Question

1. The molecular and cellular processes in vertebrate embryos used to establish the body axes and specify cells as belonging to the three germ layers, endoderm, mesoderm and ectoderm. Be able to use experimental evidence to support or explain the process.

Answer 1

Ectoderm is one of the three primary germ layers in the very early embryo .The other two layers are the mesoderm (middle layer ) and endoderm (most proximal layer ) , with the ectoderm as the most exterior (or distal ) layer .It emerges and originates from the outer layer of germ cells.

Organogenesis is the process by which the three germ tissue layers of the embryo , which are the ectoderm , endoderm , and mesoderm , develop in to the internal organs of the organism .

A germ layer is a group of cells in an embryo that interact with each other as the embryo develops and contribute to the formation of organs and tissues , All animals , except perhaps sponges , from two or three germ layers .The germ layers develop early in embryonic life , through the process of gastrulation .During gastrulation a hollow cluster of cells called a blastula recognizes into two primary germ layer : an inner layer , called endoderm , and an outer layer , called ectoderm . Diploblastic organisms have only the two primary germ layers , these organisms characteristically have multiple symmetrical body axes , as is true of jellyfish , sea anaemones , and the rest of the phylum cnideria .All other animals are triploblastic , as endoderm and ectoderm interact to produce a third germ layer will give rise to every organ in the body , from skin and hair to the digestive tract .

Gastrulation differs across species , but the general process is the same : the hollow ball of cells that forms the blastula differentiate in to layers . The first phase of gastrulation produces a two - layered organism comprised of ectoderm and endoderm .The ectoderm will form the outer components of the body such as skin , hair , and mammary glands , as well as part of the nervous system .Following gastrulation , a section of the ectoderm folds inward , creating a groove that closes and forms an isolated tube down the dorsal mid - section of the embryo .This process of neurulation forms the neural tube , which gives rise to the central nervous system .During neurulation , ectoderm also forms a type of tissue called the neural crest , The mesoderm forms skeletal muscle , bone , connective tissue , the heart , and the urogenital system , Due to the evolution of the mesoderm , triploblastic animals develop visceral organs such as stomachs and inter lines , rather than retaining the open digestive cavity characteristic of diploblastic animls.