Biological Systems MCAT Practice Exam

Which germ layer is responsible for forming the nervous system?

1. Ectoderm

2. Mesoderm

3. Endoderm

4. Exoderm

The correct answer is: Ectoderm

The ectoderm is the germ layer that gives rise to the nervous system, including the brain, spinal cord, and peripheral nerves. During embryonic development, the ectoderm also contributes to the formation of the epidermis (the outer layer of the skin) and other structures such as hair and nails. The differentiation of the ectoderm into neural tissue occurs through a process called neurulation, which leads to the formation of the neural tube, the precursor to the central nervous system. In contrast, the mesoderm is primarily responsible for forming structures such as muscles, bones, and the circulatory system, while the endoderm develops into internal organs such as the gastrointestinal tract and lungs. The term "exoderm" is not recognized in biological classifications and is likely a fictional or erroneous term. Understanding the roles of these primary germ layers is crucial for grasping developmental biology and the formation of various tissues and organs during embryogenesis.