Which of the following is the missing primary germ layer alongside the mesoderm and endoderm?

• A. Blastoderm
• B. Ectoderm
• C. Periderm
• D. Epidermis

Answer: (B)

Verified step by step guidance

1. Understand the concept of primary germ layers: During embryonic development, three primary germ layers form—ectoderm, mesoderm, and endoderm. These layers give rise to all tissues and organs in the body.
2. Identify the missing germ layer: The problem states that mesoderm and endoderm are already mentioned, so the missing germ layer must be the third primary germ layer, which is the ectoderm.
3. Clarify the role of the ectoderm: The ectoderm is responsible for forming structures such as the epidermis (outer skin layer), nervous system, and sensory organs.
4. Eliminate incorrect options: The blastoderm is a structure in early embryonic development, not a germ layer. The periderm is a temporary layer of skin during development, and the epidermis is derived from the ectoderm but is not a germ layer itself.
5. Conclude that the correct answer is ectoderm, as it completes the trio of primary germ layers alongside mesoderm and endoderm.