Praxis II: Biology Content Knowledge Exam Prep

Answer: A, When a sperm cell fuses with an egg cell, this results in the formation of a zygote. The diploid zygote is the first stage of the development of a human.

Key Takeaway: The fertilization of an egg by the sperm is the first step in the development of a human. The zygote divides by mitosis until it forms a solid ball of cells called the morula. The morula is then implanted in the uterine wall and further divides to form the blastula. The blastula is the stage where cells begin to differentiate, and this growth gives rise to the gastrula. The gastrula first exists in two layers, but a third layer forms later, and it is these three layers of cells that gives rise to all the tissues and structures of the body. Once the organs are constructed, the embryo is now called a fetus.