04 Structure of the sperm
A microscopic cell with:
- Head: contains the nucleus with 23 chromosomes (haploid). At the front there is the acrosome, which secretes the enzyme hyaluronidase that dissolves part of the coat of the ovum and so helps the sperm to penetrate.
- Neck: contains two centrioles, important in the first division of the fertilised ovum (the centriole forms the spindle).
- Middle piece: contains many mitochondria that supply the energy (ATP) for movement of the tail.
- Tail: a long axial filament ending in a terminal piece (caudal piece) that moves like a whip and propels the sperm.
✍️ Worked examples
Worked example 10.
- A man's sperms have normal heads but immotile tails.
- Which structure is probably defective?
- The middle-piece mitochondria (or tail filament) — no energy or no propulsion, so they cannot reach the egg.