Which term denotes the outer layer?

• A. Endoderm
• B. Ectoderm
• C. Mesoderm
• D. Epithelium

Answer: (B)

The outermost layer in early development is the ectoderm. During gastrulation, the embryo forms three germ layers: ectoderm on the outside, mesoderm in the middle, and endoderm on the inside. The ectoderm gives rise to structures like the skin (epidermis) and the nervous system, which is why it’s described as the outer layer. Epithelium, while a common tissue type that lines surfaces, can originate from different germ layers depending on the body region, so it’s not used to name the outermost layer.