Germ layer is a primary layer of cells found in the embryo. The three primary germ layers that generate most of the cells in the developing mammalian forelimb are ectoderm, mesoderm and endoderm.
Ectoderm forms the outer component of a mammalian body such as skin, hair, etc. Endoderm forms the inner layer that comprises of the linings of digestive system, lungs and thyroid. Mesoderm is the middle layer that forms the skeletal system, heart, etc.
Neural tube is generated by the inward folding of the ectoderm. This process is called neurulation. Ectoderm also forms neural crest.
This is only one part of the answer, but its important: high-altitude O2 absorbs much energy from the sun (including radioactivity), which forms the ozone layer. this process protects delicate molecules important to life - most notably dna
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B. The mutations were beneficial for each new environment.
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Answer: food and drug administration
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