liver and pancreas.

The endoderm forms the innermost layer of the three primary germ layers during gastrulation. As the embryo develops, this layer will differentiate into various organs and systems essential for digestion and metabolism.

In contrast, the ectoderm is primarily responsible for forming structures such as the skin, hair, and the nervous system. The mesoderm gives rise to muscle, bone, and connective tissues, among other systems, but is not involved in forming the lining of the digestive tract. The option stating "All of the above" is inaccurate since only the endoderm is specifically associated with the formation of the digestive system lining.