Sample Problem

Choose from the following to label the descriptions. Write the corresponding letters in the correct blank (eg: “A”).

(A)  Endoderm

(B)   Mesoderm

(C)   Ectoderm

innermost layer

becomes the skin and parts of the nervous system

becomes the blood muscles and bones

becomes the digestive system

not present in diploblastic organisms


The answers are as follows: A, C, B, A, B.

(A) The endoderm is the internal layer that becomes the digestive system.

(B) The mesoderm is the middle layer that forms the blood muscles and bones, and is only present in triploblasts (organisms with three layers of specialized tissue).

(C) The ectoderm is the outermost layer that forms the skin and part of the nervous system.