Which statement about gastrulation is true? a. In frogs,...

Which statement about gastrulation is true? a. In frogs, gastrulation begins in the vegetal hemisphere. $b,$ In sea urchins, gastrulation produces the notochord. $c .$ In birds, cells from the surface of the blastodisc move down through the primitive groove to form the hypoblast. $d$. In mammals, gastrulation occurs in the hypoblast. $e .$ In sea urchins, gastrulation produces only two germ layers.

Which statement about gastrulation is true?
a. In frogs, gastrulation begins in the vegetal hemisphere.
$b,$ In sea urchins, gastrulation produces the notochord.
$c .$ In birds, cells from the surface of the blastodisc move down through the primitive groove to form the hypoblast.
$d$. In mammals, gastrulation occurs in the hypoblast.
$e .$ In sea urchins, gastrulation produces only two germ layers.

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Key Concepts

Gastrulation

Gastrulation is a fundamental phase in embryonic development during which the single-layered blastula is reorganized into a multilayered structure called the gastrula. This process establishes the three primary germ layers—ectoderm, mesoderm, and endoderm—that ultimately give rise to all tissues and organs of the organism.

Germ Layer Formation

Germ layer formation is the process by which cells in the early embryo differentiate into three primary layers: the ectoderm, mesoderm, and endoderm. Each of these layers is tasked with forming specific tissues and organ systems, making this specification a crucial event in defining the body plan of an animal.

Blastopore

The blastopore is an opening that forms during gastrulation in many organisms such as amphibians. It marks the site where cells begin to move inward during the process of invagination or involution, initiating the formation of the internal germ layers and establishing the body axes.

Primitive Streak/Groove

The primitive streak or groove is a structure that forms on the surface of the early embryo in birds and mammals. It serves as the primary organizer for cell movements during gastrulation, guiding the migration of cells from the epiblast to form the various germ layers and contributing to the overall establishment of the embryo’s bilateral symmetry.

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