Question

Name the embryonic phase which changes zygote into blastula.

Answer 1

Hint: The word Biology means the science of life. After the death of an individual, its species continues to live through millions of years unless threatened by nature. For the species to maintain survival reproduction becomes vital where humans undergo sexual reproduction as it has gametes (male and female) which fuse to form a zygote or an embryo followed by an order of events.

Complete answer:
Sexual reproduction is elaborate, complex and slow process as compared to asexual reproduction. All organisms have to reach a certain stage of growth and maturity in their life, before they can reproduce sexually which is called the juvenile phase. Sexual reproduction is divided into three stages namely the pre-fertilisation, fertilisation, and the post-fertilisation events.

Gametes are haploid cells. The male gamete is the sperm and female gamete is the egg or ovum. The most vital event of sexual reproduction is the fusion of gametes which is called syngamy and it forms the diploid zygote.

Embryogenesis refers to the process of embryo development from the zygote after fertilisation. The zygote initially undergoes a cleavage and a series of phases where its size increases from a two celled to four celled and finally to eight celled structure. The final eight celled structure again undergoes division forming a mass of cells numbering twelve to fifteen which is the morula.

Blastula is the next stage where the size increases more from twelve to fifteen cells to hundred cells having a cavity filled with yolk in the middle. Blastula becomes a blastocyst and this is the next stage in embryonic development.

Note: The flowering plants undergo fertilisation in which the ovary develops into fruit and ovules mature into seeds. In angiosperms a special process called pollination ensures transfer of pollen grains which carry the pollen grains from another to stigma. Organisms can be bisexual or unisexual which is varied in plants. Plants are defined as monoecious and dioecious.