Which of the following is NOT a primary germ layer? Group of answer choices
ectoderm
mesoderm
trophoderm
endoderm
The correct answer and explanation is:
The correct answer is trophoderm.
In early embryonic development, the three primary germ layers—ectoderm, mesoderm, and endoderm—form the foundation of the body’s structure. These layers give rise to all the tissues and organs of the body.
- Ectoderm: This outer layer develops into structures like the skin, hair, nails, and the nervous system. It gives rise to the brain, spinal cord, and peripheral nerves, as well as the epidermis of the skin.
- Mesoderm: This middle layer forms structures like muscles, bones, the circulatory system, kidneys, and reproductive organs. It also contributes to the formation of connective tissues such as cartilage and ligaments.
- Endoderm: The innermost layer forms the digestive system, lungs, liver, pancreas, and other internal organs. It also gives rise to the epithelium of the gastrointestinal tract and respiratory system.
The trophoderm, on the other hand, is not one of the primary germ layers. It refers to the outer layer of the trophoblast, a structure involved in the formation of the placenta during pregnancy. While trophoderm cells contribute to the formation of the placenta, they are not considered a germ layer responsible for developing the body’s tissues and organs.
Therefore, the trophoderm is not a primary germ layer, and it is distinct from the ectoderm, mesoderm, and endoderm, which are directly responsible for the formation of the major tissues and organs in the body.