IB Biology Exam Prep

Answer: A, zygote-morula-blastula-embryo. This is the development pattern of fertilized eggs in humans.

Key Takeaway: The zygote is formed when the egg fuses with the sperm, creating a single, diploid cell. The zygote then divides by mitosis until a solid ball of cells known as the morula develops.

Further development of this ball into a more organized state results in formation of the blastula. As development continues, cells of the inner core of the blastula go on to form the embryo. By only remembering that the zygote is the first stage and the embryo is the last stage, a student can eliminate three of the choices immediately.