Answer: core
Explanation:
The core is the thickest layer of the Earth, and the crust is relatively thin, compared to the other layers.
The four bases in DNA are: adenine, thymine, cytosine, guanine.
In RNA, thymine gets replaced by uracil.
Purine is only a name for the two bases guanine and adenine.
Answer:
The endoderm gives rise to the nervous system.
Explanation:
Gastrulation is the process that occurs during the third week of embryonic development and includes transformation of embryonic disc with epiblast and hypoblast into a three layered embryonic disc made up of ectoderm, mesoderm and endoderm. These are the three primary germ layers and give rise to various tissues and body organs.
Endoderm of the embryo give rise to epithelial lining of gastrointestinal tract (except the buccal cavity), respiratory tracts and other organs such as gallbladder, liver,etc. Mesoderm forms connective tissues such as bones as well as muscles and peritoneum. All the tissues of nervous system and epidermis of skin are derived from ectoderm.