Question

Skeleton and muscles in a vertebrate embryo develop from
A. Ectoderm
B. Mesoderm
C. Endo-mesoderm
D. Endoderm

Answer 1

During gastrulation, the blastula folds in on itself and cells migrate to construct the three layers of cells in a pattern, the gastrula, with a sunken space that will serve as the digestive tract. Each of the layers of cells is called a germ layer and will differentiate into different organ systems. The three germ layers are endoderm, ectoderm, and mesoderm. Tissues and embryonic organs develop from cells in each germ layer.

Complete explanation:
Option A: Epidermis, hair, nails, the lens of the eye, sebaceous glands, cornea, tooth enamel, and the epithelium of the mouth and nose are all formed from the surface ectoderm. The peripheral nervous system, adrenal medulla, melanocytes, and facial cartilage all emerge from the neural crest of the ectoderm.
Hence, option A is incorrect.
Option B: Intermediate mesoderm, paraxial mesoderm, lateral plate mesoderm, and chorda-mesoderm are all mesoderm components that grow into tissues. The cartilage, skeletal muscle, and dermis grow from the paraxial mesoderm. Muscle (both smooth and striated) and skeletal system bones are also formed by the mesoderm.
Hence, option B is correct.
Option C: The separation of mesodermal cells from the original common mass of endomesoderm is one method of mesoderm formation. This may take the form of single cells separating from the archenteron or whole sheets of cells separating from the endoderm. The gastrulation of amphibians is an example of the latter kind.
Hence, option C is incorrect.
Option D: Except for a portion of the mouth and pharynx, and the terminal part of the rectum, the endoderm forms the epithelial lining of the entire digestive tract (which are lined by involutions of the ectoderm). It also makes up the lining cells of the liver and pancreas, as well as the epithelium of the auditory tube and tympanic cavity, the trachea, bronchi, and alveoli of the lungs, the bladder and a section of the urethra, the thyroid gland, and the thymus follicular lining.
Hence, option D is incorrect.

Hence, Option B is the correct answer.

Note:
Gastrulation results in the creation of three germ layers, each of which gives birth to a separate organ in the animal's body as it develops. Organogenesis is the name for this process. Organs emerge from the germ layers via a differentiation phase. Embryonic stem cells express complex sets of genes that decide their ultimate cell type during differentiation. Any cells in the ectoderm, for example, can express genes unique to skin cells. As a result, these cells will resemble epidermal cells in form and behavior. The process of differentiation is regulated by location-specific chemical signals from the cell's embryonic environment, which cause a series of events that control gene expression.