AP BIOLOGY

Detailed explanation-1: -During cleavage the relatively enormous zygote directly subdivides into many smaller cells of conventional size through the process of mitosis (ordinary cell proliferation by division). These smaller cells, called blastomeres, are suitable as early building units for the future organism.

Detailed explanation-2: -Zygotes divide through a process known as mitosis, in which each cell doubles (one cell becomes two, two becomes four, and so on). This two-week stage is known as the germinal period of development and covers the time of fertilization (also called conception) to the implantation of the blastocyst in the uterus.

Detailed explanation-3: -After fertilization, the zygote undergoes cleavage to form the blastula. The blastula, which in some species is a hollow ball of cells, undergoes a process called gastrulation, in which the three germ layers form.

Detailed explanation-4: -Fertilization is the process in which haploid gametes fuse to form a diploid cell called a zygote.

Detailed explanation-5: -The zygote undergoes mitosis to form two identical cells that remain attached. This takes place about 36 hours after fertilization. Mitosis then occurs more frequently. Soon a solid ball of cells, a morula, results.