OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What is the ball of cells formed from a zygote known as after the first few divisions?

Blastocyst
Fetus
Embryo
Gamete

The correct answer is: Embryo

The correct answer is "embryo." After a zygote is formed through the fertilization of an egg by a sperm, it begins to undergo a series of cell divisions known as cleavage. During these early stages of development, the single-celled zygote divides multiple times, leading to the formation of a hollow ball of cells known as a blastocyst. However, before reaching the blastocyst stage, the initial mass of dividing cells is referred to as an embryo. The term "embryo" encompasses the developing organism from the moment of fertilization until the end of the eighth week of pregnancy, at which point it is considered a fetus. The term "blastocyst" specifically describes the stage that follows the embryo stage, characterized by a fluid-filled cavity within the ball of cells. "Fetus" refers to a later stage of development after the embryonic phase, specifically after the eighth week of gestation. "Gamete,” on the other hand, refers to the reproductive cells (sperm and egg) and is not related to the cell divisions following fertilization.