Define Primary Sex Characteristics.

Primary sex characteristics refer to the physical structures and organs that are directly involved in reproduction and sexual differentiation between males and females. These characteristics develop during fetal development and puberty under the influence of sex hormones (such as testosterone and estrogen).

In males, primary sex characteristics include:

• Penis: The male reproductive organ responsible for transferring sperm during sexual intercourse.
• Testes: The male gonads that produce sperm and testosterone.

In females, primary sex characteristics include:

• Vagina: The female reproductive organ that receives the penis during sexual intercourse and serves as a birth canal.
• Ovaries: The female gonads that produce eggs (ova) and female sex hormones like estrogen and progesterone.

These primary sex characteristics distinguish biological males from females and are essential for reproduction. They are distinct from secondary sex characteristics, which develop during puberty and are related to physical appearance, voice changes, and body hair distribution.