Which of the following lists the germ layers present in early embryonic development?

• A. Endoderm, Ectoderm, and Mesoderm
• B. Endoderm only
• C. Ectoderm and Mesoderm only
• D. Dermis

Answer: (A)

During gastrulation, the early embryo forms three primary germ layers: ectoderm, mesoderm, and endoderm. These layers organize into the body plan and give rise to all tissues and organs: ectoderm becomes the skin and nervous system, mesoderm forms muscle, bone, the cardiovascular system, and connective tissues, and endoderm lines the gut and forms many internal organs such as the liver and pancreas. So the list that includes all three germ layers is correct. The other options miss at least one layer or name a tissue (like dermis) rather than a germ layer.