Question

What are the first two tissue layers that form in an animal, what do they become, and why are they important? Would you expect these tissue layers to be different in terrestrial vs. aquatic organisms.

Answer 1

Animals develop either two embryonic germs layers. The animals that display radial symmetry develop two germ layers, an inner layer (endoderm) and an outer layer (ectoderm). These animals are called diploblasts.

The germ layers represent some of the first lineage-specific (multipotent) stem cells (e.g., cells destined to contribute to specific types of tissue, such as muscle or blood) in embryonic development. Hence, each germ layer eventually gives rise to certain tissue types in the body.

Importance :-

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 all organs and tissues.Together, germ layers will give rise to every organ in the body, from skin and hair to the digestive tract.

Tissues in Terrestrial animals :-

In animals having discoidal cleavage, the three germinal layers at the end of gastrulation are stacked flat; ectoderm on top, mesoderm in the middle, and endoderm at the bottom. The embryo is produced from the flattened layers by a process of folding to form a system of concentric tubes.

Tissues in aquatic animals :-

These animals are called diploblasts. Animals with bilateral symmetry develop three germ layers: an inner layer (endoderm), an outer layer (ectoderm), and a middle layer (mesoderm). Animals with three germ layers are called triploblasts.