Question

describe the basic function for fertilization, cleavage, gastrula and neurulation.

Answer 1

Fertilization involves fusion of male and female gametes (sperm and egg). This fusion of two cells stimulate the egg to begin development and forms a new individual. Zygote is formed from this fusion, which undergo further division of cells and form the embryo. Fertilization accomplishes several things. Firstly, haploid nucleus of egg and haploid nucleus of sperm merge to form diploid zygote. Secondly, cytoplasmic migration is important for determining body axes. Third, all those molecules which are necessary to begin cleavage and gastrulation are activated.

Cleavage is a series of extremely rapid mitotic divisions just after the fertilization. During cleavage, cytoplasm is divided into numerous cells called blastomeres. By the end of cleavage, blastomeres are arranged in a sphere, known as blastula. Meanwhile, fluid filled cavity is formed in the center of sphere, known as blastocoel. ( In amphibians).

Gastrulation is the next step after the mitotic divisions slow down. Now the cells tend to rearrange themselves with dramatic movements. This series of rearrangements is called gastrulation. The embryo is now called Gastrula.  As a result of gastrulation, three germ layers are formed, endoderm, ectoderm and mesoderm, these further form organs of body.

Neurulation involves transformation of neural plate into neural tube in vertebrate embroys. Embryo at this stage is known as neurula. It involves two different processes: primary neurulation : neural plate creases inwards and edges come in contact and fuse. Secondary neurulation : the tube forms by hollowing out of a solid precursor. Various cavities are formed that merge to form a single tube.