Optometry Admission Test (OAT) Practice

What key structures are formed during gastrulation?

1. Skeleton and muscles

2. Ectoderm, endoderm, and mesoderm

3. Nervous system and blood vessels

4. Digestive tract and lungs

The correct answer is: Ectoderm, endoderm, and mesoderm

During gastrulation, the embryonic cells undergo significant rearrangement to form the three primary germ layers: ectoderm, endoderm, and mesoderm. Each of these layers gives rise to specific structures and systems in the developing organism. The ectoderm is responsible for forming the outer layer of the skin, hair, nails, and the entire nervous system, including the brain and spinal cord. The endoderm develops into the inner linings of the digestive tract, respiratory tract, and various organs such as the liver and pancreas. The mesoderm, which lies between the ectoderm and endoderm, differentiates into muscles, bones, the circulatory system, and other internal structures. Gastrulation is a critical phase in development because it not only establishes these layers but also sets the stage for later organogenesis, where specific organs develop from these germ layers. Thus, recognizing that gastrulation's main outcome is the formation of the ectoderm, endoderm, and mesoderm is fundamental for understanding early embryonic development and the organized structure of an organism.