Blastulation:
- Blastulation is the process of formation of blastula from the zygote, which is the first stage of embryonic development.
- It occurs in the early stage of development, after fertilization and before gastrulation.
- Blastula is a hollow ball-like structure composed of a single layer of cells called blastomeres.
- The process of blastulation involves the rapid division of the zygote through repeated mitotic cell divisions called cleavage.
- The zygote undergoes multiple rounds of cell division without any increase in the size of the embryo.
- These cell divisions result in the formation of a solid mass of cells called the morula.
- The morula then undergoes further cell divisions and rearrangements to form the blastula.
- The blastula consists of an outer layer of cells called the blastoderm or trophoblast and an inner cavity called the blastocoel.
- Blastulation is crucial for the formation of the blastocoel, which is necessary for subsequent developmental processes such as gastrulation.

Gastrulation:
- Gastrulation is the process by which the blastula undergoes extensive cell movements and rearrangements to form the three germ layers: ectoderm, mesoderm, and endoderm.
- It occurs after blastulation and is a key event in the development of most multicellular organisms.
- Gastrulation involves the invagination or involution of cells, resulting in the formation of an embryonic structure known as the gastrula.
- The gastrula consists of three distinct germ layers that give rise to different tissues and organs in the organism.
- The outermost layer is called the ectoderm, which gives rise to the nervous system, skin, and other external structures.
- The middle layer is the mesoderm, which gives rise to the musculoskeletal system, circulatory system, and other internal structures.
- The innermost layer is the endoderm, which gives rise to the digestive system, respiratory system, and other internal organs.
- Gastrulation also involves the formation of a primitive streak or blastopore, which serves as the site for cell invagination and movement.
- The process of gastrulation establishes the basic body plan of the developing organism and sets the stage for further differentiation and organ development.

In summary, blastulation is the process of forming the blastula, a hollow ball-like structure, from the zygote through rapid cell divisions. Gastrulation, on the other hand, is the subsequent process where the blastula undergoes extensive cell movements and rearrangements to form the three germ layers, which give rise to different tissues and organs in the organism.

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