Sperm cell

The sperm cell is the male gamete, meaning the cell the father contributes toward forming an embryo. It is haploid, which means it carries half the chromosomes of an ordinary cell. It arises from germ cells, the ones set aside to produce gametes, in a process called spermatogenesis.

All of this happens inside the seminiferous tubules, coiled ducts that sit in the testis. There, meiosis, a special kind of cell division, turns diploid cells, which carry the full set of chromosomes, into haploid cells. Then comes spermiogenesis, the final stage in which those round cells are reshaped into mature sperm that can move.

Its shape serves a purpose. The nucleus packs down tight and the acrosome sits at the front; both are needed to make contact with the female gamete. And it moves with a single flagellum. A compact head with a tool up front and a whip behind.