Question

Name the embryonic phase which changes zygote into blastula.

Answer 1

Fertilization involves fusion of the male gamete i.e. sperm with female gamete i.e. the ovum to form a zygote. This zygote is the single-celled stage from which multi-cellular organisms such as the human beings are formed. This single-celled zygote stage first undergoes cleavage to form a 2-celled then a 4-celled and finally an 8-celled structure. This 8-celled stage undergoes further division to form a solid mass of 12-15 cells which is called the morula. This morula then divides further to form a mass of close to 100 cells. This mass of 100 cells have a yolk-filled cavity in the middle and is called the Blastula. In mammals, the blastula develops into the blastocyst which is the next stage in the embryo development.