A Level Biology Practice Exam

What defines the initial diploid cell formed during sexual reproduction?

1. A gamete

2. An embryo

3. A zygote

4. A mature cell

The correct answer is: A zygote

The initial diploid cell formed during sexual reproduction is known as a zygote. This unique cell is created when two gametes—one from each parent—fuse together during the process of fertilization. Gametes, which are haploid, contain half the number of chromosomes needed for a complete organism. When fertilization occurs, the fusion of the male and female gametes restores the diploid number of chromosomes necessary for traditional cellular functions and development. The zygote then begins to undergo cell division and develops into an embryo as it differentiates and grows into a multicellular organism. By definition, a mature cell does not describe this initial fusion event, as that term typically refers to cells that have completed their development and specialization within an organism. Thus, referring to the early cell following fertilization as a zygote accurately captures its role as the starting point of new life in many organisms.