Answer: The human sperm is a minute, motile, microscopic cell about 60 µm long. It is divided into head, neck, middle piece and tail, covered by the plasma membrane.
- Head: flat, oval; contains a large haploid nucleus (23 chromosomes) with condensed chromatin. At its tip is a cap-like acrosome formed from the Golgi complex, which contains lytic enzymes (hyaluronidase, acrosin, etc.) that help the sperm penetrate the egg membranes.
- Neck: very short; contains the proximal centriole (which helps in the first cleavage of the zygote) and the distal centriole (which gives rise to the axial filament of the tail).
- Middle piece: contains the axial filament surrounded by spirally arranged mitochondria (mitochondrial spiral / nebenkern) that produce ATP for sperm movement. It ends in a ring centriole (annulus).
- Tail: long, slender, the longest part; consists of the axial filament surrounded by a thin cytoplasmic sheath (main piece) and a naked end piece. Its whiplash movements help the sperm swim in the female genital tract.
[Diagram to be drawn: a human sperm with labels: acrosome, nucleus (head), proximal centriole, distal centriole (neck), mitochondrial spiral, axial filament, ring centriole (middle piece), tail with main piece and end piece, plasma membrane.]
